As one of the five major engineering plastics, polyamide brings many benefits to humans in the fields of transportation, clothing, entertainment, health, and more. However, as the production of polyamide increases year by year, the pollution problems it causes are becoming increasingly severe. This article reviews the current recycling and treatment processes of polyamide, such as chemical, mechanical, and energy recovery, and degradation methods such as thermal oxidation, photooxidation, enzyme degradation, etc. Starting from the synthesis mechanism of polyamide, it discusses the advantages and disadvantages of different treatment methods of polyamide to obtain more environmentally friendly and economical treatment schemes. Finding enzymes that can degrade high-molecular-weight polyamides, exploring the recovery of polyamides under mild conditions, synthesizing environmentally degradable polyamides through copolymerization or molecular design, and finally preparing degradable bio-based polyamides may be the destination of polyamide.

Strong and tough poly(vinyl alcohol) (PVA)/alginate hydrogen-bonded-ionic dual-physical double-network (DN) hydrogels have been successfully prepared by a facile route of a freeze–thaw (25–25–25 °C) cycle followed by concentrated (1.0 mol L⁻¹ of) aqueous-Ca²⁺ immersion of PVA/Na alginate (SA) mixed aqueous solutions. It was found that, at mole ratios of the PVA- to SA repeat units of 20/1 to 80/1, the DN gels likely evolved a semi-interpenetrating polymer network (IPN) morphology of rigid alginate networks dispersed in while interlocking with ductile PVA network to accomplish DN synergy that gave their high strength and toughness, where the high alginate rigidity originated probably from its dense cross-link induced syneresis and dispersion along crosslink-defective voids to result in little internal stress concentration. Tentatively mechanistically, as the 20/1–80/1 DN gels were stretched steadily, their mechanical response was gradually differentiated into distinct synergistic states: the sparsely hydrogen-bonded PVA served as a ductile matrix to bear small fractions of the established stresses at its large elongations; whereas the densely ionically (i.e. Ca²⁺) cross-linked alginate functioned as a rigid skeleton to sustain the remaining larger stresses upon its smaller local strains. Promisingly, this ductile-rigid matrix-skeleton synergistic mechanism of semi-IPN morphology may be universally extended to all A/B DN hydrogels of large A–B rigidity (or cross-link density) contrast, whether the cross-link nature of network(s) A or B is covalent, ionic, hydrogen bonded or van der Waals interacted. The strong and tough DN gels also displayed satisfactory self-recovery of viscoelastic behaviour, in that their Young's modulus and dissipated energy in the uniaxial tensile mode and dynamic storage and loss moduli in the oscillatory shear mode all recovered significantly from non-linear viscoelastic regimes despite different degrees of failure to revert to (quasi)linear viscoelasticity.

This review discusses the physical-, chemical recycling and biodegradation processes and mechanisms of PET, proposing effecting compromise between its overall properties and conferred intrinsic biodegradability by modified monomer polymerisation.

3,3,3-Trifluoropropylmethyldimethoxysilane (TMDMS) was successfully grafted to molecules of an epoxy resin (EPR) of bisphenol-A origin with an epoxy value of 0.440, i.e. EP44, by transesterification (i.e. alcoholysis) of the TMDMS methoxyls with the EP44 hydroxyls under anhydrous dibutyltin-dilaurate catalysis. Meanwhile, a nanosilica powder was modified with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) via electrophilic substitution of the nanosilica hydroxyls by the HMDS trimethylsilyls to significantly decrease its surface hydroxyls for controlled aggregation. Six coatings, onto an NaOH solution-treated tinplate substrate, of EP44, of the TMDMS-grafted EP44, and of the composites of the TMDMS-grafted EP44 filled with 0.5, 1, 3 and 5 wt% of the HMDS-modified nanosilica were then step-cured mildly with an amino-terminated polyamide from a solution. Owing to the introduction of superhydrophobic trifluoropropyls possibly plus a reduction in the hydrophilic hydroxyl concentration present, the hydrophobicity, evaluated by the water contact-angle, of the EP44 coating increased considerably upon its TMDMS grafting, which then changed little with further addition of the nanosilica. Electrochemical impedance spectroscopy data and simulations revealed that the anticorrosive performance of the TMDMS-grafted EP44 coating, upon immersion into an NaCl solution, was significantly improved compared with the EP44 coating, primarily due to its remarkably enhanced hydrophobic barrier to the water-mediated corrosives (water, NaCl, oxygen, other molecules and ions, etc.). However, the anticorrosion behaviour of the composite coatings was dominated by a corrosion inhibition (i.e. physical barrier) mechanism by the nanosilica filling the pores (free volumes, voids, cracks, etc.) susceptible to the corrosives. As the nanosilica content steadily was raised from 0 to 5 wt%, the corrosion inhibition of the composite coatings first intensified, probably thanks to an enhancement of the filling rate of the pores, and subsequently weakened, presumably due to an increase in the porosity from increased size exclusion of aggregated nanoparticles, and finally improved again possibly owing to a densification of the outside-of-pore barriers of greatly aggregated, size excluded particles, which constituted dual critical concentrations (DCCs) of the nanosilica at 0–0.5 and ∼3 wt%, respectively, that gave rise to a maximum followed by a minimum in the corrosion inhibition. To our knowledge, this has been the first work reporting this unique DCCs behaviour for EPR/nanosilica coatings, which, dictated by a hydrophobic EPR matrix of small porosity as well as a modified nanosilica of controlled aggregation, may universally be extended to the corrosion inhibition of other polymer/nanoceramic coatings.