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Panaitescu, D.M.; Usurelu, C.; , .; Frone, A.N. Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals. Encyclopedia. Available online: https://encyclopedia.pub/entry/23130 (accessed on 04 September 2024).
Panaitescu DM, Usurelu C,  , Frone AN. Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals. Encyclopedia. Available at: https://encyclopedia.pub/entry/23130. Accessed September 04, 2024.
Panaitescu, Denis Mihaela, Catalina Usurelu,  , Adriana Nicoleta Frone. "Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals" Encyclopedia, https://encyclopedia.pub/entry/23130 (accessed September 04, 2024).
Panaitescu, D.M., Usurelu, C., , ., & Frone, A.N. (2022, May 19). Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals. In Encyclopedia. https://encyclopedia.pub/entry/23130
Panaitescu, Denis Mihaela, et al. "Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals." Encyclopedia. Web. 19 May, 2022.
Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals
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This entry is adapted from the peer-reviewed paper 10.3390/polym14101974

Poly(3-hydroxybutyrate) (PHB) is one of the most promising substitutes for the petroleum-based polymers used in the packaging and biomedical fields due to its biodegradability, biocompatibility, good stiffness, and strength, along with its good gas-barrier properties. One route to overcome some of the PHB’s weaknesses, such as its slow crystallization, brittleness, modest thermal stability, and low melt strength is the addition of cellulose nanocrystals (CNCs) and the production of PHB/CNCs nanocomposites. Choosing the adequate processing technology for the fabrication of the PHB/CNCs nanocomposites and a suitable surface treatment for the CNCs are key factors in obtaining a good interfacial adhesion, superior thermal stability, and mechanical performances for the resulting nanocomposites. 

nanocomposites polyhydroxyalkanoates cellulose nanocrystals

1. Poly(3-hydroxybutyrate)

Poly(3-hydroxybutyrate) (PHB) is the most well-known and widely used member of polyhydroxyalkanoates (PHAs) [1], a family of biodegradable polyesters derived from the microbial fermentation of different carbon sources [2]. Although chemical synthesis is also possible [3], the main method of producing PHB is its extraction from various bacterial strains which are capable of synthesizing and accumulating PHB intracellularly, as carbon and energy reserve, under nutrient limiting conditions [4]. Due to its biodegradability in both soil and marine environments [5], non-toxicity, biocompatibility, and a melting temperature, elastic modulus and tensile strength similar to that of isotactic polypropylene [6], PHB has drawn increasing attention as an environmentally friendly substitute for petroleum-based thermoplastics, such as polypropylene (PP) and polyethylene (PE) [7]. The world’s rising concern on plastic pollution and oil resources depletion supported the study of PHB—based materials for potential applications in packaging (films, bags, bottles, containers etc.) [8], biomedicine (surgical sutures, drug delivery systems, surgical meshes, wound dressings, scaffolds for tissue engineering etc.) [9] and agriculture (carriers for the slow release of pesticides, herbicides, fertilizers etc.) [10]. However, the high degree of crystallinity of PHB [11] that imparts brittleness [12], the thermal degradation at temperatures just above its melting temperature [13] that narrows its processing window [7], the low elongation at break [14] and the high production costs [12], are serious disadvantages which have restrained the use of PHB on a large scale [15].
In recent years, efforts have been made to eliminate these disadvantages. For example, in order to reduce the production costs of PHB, the replacement of the noble carbon sources such as glucose, mannose, and lactose [16] with low-cost agro-industrial byproducts and residues has been proposed [17]. Waste glycerol from biodiesel fuel production [18], corn waste [19], wheat straw [20], rice straw [21], dairy waste [22], sugarcane vinasse, and molasses [23] are just a few of the industrial and agricultural by-products and residues that were successfully employed as carbon sources in the obtaining of PHB by microbial fermentation [24]. Regarding the improvement of the mechanical properties and thermal stability of PHB, several methods have been developed. One method consists in the incorporation of secondary flexible monomers such as 3-hydroxyvalerate, 4-hydroxybutyrate, or 3-hydroxyhexanoate [25] in the main chain of PHB that led to the formation of PHBV [26], poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (P4HB) [27], or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHH) [26] copolymers. Despite the fact that these PHB copolymers have shown higher flexibility, lower melting temperatures and wider processing windows as compared to the pristine PHB [28], they still have poor mechanical properties or are difficult to be obtained through efficient synthesis processes, which has limited their utilization for commercial use [29]. A second strategy involves the use of petroleum-based (dioctyl adipate, dioctyl phthalate, dibutyl phthalate, polyethylene glycol, polyadipates etc.) or bio-based (glycerol, glycerol triacetate, triethyl citrate, soybean oil, epoxidized soybean oil etc.) [30] plasticizers, which are known to increase the flexibility of PHB and to decrease its glass transition temperature (Tg). However, plasticizers may degrade at temperatures lower than PHB, accelerating its thermal degradation during melt processing, or migrate at the surface of the material, altering its mechanical properties [31]. A third method implies the melt blending of PHB with polymers such as medium chain length-PHAs [32], poly(caprolactone) (PCL), polyethylene glycol (PEG), poly(butylene adipate-co-terephthalate) (PBAT), and poly(butylene succinate) (PBS) etc. [32][33][34]. In this case, it has been shown that the obtained blends have improved flexibility, toughness, and processability as compared to the pure PHB. However, in many situations the improvements were not at the anticipated level due to the poor miscibility between PHB and the second polymer in the melt state [35]. Another method involves the addition to PHB of various nanofillers such as titanium dioxide (TiO2) [36], zinc oxide (ZnO) [37], carbon nanotubes (CNTs) [38], clays [39], and nanocellulose [40][41]. Using these nanofillers makes possible the obtaining of PHB-based nanocomposites with superior thermal stability and increased mechanical and barrier properties as compared to the neat PHB [36][37][38][39]. Among them, special attention has been paid to nanocellulose fillers due to their renewability, biodegradability, and superior mechanical properties.

