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Topic Review

Polypropylene (PP)

Polypropylene (PP) is a semicrystalline polyolefin built from propylene units, whose methyl side groups fix the chain conformation and therefore the tacticity, the crystallinity and the melting point. Isotactic chains pack into a helical lattice, atactic chains stay amorphous, and the balance between the two sets stiffness and toughness. Electrical properties of polypropylene nanocomposites follow from the dispersion of the filler and from the crystallinity of the matrix [1]. Carbon nanomaterials change the structure and the conductivity of the polymer while its processability is retained [2]. Gaseous plasma treatment of non-woven polypropylene alters the surface energy without changing the bulk [3].

6
06 Nov 2026

Topic Review

Interpenetrating Polymer Networks

Interpenetrating polymer networks are combinations of two or more polymer networks that are at least partly interlocked on a molecular scale without being covalently joined [1]. Each network is synthesised or crosslinked in the presence of the other, so the two are entangled and cannot be separated without breaking chemical bonds [1]. The morphology is set by the relative rates of network formation and by the compatibility of the components, which decide whether the phases stay co-continuous or separate into domains [2]. Because the networks carry no bonds between them, the material is classed as a polymer blend rather than a copolymer [3]. Swelling in a common solvent is limited by the elastic restraint each network imposes on the other [2].

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06 Nov 2026

Topic Review

Hollow Fiber Membranes

Hollow fiber membranes are self-supporting tubes with a porous wall, in which the lumen carries one stream and the outer surface the other, so the two are separated by a thin selective skin [1]. The wall is asymmetric: a dense or finely porous layer sits on a sponge-like support with finger voids, and the support carries the pressure load while the skin sets selectivity [1]. Fibers are spun from a polymer dope by phase inversion, and the bore fluid composition, the air gap and the coagulation bath fix the wall structure and the skin thickness [1]. Because the wall is thin, the permeance per unit driving force is high, and a module packs a large area into a small volume [2]. The same geometry is reproduced in chitosan and in conductive diamond, where the wall chemistry rather than the polymer sets the surface interaction [3].

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06 Nov 2026

Topic Review

Polyvinyl Pyrrolidone

Polyvinyl pyrrolidone is a vinyl polymer built from N-vinylpyrrolidone units, in which a lactam ring hangs from each backbone carbon [1]. The amide carbonyl and the ring nitrogen make the polymer a strong hydrogen-bond acceptor and strongly hygroscopic, and the same polarity makes it soluble in water and in alcohols while insoluble in hydrocarbons [2]. Because the lactam is non-ionic, the polymer carries no charge at any pH and its solutions stay stable across the pH range [1]. The ring also complexes iodine and phenolic compounds, and the chain adsorbs onto polar surfaces through the carbonyl oxygen [3]. Molar mass spans several orders of magnitude, and the chain-length grade rather than the chemistry sets the viscosity of a solution [2].

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06 Nov 2026

Topic Review

Solvent-free describes a process or formulation that proceeds without a liquid medium, so that reactants, catalysts or coating components meet as solids, melts or gases [1]. In polymer processing the term covers melt extrusion, solid-state shear and reactive extrusion, where the polymer itself serves as the reaction medium [2]. In organic synthesis it denotes reactions run by grinding, by heating the neat reactants or under microwave irradiation, in which the absence of dilution raises the effective concentration of the reacting groups [2]. Removing the solvent also removes the drying step and the residual-solvent specification, and it takes away the medium that would otherwise dissipate heat or dissolve an intermediate [3].

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06 Nov 2026

Topic Review

Flame-Retardant

Flame-retardant additives and comonomers slow the ignition or the spread of a fire in a polymer. Four general mechanisms are distinguished: gas-phase radical scavenging, condensed-phase char formation, dilution by an inert filler, and physical cooling by an endothermic decomposition [1]. Halogenated compounds act in the gas phase and are efficient at low loading, but their combustion products are corrosive and persistent, which has driven substitution [2]. Phosphorus-based systems favour char and are the main alternative for engineering thermoplastics [3]. Intumescent formulations combine an acid source, a carbon source, and a blowing agent, so the coating expands into a foam that insulates the underlying material [4]. The additive normally degrades the mechanical properties, and the balance between the loading needed for a fire rating and the property loss is the central design problem [5].

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20 Oct 2026

Topic Review

Polymer Degradation

Polymer degradation is the loss of the useful properties of a polymer through a chemical or physical change in its structure, usually involving chain scission or crosslinking. The process is initiated by heat, light, oxygen, mechanical stress, or microorganisms, and the contributions are difficult to separate because they act together in service [1]. Photo-oxidation begins with the absorption of ultraviolet light by a chromophore, either in the backbone or in a residual catalyst, and proceeds through a radical chain reaction [2]. The earliest sign is usually a loss of elongation rather than of strength, so a tensile test on an aged specimen is more sensitive than a spectroscopic measurement [3]. Stabilisers act either by absorbing the ultraviolet light or by trapping the radicals, and the two mechanisms are combined in a commercial package [4]. Predicting a service life requires an accelerated test, and the extrapolation is valid only when the degradation mechanism is unchanged, which is rarely verified [5].

