Search for: All records

Abstract The processing–structure–property relationship using poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET) is explored. Specifically, both pre‐extension and preshear of amorphous PLA and PET above their glass transition temperaturesT_g, carried out in the affine deformation limit, can induce a specific type of cold crystallization during annealing, i.e., nanoconfined crystallization (NCC) where crystal sizes are limited to a nanoscopic scale in all dimensions so as to render the processed PLA and PET optically transparent. The new polymer structure after premelt deformation can show considerably enhanced mechanical properties. For example, premelt stretching produces geometric condensation of the chain network. This structural alternation can profoundly change the mechanical characteristics, e.g., turning brittle PLA ductile. In contrast, after preshear of amorphous PLA aboveT_g, the NCC containing PLA remains brittle, showing the importance to have geometric condensation from processing. Both AFM imaging and SAXS measurements are performed to verify that premelt deformation of PLA and PET indeed results in NCC from annealing that permits the strain‐induced cold crystallization to take place on the length scale of the mesh size of the deformed chain network. 

Abstract This series of publications describes research rendering soft polyisobutylene (PIB)‐based thermoplastic elastomers 3D printable by blending with rigid chemically compatible thermoplastics. The molecular structure, morphology, physical properties, and 3D printability of such blends have been systematically investigated. The authors' first report was concerned with the rendering of soft poly(styrene‐b‐isobutylene‐b‐styrene) (SIBS) 3D printable by blending with rigid polystyrene (PS). Here they report the macromolecular engineering of SIBS/polyphenylene oxide (PPO) blends for 3D printing. PPO, a rigid high‐performance thermoplastic, is compatible with the hard PS block in SIBS; however, neither PPO nor SIBS can be directly 3D printed. The microphase‐separated structures and physical properties of SIBS/PPO blends are systematically tuned by controlling blending ratios and molecular weights. Suitable composition ranges and desirable properties of SIBS/PPO blends for 3D printing are optimized. The morphology and properties of SIBS/PPO blends are characterized by an ensemble of techniques, including atomic force microscopy, small‐angle X‐ray scattering, and thermal and mechanical properties testing. The elucidation of processing‐structure‐property relationship of SIBS/PPO blends is essential for 3D printing and advanced manufacturing of high‐performance polymer systems.