2. Cellulose Nanocrystals

Cellulose is the nature’s most abundant biopolymer and can be extracted from various sources such as plants, marine life, fungi, and bacteria [42]. Regardless of its source, the prime structural unit of cellulose is comprised of linear chains of D-glucose linked by repeating β-1,4-glycosidic bonds, followed by a 180° rotation for the next linkage [42][43]. Owing to its large network of intermolecular and intramolecular hydrogen bonds, cellulose is insoluble in water and most organic solvents. The degree of polymerization and molecular weight of cellulose are governed by both the cellulosic source and the methods employed to produce it [44]. Cellulose with nano-scale structural dimensions, referred to as nanocellulose, possesses high surface area, unique morphology, specific high strength and modulus, renewability, customizable surface chemistry, and good biocompatibility, offering myriad of opportunities for medical and engineering applications. As filler in polymers, nanocellulose has the advantage of being a stable material that cannot be melted during melt processing due to the high level of hydrogen bonding. Thus, nanocellulose can be used as a reinforcing agent for biopolymers, especially in the field of industrial packaging, where the melt processing techniques specific to thermoplastic polymers are intensively used [44].
Depending on the preparation methods and sources, nanocellulose can be classified into three categories, namely cellulose nanocrystals (CNCs), cellulose nanofibers (CNFs), and bacterial nanocellulose (BC). CNCs are one of the most important nanocelluloses that are produced at an industrial level using chemical treatments. Besides the wood and lignocellulosic fibers, a more convenient alternative from both an environmental and an economic point of view is represented by the agriculture along with food and beverage-processing waste and byproducts. Thus, CNCs are predominantly extracted from corn cobs [45], tea stalk [46], soy hulls [47], apple [48] and grape pomace [49], pineapple leaves [50], soybean [51], plum shells [52], barley [53] and garlic [54] straws, tomato peel waste [55], sugarcane bagasse [56], orange peel waste [57], or chili leftovers [58]. However, the exploitation of municipal waste and papermaking sludge may represent other alternative sources [43][59].
Different strong (sulfuric, hydrochloric and hydrobromic acids) and weak (phosphoric, citric and formic acids) acids were used for breaking the glycoside bonds in cellulose [60]. Acid hydrolysis involves the hydrolytic cleavage of the amorphous regions from the cellulose fibers, when the crystalline region domains are left behind. Reaction temperature and duration as well as the acid type and its concentration are the main parameters that determine the size and morphology of the isolated CNCs [61]. Thus, CNCs possess whisker or a short-rod-like morphology with uniform sizes ranging from 100 to 200 nm in length and 10 to 30 nm in diameter [62][63]. The use of weak acids leads to cellulose fibers with low crystallinity and fibrous morphology as a result of the low dissociation constant of these acids [61]. Despite being a simple and fast isolation method, sulfuric acid hydrolysis has the advantage of yielding CNCs with higher crystallinity degree (over 90%) and also leads to the sulfate esterification of the CNCs surface, which enhances CNCs’ phase stability in aqueous medium [64]. However, sulfate esterification decreases their thermal stability in the case of thermal treatments. Moreover, CNCs’ almost perfect crystalline structure ensures high mechanical properties such as tensile modulus and tensile strength, which are crucial for further applications [65]. It is worth mentioning that when incorporated in the polymer matrices, CNCs develop a network-like formation, upgrading the polymer’s gas barrier and migration properties to a greater extent than the nanoclays or carbon-based materials [66]. However, the strong hydrophilic property of CNCs raises compatibility and dispersibility issues when combined with other polymers, especially with highly hydrophobic ones. Thus, extensive research studies have been conducted for the surface treatment of CNCs in order to overcome these problems [65].
CNFs, also known as nanofibrillar cellulose and cellulose nanofibers, possess hierarchical structures made up of interconnected fibrils with diameters ranging from 1 to 100 nm and an aspect ratio higher than 15 [67][68]. Top-down mechanical disintegration methods such as grinding, cryocrushing, high-intensity ultrasonication, and high-pressure homogenization are usually employed for the CNFs’ isolation. Through these techniques, dilute suspensions of cellulose fibers are subjected to high shear and impact forces, thus leading to mechanical cleavage along the longitudinal direction of the cellulosic source [63][67][68][69]. Specifically, the defibrillation methods yield nanostructures with both crystalline and amorphous regions. The high flexibility of CNFs is due precisely to the presence of the amorphous component. However, due to their large aspect ratio, the mechanical derived nanocelluloses are more susceptible to fiber agglomeration, which makes their further processing more challenging.
Alternatively, BC, named bacterial nanocellulose, microbial cellulose, or bio-cellulose, is produced through a bottom-up approach using different aerobic non-pathogenic bacteria [68][69][70]. Besides being the purest form of nanocellulose, BC shows an ultrafine network structure containing fibers with micrometers in length and 20–100 nm in diameter, high water holding capacity and flexibility, and high crystallinity. Its outstanding physical, structural, and mechanical features make BC an ideal candidate for biomedical applications.
Nanocelluloses, regardless of their source or preparation method, have been intensively studied as reinforcements in biopolymers for improving their mechanical and barrier properties [40][41][71][72]. The biocomposites from aliphatic polyesters and bacterial cellulose, as well as the nanocomposite materials from microfibrillated cellulose and hydrophilic or hydrophobic polymers, have been already reviewed [73][74]. However, much recent literatures on nanocellulose based materials are focused on biopolymers reinforced with CNCs. CNCs may be easily obtained both in labs and industrial facilities by employing less energy intensive processes as compared to CNFs. Due to the bio-origin of both PHB and CNCs and their subsequent biodegradation to carbon dioxide and water, the PHB/CNCs nanocomposites are of particular interest in the context of the world’s transition towards a circular economy.

3. PHB Nanocomposites with Cellulose Nanocrystals

3.1. Preparation Routes

Solvent casting, melt processing, and electrospinning are the most used methods for obtaining PHB or PHBV nanocomposites with cellulose nanocrystals [75][76][77]. From these, solution casting is used more frequently due to some advantages such as its simplicity, easy application in lab conditions, and the obtaining of a good dispersion of the cellulose nanocrystals in the polymer matrix. However, this method has the drawback that it uses toxic solvents thatare difficult to be entirely removed from the samples. Moreover, the largely different character of cellulose and PHB, strongly hydrophilic vs. hydrophobic, and, therefore, the different solvents needed to dissolve the PHB and disperse the CNCs, make difficult the mixing of their solutions. Melt processing by using batch mixers, kneaders, or twin-screw extruders followed by injection or compression molding is advantageous because it can be easily transposed in industry, being an environmentally friendly method, which does not use dangerous solvents. However, the specialized equipment required for performing this process, the energy consumption needed for melting the PHB and for the mixing process, and the tendency of the cellulose nanocrystals to aggregate in the polymer melt are several disadvantages that must be overcome. In addition, PHB is sensitive to thermal degradation during melt processing [14][78]. Electrospinning has advantages related to easy scale-up, inexpensiveness and ability to incorporate various additives and polymers in the process, however it suffers from the same drawbacks as the solvent casting method, related to toxicity and difficult removal of the solvent. Additive manufacturing or reactive blending [79], processing under supercritical conditions or foaming [80] were also tried as new routes to obtain PHB nanocomposites with cellulose nanofillers.