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20 Oct 2026

Topic Review

Thermoplastic Resin

A Thermoplastic Resin is a polymer that softens reversibly on heating and solidifies on cooling, so it can be melted, reshaped and reprocessed without chemical cure [1]. A new liquid thermoplastic resin reinforced with jute fibres forms a bio-composite whose temperature- and frequency-dependent behaviour has been analysed [1]. Press and injection hybrid moulding of carbon fibre-reinforced thermoplastic parts depends on the injection material and the resin layer [2]. Adding thermoplastic resin and composite to epoxy resin toughens the thermoset, lifting mechanical and thermal properties [3]. Introducing single-walled carbon nanotubes into thermoplastic acrylic resin improves the electrical and mechanical properties of carbon fibre laminates [4]. Thermoplastic polyurethane blended with eugenol-based phenoxy resin gains self-healing behaviour through exchange reactions [5].

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23 Oct 2026

Topic Review

An organohydrogel consists of a crosslinked polymer network swollen by a water-organic solvent mixture, or by an organic liquid alone, rather than by water [1]. The organic component lowers the freezing point and the vapour pressure of the liquid phase, so the network stays soft below zero degrees Celsius and retains its mass in open air for longer than a conventional hydrogel [2]. Solvent composition also changes the solubility of the network: a poor solvent contracts the chains and raises modulus, whereas a good solvent swells them and lowers it [1]. Where the two liquids differ in affinity for the polymer, they separate into domains, and that heterogeneity raises toughness because a crack is deflected at the boundary [3]. Ionic conductivity survives in the organic-rich phase, which is why the same network can serve at low temperature [2].

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06 Nov 2026

Topic Review

Polypeptides are polymers of amino acids joined by amide bonds between the carboxyl group of one residue and the amino group of the next [1]. The backbone repeats over three atoms per residue, and the dihedral angles of that backbone decide whether the chain adopts an alpha-helix, a beta-sheet or a random coil [1]. Sequence, and not composition alone, fixes the conformation, so two polymers with identical amino acid content can fold differently [2]. Synthesis proceeds either by stepwise coupling of protected amino acids or by ring-opening polymerisation of N-carboxyanhydrides, and the routes differ in the control they give over sequence and dispersity [3]. The amide bond is cleaved by proteases, which makes the backbone degradable under physiological conditions [2].

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06 Nov 2026

Topic Review

Carbohydrate Polymers

Carbohydrate polymers are macromolecules built from sugar residues joined by glycosidic bonds, and the class spans storage polysaccharides, structural glycans and their synthetic derivatives [1]. Linkage position and anomeric configuration decide whether the chain is linear and ribbon-like, as in cellulose, or branched and compact, as in starch and glycogen [2]. Hydroxyl groups along the backbone make the polymers hydrophilic and able to form extended hydrogen-bond networks, which underlies their gelation and film formation [1]. Because each repeat unit carries several reactive hydroxyls, substitution at a fraction of them yields derivatives whose solubility and charge differ from the parent [1]. Molar mass and degree of substitution, rather than sugar identity alone, set the viscosity of a solution [3].

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06 Nov 2026

Topic Review

The protein corona is the layer of adsorbed proteins that forms on a nanoparticle once it enters a biological fluid [1]. Its composition is set by the abundance of the proteins, by their affinity for the surface and by competitive exchange between them, so the layer evolves from a loosely bound initial state to a more compact and longer-lived one [1]. Surface charge, hydrophobicity and particle curvature decide which proteins bind and how tightly [2]. The corona replaces the engineered surface as the interface that cells encounter, so the biological identity of the particle is the corona rather than the bare material [3]. Because composition depends on the fluid and on exposure time, the corona is described together with the medium and the incubation period [2].

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06 Nov 2026

Topic Review

Hybrid Nanocomposites

A hybrid nanocomposite combines two or more chemically distinct phases, at least one of which has a dimension below one hundred nanometres, so that the interface occupies a large fraction of the total volume [1]. The filler may be inorganic, organic or itself a hybrid, and the property that shifts most is the one governed by the boundary: thermal conductivity, gas sensitivity or stiffness [2]. Because the interfacial area per unit mass grows as the filler shrinks, a loading of a few per cent by volume already changes the response, and the percolation threshold falls as the aspect ratio rises [1]. Biological composites reproduce the same architecture at a larger scale, where mineral platelets in a protein matrix give stiffness without losing toughness [3]. Aggregation of the filler removes the interface the design depends on, so the dispersion state is reported alongside the loading [2].

