Surface confinement induced amorphization of polyethylene oxide in high-performance porous polyethylene films

Crystallinity of Amphiphilic PE-b-PEG Copolymers

The crystallinity and the growth rate of crystalline structures of polyethylene glycol and polyethylene blocks in polyethylene-b-polyethylene glycol diblock copolymers (PE-b-PEG) were evaluated and compared to polyethylene and polyethylene glycol homopolymers. Melting and crystallization behaviours of PE-b-PEG copolymers with different molecular weights and compositions are investigated by differential scanning calorimetry (DSC). The polyethylene/polyethylene glycol block ratio of the copolymers varies from 17/83 to 77/23 (weight/weight). The influence of the composition of PE-b-PEG copolymer on the ability of each block to crystallize has been determined. Thermal transition data are correlated with optical polarized microscopy, used to investigate the morphology and growth rate of crystals. The results show that the crystallization of the polyethylene block is closer to the polyethylene homopolymer when the copolymer contains more than 50 wt. % of polyethylene in the copolymer. For PE-b-PEG copolymers containing more than 50 wt. % of polyethylene glycol, the polyethylene glycol block morphology is almost similar to the PEG homopolymer. An important hindrance of each block on the crystallization growth rate of the other block has been revealed.

A Versatile Strategy for the Fabrication of Poly(ethyl methacrylate) Composites

Poly(ethyl methacrylate) (PEMA) is dissolved in ethanol, known to be a non-solvent for PEMA, due to the solubilizing ability of an added bile acid biosurfactant, lithocholic acid (LA). The ability to avoid traditional toxic and carcinogenic solvents is important for the fabrication of composites for biomedical applications. The formation of concentrated solutions of high molecular weight PEMA is a key factor for the film deposition using the dip coating method. PEMA films provide corrosion protection for stainless steel. Composite films are prepared, containing bioceramics, such as hydroxyapatite and silica, for biomedical applications. LA facilitates dispersion of hydroxyapatite and silica in suspensions for film deposition. Ibuprofen and tetracycline are used as model drugs for the fabrication of composite films. PEMA-nanocellulose films are successfully prepared using the dip coating method. The microstructure and composition of the films are investigated. The conceptually new approach developed in this investigation represents a versatile strategy for the fabrication of composites for biomedical and other applications, using natural biosurfactants as solubilizing and dispersing agents.

Elongational Flow Field Processed Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends with Distinct Interlayer Phase for Enhanced Tribological Properties

Herein, we produced a series of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends by elongational-flow-field dominated eccentric rotor extruder (ERE) and shear-flow-field dominated twin screw extruder (TSE) respectively and presented a detailed comparative study on microstructures and tribological properties of UHMWPE/PP by different processing modes. Compared with the shear flow field in TSE, the elongational flow field in ERE facilitates the dispersion of PP in the UHMWPE matrix and promotes the interdiffusion of UHMWPE and PP molecular chains. For the first time, we discovered the presence of the interlayer phase in blends with different processing modes by using Raman mapping inspection. The elongational flow field introduces strong interaction to enable excellent compatibility of UHMWPE and PP and induces more pronounced interlayer phase with respect to the shear flow field, eventually endowing UHMWPE/PP with improved wear resistance. The optimized UHMWPE/PP (85/15) blend processed by ERE displayed higher tensile strength (25.3 MPa), higher elongation at break (341.77%) and lower wear loss of ERE-85/15 (1.5 mg) compared to the blend created by TSE. By systematically investigating the microstructures and mechanical properties of blends, we found that with increased content of PP, the wear mechanism of blends varies from abrasive wear, fatigue wear, to adhesion wear as the dominant mechanism for two processing modes.