3.1.1. Solution Casting

CNCs extracted from different sources (bamboo pulp, microcrystalline cellulose (MCC), or bleached pulp board) by sulfuric acid hydrolysis were used to obtain PHB/CNCs nanocomposites by solution casting using chloroform or dimethylformamide (DMF) as a solvent. Several methods were used to disperse the CNCs into the PHB solution: (i) a CNCs suspension in water was dispersed in acetone and then in chloroform through a sequential solvent exchange process consisting of a succession of dispersions and centrifugations, and further the CNCs dispersion in chloroform was mixed with a chloroform solution of PHB [75][81][82]; (ii) the CNCs were transferred from water to DMF using a solvent exchange method and then mixed with the PHB solution in DMF [62]; (iii) the water suspension of CNCs was lyophilized, and then the CNCs were redispersed in DMF and finally mixed with the DMF solution of PHB [72][83][84][85][86][87]. The concentration of CNCs in PHB was maintained at low values of up to 6 wt% in all the reported works. At a CNCs concentration below 2 wt%, a homogeneous dispersion of the CNCs in the PHB matrix was obtained, while at higher contents, CNCs agglomerations were observed with the naked eye as small white dots distributed in the transparent PHB matrix [81]. Due to their ability to scatter light, the CNCs agglomerates led to a decrease in the transparency of the PHB/CNCs nanocomposites. FESEM images showed that the CNCs were homogeneously dispersed into the PHB matrix at a CNCs content of 1 wt% [81]. Similar results were reported by Zhang et al. [75] which prepared PHB/CNCs and PHB/CNFs nanocomposites with a nanocellulose content of 1, 3, and 5 wt%, using a solution casting method. The SEM images showed that the best dispersion of CNCs in the PHB matrix was obtained at a CNCs loading of 1 wt%, while at CNCs contents of 3 and 5 wt%, a high tendency of CNCs to form agglomerates was noticed. This was due to the strong hydrogen bonds formed between the CNCs nanoparticles at these higher concentrations [75]. The transparency tests revealed that the transmittance of the PHB/CNCs and PHB/CNFs nanocomposite films decreased with the increase of CNCs and CNFs concentration. This was attributed to the poor compatibility between the hydrophilic nanocellulose and the hydrophobic PHB matrix and to the formation of nanocellulose agglomerates, which prevent light transmission [75]. When PHB/CNCs nanocomposites with 2, 4 and 6 wt% CNCs were compared to a PHB/2 wt% BC nanocomposite, all of them being obtained by solution casting, the transparency tests showed that the transmittance of the nanocomposites was higher as compared to that of pure PHB [72]. The best transparency was observed for the PHB/CNCs films due to the good CNCs dispersion and favorable interactions between the CNCs and the PHB matrix [84].
Several methods were applied to improve the properties of PHB/CNCs nanocomposites obtained by solution casting, such as the addition of plasticizers or the use of PHBV copolymer instead of PHB. Different plasticizers were added to the PHB/CNCs nanocomposities during the solution mixing and casting process to improve their flexibility and processability [85][87]. For example, PHB/CNCs nanocomposites with a CNCs loading of 2 and 4 wt%, respectively, and 20 wt% glyceryl tributyrate (TB) or poly [di (ethylene glycol) adipate] (A) as plasticizers were prepared via solvent casting using DMF as a solvent. TB addition led to PHB/CNCs nanocomposites with a lower thermal stability than that of pure PHB due to its easy evaporation and increased mobility of the polymer chains, which facilitated the diffusion of the decomposition products. On the contrary, the addition of plasticizer A led to PHB/CNCs nanocomposites with higher thermal stability than neat PHB due to the high molecular weight of A plasticizer which prevents its migration from the nanocomposites. CNCs addition was shown to have a beneficial effect on the stiffness and barrier properties of the plasticized nanocomposites, especially in the case of TB containing nanocomposites. This was explained by the good dispersion of the CNCs in the TB plasticized-PHB matrix due to the good compatibility between TB and the PHB matrix and the favorable hydrogen-bonding interactions established between TB and CNCs [85]. Therefore, the addition of TB plasticizer enhanced the PHB—CNCs interactions and improved the dispersion of the CNCs [87]. The decrease in the contact angle (CA) value for the PHB/CNCs nanocomposites as compared to pure PHB, regardless of whether CNCs or BC was used as reinforcing agent and whether A or TB was used as plasticizer, indicated an increased hydrophilicity. This may be assigned to various causes: (i) the plasticizing effect of TB or A, which led to an increased mobility of the PHB chains facilitating the diffusion of water into the material, (ii) the existence of numerous hydrophilic groups on the CNCs surface, which might have increased the hydrophilicity of the material or (iii) the poor dispersion of BC in the PHB matrix, which left a higher mobility to the PHB chains, favoring the diffusion of water molecules inside the material. However, CA values did not decrease below 65°, except for the PHB/4 wt% CNCs nanocomposite (A plasticizer) [87]. The PHB/CNCs nanocomposite films, containing 20 wt% TB, were applied as coatings on a cellulose paperboard by compression molding [86]. The CNCs from the nanocomposite films increased the interaction between layers as a result of the hydrogen bonding interactions between the hydroxyl groups from their surface and the OH groups of the paperboard, leading to enhanced mechanical properties. In addition, the PHB/CNCs layer improved the barrier properties of the paperboard, which became more suitable for packaging applications [86].
PHB/CNCs nanocomposites containing 15 wt% PEG and a low amount of CNCs (up to 0.75 wt%) were prepared by a solvent casting method [88]. PEG was used as a plasticizer and compatibilizer based on its miscibility with PHB and its affinity to cellulose due to the formation of hydrogen bonds between the carbonyl (-C=O) groups of PEG and the hydroxyl (-OH) groups of CNCs. The CNCs were first dispersed in PEG, the CNCs surface being covered by a PEG layer. Indeed, the TEM images revealed a homogeneous dispersion of the CNCs in the PHB matrix at a CNCs content of 0.15 wt%. This confirmed the ability of PEG to act as a coupling agent between PHB and CNCs. Based on the ATR-FTIR spectra and the electron microscopy images of the PHB/PEG/CNCs nanocomposites, it was supposed that (i) for a CNCs s content up to 0.45 wt% nearly the entire surface of the CNCs was covered by PEG, so that all or almost all the interactions between the PHB and the CNCs occurred preferentially via their PEG coating; (ii) for a higher CNCs content, when the PEG/CNCs ratio was low, the amount of PEG was no longer enough to cover the entire surface of CNCs, so that the interactions between PEG and PHB decreased, becoming more likely that the CNCs interacted directly with the PHB matrix. This model was supported by the variation of the mechanical properties of the nanocomposites, up to a concentration of 0.45 wt% the PEG-coated CNCs showing no reinforcing effect [88].
The use of PHBV instead of PHB in the nanocomposites with CNCs was also tried as a method to improve the processability and flexibility of the nanocomposites [83][89]. Two methods were used to incorporate the CNCs in PHB. In one method [83], the gel-like CNCs, resulting from the sulfuric acid hydrolysis of microcrystalline cellulose (MCC), were freeze-dried. Then, the resulting powder was added to the PHBV solution in DMF, ultrasonicated and casted. Transparent films containing 1–5 wt% CNCs were thus formed [89]. In the second method [83], water suspensions with different concentrations of CNCs were added dropwise in DMF under stirring and, after the evaporation of water, PHBV was dissolved in the CNCs suspensions. PHBV/CNCs films with 0.5–4.6 wt% CNCs were obtained by solution casting, similar to the first method. The PHBV/CNCs films obtained by the two methods showed different thermal and mechanical properties [83][89]. Thus, a continuous decrease of the cold crystallization temperature (Tcc) with the increase of the CNCs concentration was observed in the nanocomposites obtained by the first method and a decrease in Tcc only at loadings lower than 2.3 wt% in the second case. A similar trend was noticed for the variation of the mechanical properties, which indicated a more homogeneous dispersion of the CNCs in the nanocomposites obtained by the first method and a worse dispersion of CNCs at CNCs loadings exceeding 2.3 wt% when the solvent exchange-solution casting method was employed. The CNCs agglomerations were clearly observed in the TEM image of the PHBV/4.6 wt% CNCs film [83].

3.1.2. Melt Processing

Melt processing may be considered as the most important method to obtain PHB/CNCs nanocomposites due to the eco-friendliness and good fitting to the industrial processing techniques. However, the incorporation of CNCs in the PHB melt may be a difficult task due to the high tendency of hydrophilic CNCs to agglomerate in a hydrophobic environment.
Chen et al. [90] used freeze-dried CNCs obtained by the sulfuric acid hydrolysis of MCC to prepare PHB/CNCs nanocomposites. A melt mixing method using a Haake Polylab Rheometer heated to 180 °C was employed to incorporate 2 wt% CNCs into the PHB and the resulted nanocomposite was subjected to crystallization studies to determine the CNCs effect on the PHB crystallization. Compared to MCC, CNCs had a higher influence on the spherulite morphology of PHB. CNCs acted as a heterogeneous nucleating agent causing an increase in the PHB crystallization rate simultaneously with a decrease in the energy barrier of PHB nucleation and in the folding surface free energy [90]. In addition, CNCs incorporation influenced the banded structure of the PHB spherulites, leading to a decrease in the average band space of the ring-banded spherulites. This was assigned to the increase in the crystallization rate of PHB in the presence of CNCs, which led to unbalanced stresses favoring the lamellae twist and the formation of ring-banded spherulites with reduced band space [90].
Jun et al. [76] used a PHBV matrix to prepare nanocomposites with two types of nanocelluloses (CNCs and CNFs) in different concentrations from 1 to 7 wt%. CNCs were obtained via the sulfuric acid hydrolysis of rice straws and CNFs resulted from the pressure-grinding of the cellulose extracted from the same source. For the preparation of nanocomposites, the PHBV powder was added to the nanocellulose suspensions under stirring and the mixtures were vacuum-dried for 24 h. A Haake co-rotating twin-screw extruder was used for melt compounding the mixtures. Both CNCs and CNFs showed a nucleation effect, accelerating PHBV crystallization and improving the Young’s modulus of nanocomposites, the optimum mechanical properties being obtained at 1 wt% CNCs [76].

