Lamellar Formation and Relaxation in Simple Sheared Poly(ethylene terephthalate) by Small-Angle X-ray Scattering

Crystallization of Poly(ethylene terephthalate): A Review

Poly(ethylene terephthalate) (PET) is a thermoplastic polyester with excellent thermal and mechanical properties, widely used in a variety of industrial fields. It is a semicrystalline polymer, and most of the industrial success of PET derives from its easily tunable crystallization kinetics, which allow users to produce the polymer with a high crystal fraction for applications that demand high thermomechanical resistance and barrier properties, or a fully amorphous polymer when high transparency of the product is needed. The main properties of the polymer are presented and discussed in this contribution, together with the literature data on the crystal structure and morphology of PET. This is followed by an in-depth analysis of its crystallization kinetics, including both primary crystal nucleation and crystal growth, as well as secondary crystallization. The effect of molar mass, catalyst residues, chain composition, and thermo-mechanical treatments on the crystallization kinetics, structure, and morphology of PET are also reviewed in this contribution.

Microstructure and Mechanical Properties of Severely Deformed Polypropylene in ECAE (Equal Channel Angular Extrusion) via Routes A and C

Equal channel angular extrusion (ECAE) is a solid-state extrusion process for modifying microstructures via severe plastic deformation without modifying the specimen cross section. In this study, changes in the microstructure and mechanical properties of polypropylene resulting from extrusion orientation route A (no rotation between extrusions) and extrusion orientation route C (a rotation of 180° between extrusions) are investigated using a 90° die-angle tooling outfitted with back pressure. Important differences are reported for the ECAE-induced deformation behavior between the two processing routes. A focus is made on the occurrence of heterogeneous plastic deformations (periodic shear banding and warping) for both routes and the control and inhibition of the plastic instabilities via regulated back pressure and ram velocity. Wide-angle X-ray scattering is carried out to characterize the structural evolution as a function of the processing conditions including route, extrusion velocity and BP application. The mechanical properties of the specimens machined from the ECAE pieces are examined under different loading paths including uniaxial tension/compression and simple shear. Full-field displacements converted to volumetric strains revealed the profound impacts of the processing route on the deformation mechanisms during tensile deformation.

Solid-state extrusion of polymers using simple shear deformation

The review considers the possibilities of new methods of solid-state extrusion of polymers based on the use of deformation schemes that include simple shear - equal-channel angular extrusion, equal-channel multi-angle extrusion and combined extrusion. Information on the evolution of the physico-mechanical properties of glassy, semi-crystalline polymers, polymer blends and composites is given.

To Mimic Mechanical Properties of the Skin by Inducing Oriented Nanofiber Microstructures in Bottlebrush Cellulose-graft-diblock Copolymer Elastomers

Skin is a vital biological defense system that protects the body from physical harm with its unique mechanical properties attributed to the hierarchical organization of the protein scaffold. Developing a synthetic skinlike material has aroused great interest; however, replication of the skin's mechanical response, including anisotropic softness and strain-stiffening, is difficult to achieve. Here, to mimic the mechanical behaviors of skin, a reprocessable bottlebrush copolymer elastomer was designed with renewable and rigid cellulose as backbones; meanwhile, poly(n-butyl acrylate)-b-poly(methyl methacrylate) (PBA-b-PMMA) diblocks were designed as the grafted side chains. The so-made elastomers were subjected to a step-cyclic tensile deformation, by which the internal structures became oriented nanofibers and endowed stress-strain behaviors pretty much similar to those of the real skin. Overall, our research work currently undertaken would be of great importance in the development of a series of biomimetic skinlike polymer materials.

Combination of magnetic and enhanced mechanical properties for copolymer-grafted magnetite composite thermoplastic elastomers

Composite thermoplastic elastomers (CTPEs) of magnetic copolymer-grafted nanoparticles (magnetite, Fe3O4) were synthesized and characterized to generate magnetic CTPEs, which combined the magnetic property of Fe3O4 nanoparticles and the thermoplastic elasticity of the grafted amorphous polymer matrix. Fe3O4 nanoparticles served as stiff, multiple physical cross-linking points homogeneously dispersed in the grafted poly(n-butyl acrylate-co-methyl methacrylate) rubbery matrix synthesized via the activators regenerated by electron transfer for atom transfer radical polymerization method (ARGET ATRP). The preparation technique for magnetic CTPEs opened a new route toward developing a wide spectrum of magnetic elastomeric materials with strongly enhanced macroscopic properties. Differential scanning calorimetry (DSC) was used to measure the glass transition temperatures, and thermogravimetric analysis (TGA) was used to examine thermal stabilities of these CTPEs. The magnetic property could be conveniently tuned by adjusting the content of Fe3O4 nanoparticles in CTPEs. Compared to their linear copolymers, these magnetic CTPEs showed significant increases in tensile strength and elastic recovery. In situ small-angle X-ray scattering measurement was conducted to reveal the microstructural evolution of CTPEs during tensile deformation.

Lamellae evolution of poly(butylene succinate-co-terephthalate) copolymer induced by uniaxial stretching and subsequent heating

The structural evolution of biodegradable poly(butylene succinate-co-terephthalate) copolymer was investigated during the uniaxial stretching and following heating processes via in situ small-angle X-ray scattering.