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06 Nov 2026

Topic Review

Percolation Threshold

The percolation threshold is the filler content at which a dispersed phase first forms a connected path across a matrix, so that a transport property switches from that of the matrix to that of the filler [1]. Below the threshold the filler sits in isolated clusters and conductivity stays negligible; at the threshold the largest cluster spans the sample and the property rises by orders of magnitude [1]. For spherical fillers the threshold is predicted near sixteen volume percent, and it falls sharply as the aspect ratio of the filler rises, which is why nanotubes and graphene reach the transition below one percent [2]. The measured value depends on dispersion and on alignment, since agglomerated or oriented fillers percolate at loadings different from well-dispersed isotropic ones [3]. The transition is sharp in the thermodynamic limit and rounded in a finite specimen [1].

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06 Nov 2026

Topic Review

SBS is a triblock copolymer of styrene, butadiene and styrene in which two glassy polystyrene end blocks are joined by a rubbery polybutadiene middle block [1]. Below the glass transition of polystyrene the end blocks aggregate into domains that act as physical crosslinks, so the material behaves as a vulcanised rubber yet flows when heated above about 100 degrees Celsius [1]. The polybutadiene block carries a double bond in every repeat unit, and that unsaturation is the point of sulfur vulcanisation, of hydrogenation and of graft polymerisation [2]. The same segment oxidises in air and the material yellows as conjugated carbonyl groups accumulate [3]. Commercial grades differ in styrene-to-butadiene ratio and in block molecular weight, and those two variables fix modulus, hardness and melt viscosity [1].

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06 Nov 2026

Topic Review

SEBS is a triblock copolymer of styrene, ethylene-butylene and styrene in which glassy polystyrene end blocks anchor a rubbery midblock [1]. The midblock is a hydrogenated polybutadiene segment, so the chain carries no double bonds and resists oxidation and ultraviolet exposure better than the unsaturated parent [1]. The polystyrene domains act as physical crosslinks that hold the network at room temperature and soften above the glass transition of polystyrene, so the material is thermoplastic and reprocessable [2]. The styrene-to-rubber ratio fixes modulus and melt viscosity, while the midblock length sets elasticity [1]. Because the junctions are physical, the polymer dissolves in non-polar solvents without breaking covalent bonds [3].

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06 Nov 2026

Topic Review

Polyaniline (PANI)

Polyaniline is a conjugated polymer of repeated aniline units whose oxidation state and protonation set its electronic character [1]. The chains exist as leucoemeraldine, emeraldine or pernigraniline according to the ratio of reduced to oxidised units, and only the emeraldine salt, protonated by an acid, is electrically conductive [1]. Conduction proceeds by polaron hopping along the protonated backbone and between chains, so it depends on doping level and on chain packing rather than on molar mass [2]. The polymer is insoluble in most solvents in its conducting form, while the emeraldine base dissolves in some organic acids [3]. Its absorption spectrum shifts with oxidation state, which gives the colour changes that track the doping level [3].

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06 Nov 2026

Topic Review

Star polymers are branched macromolecules in which several linear arms radiate from a single central node [1]. The node may be a small molecule, a crosslinked microgel or the residue of a multifunctional initiator, and its functionality fixes the number of arms [1]. Because the arms crowd the core, chain conformation departs from that of a linear polymer of equal molar mass, and the arm number enters the hydrodynamic radius and the melt viscosity [1]. A microgel core with polyelectrolyte arms gives a species that swells and contracts as a whole [2]. Star-block and miktoarm variants carry arms of different chemistry on the same node, so incompatible segments are held in one molecule [3].

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06 Nov 2026

Topic Review

Polyether Ether Ketone

Polyether ether ketone is a semi-crystalline aromatic thermoplastic whose repeat unit joins para-substituted phenyl rings through ether and ketone linkages [1]. The aromatic backbone gives chemical resistance and a high continuous service temperature, while the crystallinity of about thirty per cent fixes stiffness and the amorphous phase governs toughness [1]. The polymer melts near 343 degrees Celsius, keeps a glass transition at about 143 degrees, dissolves only in strong acids, and is sulfonated by concentrated sulfuric acid at the ring [1]. Carbon or glass fibre raises modulus and creep resistance and reduces the mismatch in thermal expansion with metal [2]. Because the elastic modulus approaches that of cortical bone, the unfilled polymer is examined as an implant material, although its bioinert surface bonds weakly to tissue [3].

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06 Nov 2026

Topic Review

Microbeads are solid, approximately spherical particles with diameters between one micrometre and one millimetre, distinguished from irregular powders by sphericity and a narrow size distribution rather than by composition [1]. Glass grades are drawn and milled, while polymer microbeads are produced by emulsion, suspension or dispersion polymerisation, in which monomer droplets or swollen particles set into spheres [2]. Diameter, density and surface chemistry are the defining descriptors, since buoyancy in water and retention on a filter both follow from them [3]. Particles of this size range are classed with microplastics when the polymer resists degradation, and that persistence separates them from mineral or glass beads of equal diameter [3]. Encapsulation of a colloidal core within a polymeric bead adds an internal phase without changing the outer geometry [2].

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06 Nov 2026

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