3.1.3. Other Methods

Electrospinning was used to obtain PHB/CNCs nanocomposite fibers with a content of CNCs of 5, 8, 12, 17, and 22 wt% [77]. CNCs were obtained by the sulfuric acid hydrolysis of alkali-treated and bleached corn husk [91]. A solvent exchange method was used to disperse the CNCs in achloroform/DMF mixture (90/10 volume ratio), which was employed as a solvent in the electrospinning process [77]. As revealed by SEM, the obtained PHB/CNCs nanocomposite fibers presented a uniform surface, without beads, regardless of the concentration of CNCs in the PHB matrix. A decrease of the PHB/CNCs nanocomposite fibers’ diameter was observed with the increase of CNCs concentration in nanocomposites. This was attributed to the increase in the conductivity of the electrospinning solution with increasing CNCs loading as a result of the negatively charged sulfate ester groups formed on the CNCs surface during sulfuric acid hydrolysis [77].
PHB/CNCs nanocomposite foams with 2, 3 and 5 wt% CNCs, obtained via the sulfuric acid hydrolysis of pulp fibers, were prepared using a nonsolvent-induced phase separation (NIPS) method [92]. Chloroform was used as solvent while tetrahydrofuran (THF) or 1,4-dioxane (Diox) was used as nonsolvents. In the NIPS process, the addition of a nonsolvent reduced the polymer−solvent affinity leading to a phase-separated polymer solution with one phase rich in polymer, representing the backbone of the gel, which was penetrated by the polymer-poor phase (in the nonsolvent) [92]. When THF was used as nonsolvent, CNCs accelerated both the PHB crystallization and the nanocomposites gelation, showing a nucleating effect. In contrast, when Diox was used as nonsolvent, CNCs incorporation led to a decrease in both PHB crystallization and nanocomposites gelation rate. This was due to the better dispersion of the CNCs in Diox than in THF, preventing the movement of the PHB chains and delaying the crystals’ growth. However, no significant differences between the degrees of crystallinity of the PHB/CNCs nanocomposites obtained using THF or Diox as nonsolvents were observed [92].
PHB/CNCs (4 wt%) nanocomposites obtained by solution casting using DMF as solvent were compression molded and further applied as a coating to cellulose paperboards, resulting in bilayer structures [93]. The PHB/paperboard ratio was varied between 5 and 20 wt%. The addition of CNCs improved the adhesion between the PHB layer and the cellulosic paperboard. The PHB/CNCs coatings decreased the water sensibility of the cellulose layer, leading to paperboard/PHB-CNCs bilayer composites suitable for packaging [93].

3.2. Methods Used to Improve the Compatibility in PHB/CNCs Nanocomposites

Different methods were applied to improve the compatibility between the strongly hydrophilic CNCs and the hydrophobic PHB matrix [94][95][96][97]. Dispersion agents and compatibilizers are one of the simplest and sometimes efficient additives for improving the compatibility in polymer nanocomposites with CNCs [98]. PEG is a hydrophilic polymer that is miscible with PHBV and, therefore, it was used as a compatibilizer in the PHBV/CNCs nanocomposites [94]. PHBV/CNCs nanocomposites with CNCs contents of 2 and 5 wt% were prepared using solution casting or extrusion blending [94]. In the first method, CNCs were coated with PEG by dispersing the mixture of CNCs and PEG powders in DMF, and then the PHBV solution in DMF along with the CNCs/PEG suspension in DMF were mixed and casted. In the second method, the freeze-dried CNCs/PEG powder was pre-mixed with PHBV and melt compounded using a co-rotating twin screw extruder followed by injection molding [94]. A very good dispersion of the CNCs in the PHBV matrix was obtained when the solvent casting method was used, also supported by the enhancement of the mechanical properties. However, despite the presence of the PEG compatibilizer, the CNCs could not be well dispersed in the PHBV during melt compounding, with effect on the mechanical properties, which decreased as compared to those of pure PHBV. A possible explanation for this behavior is that the high shear stress generated by the twin-screw removed the PEG coat from the CNCs surface and blended it with the PHBV matrix with which is compatible [94].
Another method proposed to improve the dispersion of the CNCs in PHBV and the compatibility between the two components is the chemical modification of CNCs by grafting PHBV onto their surface [96]. OH-terminated PHBV oligomers, prepared through transesterification using ethylene glycol in diglyme and dibutyltin dilaurate as a catalyst, were grafted on the surface of CNCs. The grafting reaction took place in anhydrous DMF using toluene diisocyanate (TDI) as a coupling agent. The ungrafted PHBV was removed by refluxing with chloroform [96]. PHBV-grafted CNCs (PHCNs) were used to obtain PHBV/PHCNs nanocomposites by solution casting, the content of modified CNCs ranging from 5 to 30 wt%. Most of the PHBV/PHCNs nanocomposite films showed a transparency similar to that of pure PHBV films. A decrease in the UV-vis transmittance with an increase in the PHCNs content was noticed; good results were obtained at PHCNs loadings up to 20 wt%, while a strong reduction in the transparency of the PHBV/PHCNs nanocomposites with 25 or 30 wt% PHCNs was observed. This was due to the formation of PHCNs agglomerates in the PHBV matrix at a higher content of modified CNCs [76]. The addition of PHCNs into PHBV led to a great increase in the mechanical properties for PHCNs contents of up to 20 wt%. This was due to the good adhesion between the components and the effective stress transfer at the PHBV-PHCNs interface [96].
CNCs grafted with polylactide (CNC-g-PLA) were prepared and used in PHB as a more compatible reinforcing agent [99]. CNCs resulted from the sulfuric acid hydrolysis of filter paper were grafted with polylactide by surface-initiated ring opening polymerization of L-lactide. The synthesis of CNC-g-PLA was carried out in 1-allyl-3-methylimidazolium chloride ionic liquid in the presence of catalytic amount of (dimethylamino)pyridine. Prior to the ring-opening polymerization of L-lactide, the CNCs were homogeneously acetylated. PHB nanocomposites with 2 wt% CNCs or CNC-g-PLA were obtained using a melt compounding method [99]. The calorimetric results showed a large influence of the CNCs treatment on the crystallization behavior of PHB. Untreated CNCs acted as a heterogeneous nucleating agent enhancing PHB crystallization. A different role was observed in the case of CNC-g-PLA which retarded the nucleation of PHB crystals and acted as an antinucleating agent during PHB crystallization [99]. Therefore, the PHB/CNCs nanocomposite exhibited a higher crystallization rate than neat PHB while the PHB/CNC-g-PLA nanocomposite presented a lower crystallization rate, showing that the crystallization behavior of PHB could be controlled by the CNCs’ treatment [99].
A one pot acid hydrolysis/Fischer esterification process was used to obtain CNCs surface modified with butyric acid, lactic acid, and their mixture in the presence of 37% HCl [95]. To ensure a good dispersion of modified CNCs in PHBV, the CNCs_butyrate, CNCs_lactate and CNCs_butyrate_lactate nanofillers were subjected to a solvent exchange sequence, from water, to ethanol, acetone, and finally, to chloroform. The suspensions of modified CNCs in chloroform were then mixed with the solution of PHBV in chloroform/tetrachloroethane (50/50) and casted [95]. Due to the similarity between the chemical structures of the lactate and butyrate ester moieties grafted on the CNCs surface and that of the PHBV matrix, the adhesion between the polymer matrix and the reinforcing agents was considerably improved and a homogeneous dispersion of the modified CNCs in the PHBV nanocomposites was observed. Consequently, the PHBV/CNCs_butyrate, PHBV/CNCs_lactate and PHBV/CNCs_butyrate_lactate nanocomposites with 2 wt% CNCs showed a considerably improved transparency as compared to the nanocomposites containing unmodified CNCs [95]. However, the dynamical mechanical analysis results confirmed an improved interface only in the PHBV/CNCs_butyrate nanocomposites due to the similarity between the butyrate moieties attached on the CNCs surface and the PHBV matrix, which led to a better dispersion of the CNCs in the polymer matrix.
To improve the compatibility between the CNCs and the hydrophobic matrix, the CNCs were modified with (i) methyltrimethoxysilane (MTMS) resulting CNCs with a hydrophobic surface (MCNCs), (ii) tetraethyl orthosilicate (TEOS) resulting CNCs with spherical SiO2 nanoparticles on their surface (TCNCs) and (iii) TEOS then MTMS, resulting TCNCs with CH3 ends (TMCNCs). The three types of modified CNCs were melt-compounded with PHB/P4HB by extrusion followed by compression molding resulting nanocomposite plates. MCNCs and TCNCs showed a low compatibility with PHB/P4HB and many aggregated nanocrystals were observed in the nanocomposites with 10 wt% modified celluloses. On the contrary, freeze-dried TMCNCs showed a homogenous dispersion in the PHB/P4HB matrix and no nanocrystals agglomeration [97].

3.3. Nanocomposites from PHB Blends and CNCs

The addition of a third polymer in PHB/CNCs nanocomposites was also used as a method to improve the compatibility and the properties of PHB/CNCs nanocomposites [100][101][102][103]. Based on the compatibility of poly(vinylacetate) (PVAc) and PEG with PHB or PHBV and their hydrophilic character, similar to that of CNCs, the two polymers were used as a third component in PHB/CNCs nanocomposites [100]. PHB/PVAc/CNCs, PHB/PEG/CNCs, PHBV/PVAc/CNCs, and PHBV/PEG/CNCs ternary nanocomposites with 2.4 or 4.8 wt% CNCs were prepared by melt mixing PHB or PHBV with PVAc/CNCs and PEG/CNCs masterbatches in a Haake double-screw mini-extruder. The masterbatches were prepared by dispersing the CNCs into a PVAc water emulsion or into a PEG solution in water, followed by solution casting as films and drying [100]. Due to the partial miscibility of PVAc or PEG with PHB and PHBV, they improved the dispersion of the CNCs into the polymer matrix. This was determined by the favorable hydrogen bonding interactions between the hydroxyl groups on the CNCs surface and the polar groups on the PVAc and PEG chains. The addition of a third polymer had as a result an improvement in the mechanical properties, more important in the case of the PVAc-containing nanocomposites. The plasticizing effect of PEG could be a cause of the lower improvement in the mechanical properties observed in the PEG-containing nanocomposites [100].
A combined solvent casting and melt processing technique was used to obtain a good dispersion of CNCs from pine cones in a PHB/poly(ε-caprolactorne) (PCL) blend [101]. CNCs were dispersed in chloroform and were added in a mixture of PHB/PCL (75:25) in chloroform under intense stirring. The solvent casted films were melt-compounded in a twin screw microextruder and compression molded. Nanocomposites with a content of CNCs of 3, 5 and 7 wt% were obtained by this method. In low amounts, CNCs enhanced the compatibility between the immiscible PHB and PCL and reduced their phase separation during the melt blending. This was due to the tendency of CNCs to locate at the PHB - PCL interface preventing the coalescence of the dispersed PCL phase in the continuous PHB matrix during the melt processing. The best dispersion of CNCs in the PHB/PCL matrix was obtained for a CNCs content of 3 wt%. In this case, the nanocomposite showed a significant increase in transparency that can be attributed to the good dispersion of CNCs and their compatibilization effect, which increased the PHB-PCL miscibility [101].
Poly(lactic acid) (PLA) and CNCs were added in a PHB plasticized with epoxidized canola oil (eCO) to improve its mechanical properties [102]. The PHB/PLA/eCO/CNCs nanocomposites with a PHB:PLA weight ratio of 3:1 and 5 wt% CNCs (related to the PHB/PLA amount) were obtained by melt-mixing using a conical twin-screw micro-extruder. The eCO green plasticizer was added to increase the flexibility and thermal stability of PHB, both important drawbacks of this biopolymer. The concomitant addition of PLA and eCO proved to be beneficial to both the elastic properties and thermal stability of nanocomposites [102].
A melt compounding masterbatch technique was applied to obtain PLA/PHB/CNCs nanocomposite films plasticized with a low content of acetyl tributyl citrate [103]. In addition to being an easily scalable and environmentally friendly technique, the melt compounding masterbatch technique ensured a good dispersion of the CNCs and plasticizer in the PLA/PHB blend. This technique consists in the fabrication of a PHB masterbatch, containing both the plasticizer and the CNCs, and its further dilution in PLA, both phases comprising melt compounding operations. The addition of 5 wt% CNCs to the plasticized PLA/PHB matrix led to an increase in the storage modulus due to the stiffening effect of the CNCs and the good dispersion of the high aspect ratio CNCs in the polymer matrix [117].

References

  1. Thirumala, M.; Vishnuvardhan, R.S.; Mahmood, S.K. Production and characterization of PHB from two novel strains of Bacillus spp. isolated from soil and activated sludge. J. Ind. Microbiol. 2010, 37, 271–278.
  2. Surendran, A.; Lakshmanan, M.; Chee, J.Y.; Sulaiman, A.M.; Thuoc, D.V.; Sudesh, K. Can polyhydroxyalkanoates be produced efficiently from waste plant and animal oils? Front. Bioeng. Biotechnol. 2020, 8, 169.
  3. Tang, X.; Chen, E.Y.-X. Chemical synthesis of perfectly isotactic and high melting bacterial poly(3-hydroxybutyrate) from bio-sourced racemic cyclic diolide. Nat. Commun. 2018, 9, 2345.
  4. Portugal-Nunes, D.J.; Pawar, S.S.; Lidén, G.; Gorwa-Grauslund, M.F. Effect of nitrogen availability on the poly-3-d-hydroxybutyrate accumulation by engineered Saccharomyces cerevisiae. AMB Express 2017, 7, 35.
  5. Dilkes-Hoffman, L.S.; Lant, P.A.; Laycock, B.; Pratt, S. The rate of biodegradation of PHA bioplastics in the marine environment: A meta-study. Mar. Pollut. Bull. 2019, 142, 15–24.
  6. Barkoula, N.M.; Garkhail, S.K.; Peijs, T. Biodegradable composites based on flax/polyhydroxybutyrate and its copolymer with hydroxyvalerate. Ind. Crops Prod. 2010, 31, 34–42.
  7. McAdam, B.; Brennan Fournet, M.; McDonald, P.; Mojicevic, M. Production of polyhydroxybutyrate (PHB) and factors impacting its chemical and mechanical characteristics. Polymers 2020, 12, 2908.
  8. Santos, A.; Dalla Valentina, L.V.O.; Schulz, A.; Duarte, M.A.T. From obtaining to degradation of PHB: Material properties. Part I. Ing. Cienc. 2017, 13, 269–298.
  9. Raza, Z.A.; Khalil, S.; Abid, S. Recent progress in development and chemical modification of poly(hydroxybutyrate)-based blends for potential medical applications. Int. J. Biol. Macromol. 2020, 160, 77–100.
  10. de Carvalho, A.J.; das Graças Silva-Valenzuela, M.; Wang, S.H.; Valenzuela-Diaz, F.R. Biodegradable nanocomposite microcapsules for controlled release of urea. Polymers 2021, 13, 722.
  11. Râpă, M.; Zaharia, C.; Stănescu, P.O.; Cășărică, A.; Matei, E.; Predescu, A.M.; Pantilimon, M.C.; Vidu, R.; Predescu, C.; Cioflan, H. In vitro degradation of PHB/bacterial cellulose biocomposite scaffolds. Int. J. Polym. Sci. 2021, 3820364.
  12. Panaitescu, D.M.; Vizireanu, S.; Stoian, S.A.; Nicolae, C.-A.; Gabor, A.R.; Damian, C.M.; Trusca, R.; Carpen, L.G.; Dinescu, G. Poly(3-hydroxybutyrate) modified by plasma and TEMPO-oxidized celluloses. Polymers 2020, 12, 1510.
  13. Bugnicourt, E.; Cinelli, P.; Lazzeri, A.; Alvarez, V. Polyhydroxyalkanoate (PHA): Review of synthesis, characteristics, processing and potential applications in packaging. Express Polym. Lett. 2014, 8, 791–808.
  14. Ma, P.; Cai, X.; Chen, M.; Dong, W.; Lemstra, P.J. Partially bio-based thermoplastic elastomers by physical blending of poly(hydroxyalkanoate)s and poly(ethylene-co-vinyl acetate). Express Polym. Lett. 2014, 8, 517–527.
  15. Leroy, E.; Petit, I.; Audic, J.L.; Colomines, G.; Deterre, R. Rheological characterization of a thermally unstable bioplastic in injection molding conditions. Polym. Degrad. Stab. 2021, 97, 1915–1921.
  16. Cesário, M.T.; Raposo, R.S.; de Almeida, M.C.M.D.; van Keulen, F.; Ferreira, B.S.; da Fonseca, M.M. Enhanced bioproduction of poly-3-hydroxybutyrate from wheat straw lignocellulosic hydrolysates. New Biotechnol. 2014, 31, 104–113.
  17. Bedade, D.K.; Edson, C.B.; Gross, R.A. Emergent approaches to efficient and sustainable polyhydroxyalkanoate production. Molecules 2021, 26, 3463.
  18. Reddy, M.V.; Mawatari, Y.; Onodera, R.; Nakamura, Y.; Yajima, Y.; Chang, Y.C. Bacterial conversion of waste into polyhydroxybutyrate (PHB): A new approach of bio-circular economy for treating waste and energy generation. Bioresour. Technol. Rep. 2019, 113, 456–460.
  19. Sayyed, R.Z.; Shaikh, S.S.; Wani, S.J.; Rehman, M.T.; Al Ajmi, M.F.; Haque, S.; El Enshasy, H.A. Production of biodegradable polymer from agro-wastes in Alcaligenes sp. and Pseudomonas sp. Molecules 2021, 26, 2443.
  20. Soto, L.R.; Byrne, E.; van Niel, E.W.J.; Sayed, M.; Villanueva, C.C.; Hatti-Kaul, R. Hydrogen and polyhydroxybutyrate production from wheat straw hydrolysate using Caldicellulosiruptor species and Ralstoniaeutropha in a coupled process. Bioresour. Technol. 2019, 272, 259–266.
  21. Van Thuoc, D.; Chung, N.T.; Hatti-Kaul, R. Polyhydroxyalkanoate production from rice straw hydrolysate obtained by alkaline pretreatment and enzymatic hydrolysis using Bacillus strains isolated from decomposing straw. Bioresour. Bioprocess. 2021, 8, 98.
  22. Pagliano, G.; Gugliucci, W.; Torrieri, E.; Piccolo, A.; Cangemi, S.; Di Giuseppe, F.A.; Robertiello, A.; Faraco, V.; Pepe, O.; Ventorino, V. Polyhydroxyalkanoates (PHAs) from dairy wastewater effluent: Bacterial accumulation, structural characterization and physical properties. Chem. Biol. Technol. Agric. 2020, 7, 29.
  23. Dalsasso, R.R.; Pavan, F.P.; Bordignon, S.E.; de Aragão, G.M.F.; Poletto, P. Polyhydroxybutyrate (PHB) production by Cupriavidusnecator from sugarcane vinasse and molasses as mixed substrate. Process. Biochem. 2019, 85, 12–18.
  24. Hassan, M.A.; Bakhiet, E.K.; Hussein, H.R.; Ali, S.G. Statistical optimization studies for polyhydroxybutyrate (PHB) production by novel Bacillus subtilis using agricultural and industrial wastes. Int. J. Environ. Sci. Technol. 2018, 16, 3497–3512.
  25. Gonzalez, A.; Iriarte, M.; Iriondo, P.J.; Iruin, J.J. Miscibility and carbon dioxide transport properties of blends of bacterial poly(3-hydroxybutyrate) and a poly(vinylidene chloride-co-acrylonitrile) copolymer. Polymer 2002, 43, 6205–6211.
  26. Eraslana, K.; Aversab, C.; Nofarac, M.; Barlettab, M.; Gisariod, A.; Salehiyane, R.; Goksu, Y.A. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH): Synthesis, properties, and applications—A review. Eur. Polym. J. 2022, 67, 111044.
  27. Jian, Y.; Zhu, Y. Poly 3-hydroxybutyrate 4-hydroxybutyrate (P34HB) as a potential polymer for drug-eluting coatings on metal coronary stents. Polymers 2022, 14, 994.
  28. Naser, A.Z.; Deiab, I.; Darras, B.M. Poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHAs), green alternatives to petroleum-based plastics: A review. RSC Adv. 2021, 11, 17151–17196.
  29. Ibrahim, M.I.; Alsafadi, D.; Alamry, K.A.; Hussein, M.A. Properties and applications of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biocomposites. J. Polym. Environ. 2021, 29, 1010–1030.
  30. Nosal, H.; Moser, K.; Warzała, M.; Holzer, A.; Stańczyk, D.; Sabura, E. Selected fatty acids esters as potential PHB-V bioplasticizers: Effect on mechanical properties of the polymer. J. Polym. Environ. 2012, 29, 38–53.
  31. Frone, A.N.; Nicolae, C.A.; Eremia, M.C.; Tofan, V.; Ghiurea, M.; Chiulan, I.; Radu, E.; Damian, C.M.; Panaitescu, D.M. Low molecular weight and polymeric modifiers as toughening agents in poly(3-hydroxybutyrate) films. Polymers 2020, 12, 2446.
  32. Popa, M.S.; Frone, A.N.; Panaitescu, D.M. Polyhydroxybutyrate blends: A solution for biodegradable packaging? Int. J. Biol. Macromol. 2022, 207, 263–277.
  33. Garcia-Garcia, D.; Ferri, J.M.; Boronat, T.; Lopez-Martinez, J.; Balart, R. Processing and characterization of binary poly(hydroxybutyrate) (PHB) and poly(caprolactone) (PCL) blends with improved impact properties. Polym. Bull. 2016, 73, 3333–3350.
  34. Jakić, M.; Vrandečić, N.S.; Erceg, M. Thermal degradation of poly(3-hydroxybutyrate)/poly(ethylene oxide) blends: Thermogravimetric and kinetic analysis. Eur. Polym. J. 2016, 81, 376–385.
  35. Ma, P.; Hristova-Bogaerds, D.G.; Lemstra, P.J.; Zhang, Y.; Wang, S. Toughening of PHBV/PBS and PHB/PBS blends via in situ compatibilization using dicumyl peroxide as a free-radical grafting initiator. Macromol. Mater. Eng. 2012, 297, 402–410.
  36. Vale Iulianelli, G.C.V.; dos David, G.S.; dos Santos, T.N.; Sebastião, P.J.O.; Tavares, M.I.B. Influence of TiO2 nanoparticle on the thermal, morphological and molecular characteristics of PHB matrix. Polym. Test. 2018, 65, 156–162.
  37. Silva, M.B.R.; Tavares, M.I.B.; Junior, A.W.M.; Neto, R.P.C. Evaluation of intermolecular interactions in the PHB/ZnO nanostructured materials. J. Nanosci. Nanotechnol. 2016, 16, 7606–7610.
  38. Liao, H.-T.; Wu, C.-S. Poly(3-hydroxybutyrate)/multi-walled carbon nanotubes nanocomposites: Preparation and characterizations. Des. Monomers Polym. 2013, 16, 99–107.
  39. Jandas, P.J.; Prabakaran, K.; Kumar, R.; Mohanty, S.; Nayak, S.K. Eco-friendly poly(hydroxybutyrate) nanocomposites: Preparation and characterization. J. Polym. Res. 2021, 28, 285.
  40. Panaitescu, D.M.; Nicolae, C.A.; Gabor, A.R.; Trusca, R. Thermal and mechanical properties of poly(3-hydroxybutyrate) reinforced with cellulose fibers from wood waste. Ind. Crops Prod. 2020, 145, 112071.
  41. Panaitescu, D.M.; Frone, A.N.; Chiulan, I.; Nicolae, C.A.; Trusca, R.; Ghiurea, M.; Gabor, A.R.; Mihailescu, M.; Casarica, A.; Lupescu, I. Role of bacterial cellulose and poly (3-hydroxyhexanoate-co-3-hydroxyoctanoate) in poly (3-hydroxybutyrate) blends and composites. Cellulose 2018, 25, 5569–5591.
  42. Kaur, J.; Sengupta, P.; Mukhopadhyay, S. Critical review of bioadsorption on modified cellulose and removal of divalent heavy metals (Cd, Pb, and Cu). Ind. Eng. Chem. Res. 2022, 61, 1921–1954.
  43. Gan, I.; Chow, W.S. Antimicrobial poly(lactic acid)/cellulose bionanocomposite for foodpackaging application: A review. Food Packag. Shelf Life 2018, 17, 150–161.
  44. Tanpichai, S.; Boonmahitthisud, A.; Soykeabkaew, N.; Ongthip, L. Review of the recent developments in all-cellulose nanocomposites: Properties and applications. Carbohydr. Polym. 2022, 286, 119192.
  45. Louis, A.C.F.; Venkatachalam, S. Energy efficient process for valorization of corn cob as a source for nanocrystalline cellulose and hemicellulose production. Int. J. Biol. Macromol. 2020, 163, 260–269.
  46. Guo, Y.; Zhang, Y.; Zheng, D.; Li, M.; Yue, J. Isolation and characterization of nanocellulose crystals via acid hydrolysis from agricultural waste-tea stalk. Int. J. Biol. Macromol. 2020, 163, 927–933.
  47. Neto, W.P.F.; Silvério, H.A.; Dantas, N.O.; Pasquini, D. Extraction and characterization of cellulose nanocrystals from agro-industrial residue–soy hulls. Ind. Crop. Prod. 2013, 42, 480–488.
  48. Melikoglu, A.Y.; Bilek, S.E.; Cesur, S. Optimum alkaline treatment parameters for the extraction of cellulose and production of cellulose nanocrystals from apple pomace. Carbohydr. Polym. 2019, 215, 330–337.
  49. Coelho, C.C.S.; Michelin, M.; Cerqueira, M.A.; Gonçalves, C.; Tonon, R.V.; Pastrana, L.M.; Freitas-Silva, O.; Vicente, A.A.; Cabral, L.M.C.; Teixeira, J.A. Cellulose nanocrystals from grape pomace: Production, properties and cytotoxicity assessment. Carbohydr. Polym. 2018, 192, 327–336.
  50. Prado, K.S.; Spinacé, M.A.S. Isolation and characterization of cellulose nanocrystals from pineapple crown waste and their potential uses. Int. J. Biol. Macromol. 2019, 122, 410–416.
  51. Souza, A.G.; Santos, D.F.; Ferreira, R.R.; Pinto, V.Z.; Rosa, D.S. Innovative process for obtaining modified nanocellulose from soybean straw. Int. J. Biol. Macromol. 2020, 165, 1803–1812.
  52. Frone, A.N.; Chiulan, I.; Panaitescu, D.M.; Nicolae, C.A.; Ghiurea, M.; Galan, A.-M. Isolation of cellulose nanocrystals from plum seed shells, structural and morphological characterization. Mater. Lett. 2017, 194, 160–163.
  53. Fortunati, E.; Benincasa, P.; Balestra, G.M.; Luzi, F.; Mazzaglia, A.; Del Buono, D.; Puglia, D.; Torre, L. Revalorization of barley straw and husk as precursors for cellulose nanocrystals extraction and their effect on PVA_CH nanocomposites. Ind. Crops Prod. 2016, 92, 201–217.
  54. Kallel, F.; Bettaieb, F.; Khiari, R.; García, A.; Bras, J.; Chaabouni, E.S. Isolation and structural characterization of cellulose nanocrystals extracted from garlic straw residues. Ind. Crops Prod. 2016, 87, 287–296.
  55. Jiang, F.; Hsieh, Y.-L. Cellulose nanocrystal isolation from tomato peels and assembled nanofibers. Carbohydr. Polym. 2015, 122, 60–68.
  56. Ferreira, F.V.; Mariano, M.; Rabelo, S.C.; Gouveia, R.F.; Lona, L.M.F. Isolation and surface modification of cellulose nanocrystals from sugarcane bagasse waste: From a micro- to a nano-scale view. Appl. Surf. Sci. 2018, 436, 1113–1122.
  57. Hideno, A.; Abe, K.; Yano, H. Preparation using pectinase and characterization of nanofibers from orange peel waste in juice factories. J. Food Sci. 2014, 79, N1218–N1224.
  58. Nagalakshmaiah, M.; Mortha, G.; Dufresne, A. Structural investigation of cellulose nanocrystals extracted from chili leftover and their reinforcement in cariflex-IR rubber latex. Carbohydr. Polym. 2016, 136, 945–954.
  59. Pennells, J.; Godwin, I.D.; Amiralian, N.; Martin, D.J. Trends in the production of cellulose nanofibers from non-wood sources. Cellulose 2020, 27, 575–593.
  60. Dhali, K.; Ghasemlou, M.; Daver, F.; Cass, P.; Adhikari, B. A review of nanocellulose as a new material towards environmental sustainability. Sci. Total Environ. 2021, 775, 145871.
  61. Salimi, S.; Sotudeh-Gharebagh, R.; Zarghami, R.; Chan, S.Y.; Yuen, K.H. Production of nanocellulose and its applications in drug delivery: A critical review. ACS Sustain. Chem. Eng. 2019, 7, 15800–15827.
  62. Pradhan, D.; Jaiswal, A.K.; Jaiswal, S. Emerging technologies for the production of nanocellulose from lignocellulosic biomass. Carbohydr. Polym. 2022, 285, 119258.
  63. Wang, L.; Li, K.; Copenhaver, K.; Mackay, S.; Lamm, M.E.; Zhao, X.; Dixon, B.; Wang, J.; Han, Y.; Neivandt, D.; et al. Review on nonconventional fibrillation methods of producing cellulose nanofibrils and their applications. Biomacromolecules 2021, 22, 4037–4059.
  64. Noremylia, M.B.; Hassan, M.Z.; Ismail, Z. Recent advancement in isolation, processing, characterization and applications of emerging nanocellulose: A review. Int. J. Biol. Macromol. 2022, 206, 954–976.
  65. Trache, D.; Hussin, M.H.; Haafiz, M.K.M.; Thakur, V.K. Recent progress in cellulose nanocrystals: Sources and production. Nanoscale 2017, 9, 1763–1786.
  66. Briassoulis, D.; Tserotas, P.; Athanasoulia, I.-G. Alternative optimization routes for improving the performance of poly (3-hydroxybutyrate) (PHB) based plastics. J. Clean. Prod. 2021, 318, 128555.
  67. Frone, A.N.; Panaitescu, D.M.; Donescu, D.; Spataru, C.I.; Radovici, C.; Trusca, R.; Somoghi, R. Preparation and characterization of PVA composites with cellulose nanofibers obtained by ultrasonication. Bioresources 2011, 6, 487–512.
  68. Mohammad Taib, M.N.A.; Hamidon, T.S.; Garba, Z.N.; Trache, D.; Uyama, H.; Hussin, M.H. Recent progress in cellulose-based composites towards flame retardancy applications. Polymer 2022, 244, 124677.
  69. Teodoro, K.B.R.; Sanfelice, R.C.; Migliorini, F.L.; Pavinatto, A.; Facure, M.H.M.; Correa, D.S. A review on the role and performance of cellulose nanomaterials in sensors. ACS Sens. 2021, 6, 2473–2496.
  70. Vatansever, E.; Arslan, D.; Nofar, M. Polylactide cellulose-based nanocomposites. Int. J. Biol. Macromol. 2019, 137, 912–938.
  71. Panaitescu, D.M.; Lupescu, I.; Frone, A.N.; Chiulan, I.; Nicolae, C.A.; Tofan, V.; Stefaniu, A.; Somoghi, R.; Trusca, R. Medium chain-length polyhydroxyalkanoate copolymer modified by bacterial cellulose for medical devices. Biomacromolecules 2017, 18, 3222–3232.
  72. Seoane, I.T.; Cerrutti, P.; Vazquez, A.; Manfredi, L.B.; Cyras, V.P. Polyhydroxybutyrate-based nanocomposites with cellulose nanocrystals and bacterial cellulose. J. Polym. Environ. 2017, 25, 586–598.
  73. Panaitescu, D.M.; Frone, A.N.; Chiulan, I. Nanostructured biocomposites from aliphatic polyesters and bacterial cellulose. Ind. Crops Prod. 2016, 93, 251–266.
  74. Siró, I.; Plackett, D. Microfibrillated cellulose and new nanocomposite materials: A review. Cellulose 2010, 17, 459–494.
  75. Zhang, B.; Huang, C.; Zhao, H.; Wang, J.; Yin, C.; Zhang, L.; Zhao, Y. Effects of cellulose nanocrystals and cellulose nanofibers on the structure and properties of polyhydroxybutyrate nanocomposites. Polymers 2019, 11, 2063.
  76. Jun, D.; Guomin, Z.; Mingzhu, P.; Leilei, Z.; Dagang, L.; Rui, Z. Crystallization and mechanical properties of reinforced PHBV composites using melt compounding: Effect of CNCs and CNFs. Carbohydr. Polym. 2017, 168, 255–262.
  77. Kampeerapappun, P. The electrospunpolyhydroxybutyrate fibers reinforced with cellulose nanocrystals: Morphology and properties. J. Appl. Polym. Sci. 2016, 133, 43273.
  78. Panaitescu, D.M.; Popa, M.S.; Raditoiu, V.; Frone, A.N.; Sacarescu, L.; Gabor, A.R.; Nicolae, C.A.; Teodorescu, M. Effect of calcium stearate as a lubricant and catalyst on the thermal degradation of poly(3-hydroxybutyrate). Int. J. Biol. Macromol. 2021, 190, 780–791.
  79. Frone, A.N.; Batalu, D.; Chiulan, I.; Oprea, M.; Gabor, A.R.; Nicolae, C.A.; Raditoiu, V.; Trusca, R.; Panaitescu, D.M. Morpho-structural, thermal and mechanical properties of PLA/PHB/cellulose biodegradable nanocomposites obtained by compression molding, extrusion, and 3D printing. Nanomaterials 2020, 10, 51.
  80. Panaitescu, D.M.; Trusca, R.; Gabor, A.R.; Nicolae, C.A.; Casarica, A. Biocomposite foams based on polyhydroxyalkanoate and nanocellulose: Morphological and thermo-mechanical characterization. Int. J. Biol. Macromol. 2020, 164, 1867–1878.
  81. Dhar, P.; Vangala, S.P.; Tiwari, P.K.; Kumar, A.; Katiyar, V. Thermal degradation kinetics of poly (3-hydroxybutyrate)/cellulose nano- crystals based nanobiocomposite. J. Thermodyn. Catal. 2014, 5, 1000134.
  82. Dhar, P.; Bhardwaj, U.; Kumar, A.; Katiyar, V. Poly (3-hydroxybutyrate)/cellulose nanocrystal films for food packaging applications: Barrier and migration studies. Polym. Eng. Sci. 2015, 55, 2388–2395.
  83. Ten, E.; Bahr, D.F.; Li, B.; Jiang, L.; Wolcott, M.P. Effects of cellulose nanowhiskers on mechanical, dielectric, and rheological properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhisker composites. Ind. Eng. Chem. Res. 2012, 51, 2941–2951.
  84. Seoane, I.T.; Fortunati, E.; Puglia, D.; Cyras, V.P.; Manfredi, L.B. Development and characterization of bionanocomposites based on poly(3-hydroxybutyrate) and cellulose nanocrystals for packaging applications. Polym. Int. 2016, 65, 1046–1053.
  85. Seoane, I.T.; Cerrutti, P.; Vazquez, A.; Cyras, V.P.; Manfredi, L.B. Ternary nanocomposites based on plasticized poly(3-hydroxybutyrate) and nanocellulose. Polym. Bull. 2019, 76, 967–988.
  86. Seoane, I.T.; Luzi, F.; Puglia, D.; Cyras, V.P.; Manfredi, L.B. Enhancement of paperboard performance as packaging material by layering with plasticized polyhydroxybutyrate/nanocellulose coatings. J. Appl. Polym. Sci. 2018, 135, 46872.
  87. Seoane, I.T.; Manfredi, L.B.; Cyras, V.P.; Torre, L.; Fortunati, E.; Puglia, D. Effect of cellulose nanocrystals and bacterial cellulose on disintegrability in composting conditions of plasticized PHB nanocomposites. Polymers 2017, 9, 561.
  88. de O. Patrício, P.S.; Pereira, F.V.; dos Santos, M.C.; de Souza, P.P.; Roa, J.P.B.; Orefice, R.L. Increasing the elongation at break of polyhydroxybutyrate biopolymer: Effect of cellulose nanowhiskers on mechanical and thermal properties. J. Appl. Polym. Sci. 2013, 127, 3613–3621.
  89. Ten, E.; Turtle, J.; Bahr, D.; Jiang, L.; Wolcott, M. Thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhiskers composites. Polymer 2010, 51, 2652–2660.
  90. Chen, J.; Xu, C.; Wu, D.; Pan, K.; Qian, A.; Sha, Y.; Wang, L.; Tong, W. Insights into the nucleation role of cellulose crystals during crystallization of poly(β-hydroxybutyrate). Carbohydr. Polym. 2015, 134, 508–515.
  91. Kampeerapappun, P. Extraction and characterization of cellulose nanocrystals produced by acid hydrolysis from corn husk. J. Met. Mater. Miner. 2015, 25, 19–26.
  92. Choi, J.; Kang, J.; Yun, S.I. Nanofibrous foams of poly(3-hydroxybutyrate)/cellulose nanocrystal composite fabricated using nonsolvent-induced phase separation. Langmuir 2021, 37, 1173–1182.
  93. Seoane, I.T.; Manfredi, L.B.; Cyras, V.P. Bilayer biocomposites based on coated cellulose paperboard with films of polyhydroxybutyrate/cellulose nanocrystals. Cellulose 2018, 25, 2419–2434.
  94. Jiang, L.; Morelius, E.; Zhang, J.; Wolcott, M.; Holbery, J. Study of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhisker composites prepared by solution casting and melt processing. J. Compos. Mater. 2008, 42, 2629–2645.
  95. Magnani, C.; Idström, A.; Nordstierna, L.; Müller, A.J.; Dubois, P.; Raquez, J.M.; Lo Re, G. Interphase design of cellulose nanocrystals/poly(hydroxybutyrate-ran-valerate) bionanocomposites for mechanical and thermal properties tuning. Biomacromolecules 2020, 21, 1892–1901.
  96. Yu, H.Y.; Qin, Z.Y.; Yan, C.F.; Yao, J.M. Green nanocomposites based on functionalized cellulose nanocrystals: A study on the relationship between interfacial interaction and property enhancement. ACS Sustain. Chem. Eng. 2014, 2, 875–886.
  97. Jo, J.; Kim, H.; Jeong, S.-Y.; Park, C.; Hwang, H.S.; Koo, B. Changes in mechanical properties of polyhydroxyalkanoate with double silanized cellulose nanocrystals using different organosiloxanes. Nanomaterials 2021, 11, 1542.
  98. Oksman, K.; Mathew, A.P.; Bondeson, D.; Kvien, I. Manufacturing process of polylactic acid (PLA)—cellulose whiskers nanocomposites. Compos. Sci. Technol. 2006, 66, 2776–2784.
  99. Chen, J.; Wu, D.; Tam, K.C.; Pan, K.; Zheng, Z. Effect of surface modification of cellulose nanocrystal on nonisothermal crystallization of poly(β-hydroxybutyrate) composites. Carbohydr. Polym. 2017, 157, 1821–1829.
  100. Pracella, M.; Mura, C.; Galli, G. Polyhydroxyalkanoate nanocomposites with cellulose nanocrystals as biodegradable coating and packaging materials. ACS Appl. Nano Mater. 2021, 4, 260–270.
  101. Garcia-Garcia, D.; Lopez-Martinez, J.; Balart, R.; Strömberg, E.; Moriana, R. Reinforcing capability of cellulose nanocrystals obtained from pine cones in a biodegradable poly(3-hydroxybutyrate)/poly(ε-caprolactone) (PHB/PCL) thermoplastic blend. Eur. Polym. J. 2018, 104, 10–18.
  102. Lopera-Valle, A.; Caputo, J.V.; Leão, R.; Sauvageau, D.; Luz, S.M.; Elias, A. Influence of Epoxidized Canola Oil (eCO) and Cellulose Nanocrystals (CNCs) on the Mechanical and Thermal Properties of Polyhydroxybutyrate (PHB)—Poly(lactic acid) (PLA) Blends. Polymers 2019, 11, 933.
  103. Frone, A.N.; Ghiurea, M.; Nicolae, C.A.; Gabor, A.R.; Badila, S.; Panaitescu, D.M. Poly(lactic acid)/Poly(3-hydroxybutyrate) Biocomposites with Differently Treated Cellulose Fibers. Molecules 2022, 27, 2390.
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Subjects: Materials Science, Biomaterials
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Denis Mihaela Panaitescu
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Catalina Usurelu
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Adriana Nicoleta Frone
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Revisions: 2 times (View History)
Update Date: 20 May 2022
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