SUPERIOR TENSILE EXTENSIBILITY OF PETG/PC AMORPHOUS BLENDS INDUCED VIA UNIAXIAL STRETCHING

A simultaneous increase of both stiffness and extensibility ofpoly（ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate） （PETG）/polycarbonate （PC） blends prepared through the slit die extrusion-uniaxial cold stretching process was observed. The stretched sheets have a unique mechanical character that an increased tensile modulus is accompanied by an increased extensibility with increasing the draw ratio. Especially, a sharp increasing of the extensibility is observed for PETG/PC （70/30 wt%） blends at draw ratios between 8.2 and 20.0, where a nine times increase of extensibility is achieved. The mechanism of stretching-induced superior extensibility is investigated via micrograph observation, rheometry and calorimetric analysis. The observed superior extensibility could be tentatively explained by the bridging effect of the PC microfibrils on the crack development during tensile failure.

Recovery of Uniaxially Stretched Amorphous Poly(ethylene terephthalate) Film

Recovery behavior of uniaxially stretched amorphous poly(ethylene terephthalate) (a-PET) film near glass transition temperature (T-g) was studied. A strain recovery curve showed that the recovery was made up of two components each with different relaxation time.

POLYMETHYLMETHACRYLATE FILMS IN THE STATE OF HIGH GLOBAL CHAIN ORIENTATION BUT NEARLY RANDOM SEGMENTAL ORIENTATION

PMMA films in the high global chain orientation and nearly random segmental orientation (GOLR) state were prepared by uni-axially drawing at temperatures 20 similar to 30 degrees C above its glass transition temperature, T-g, and their isotropic and anisotropic properties were studied. Experimental results show that this kind of amorphous state, the GOLR state, is nearly isotropic in optical birefringence, IR-dichroism and X-ray diffraction patterns, but is very anisotropic in behaviors of thermal expansion, solvent-swelling and stress-strain.

AMORPHOUS POLY(ETHYLENE TEREPHTHALATE) FILMS IN THE STATE OF HIGH GLOBAL CHAIN ORIENTATION BUT NEARLY RANDOM SEGMENTAL ORIENTATION

The isotropy or anisotropy in some physical properties of the amorphous poly(ethylene terephthalate) films uniaxially drawn at temperatures above its T-g and then quenched to room temperature have been studied. Experimental results here presented show that this amorphous state of high global chain orientation but nearly random segmental orientation, the GOLR state, is nearly isotropic in refractive indices and Young's modulus for small deformation, while it is very probably anisotropic in thermal conduction and microwave dielectric properties.

Partly Imidized Polyamic Acid and Its Uniaxial Stretched Polyimide Films

Partly imidized polyamic acid（PAA） has been used to prepare high performance polyimide films. The be- haviors of two polyamic acids derived from pyromellitic dianhydride（PMDA）/4,4＇-oxydianiline（ODA） and 3,3＇,4,4＇-biphenyltetracarboxylic diahhydride（BPDA）/paraphenylenediamine（PPD） containing dehydrating agents composed of acetic anhydride and a tertiary amine as the catalyst were investigated. The gel point was dependent on imidization degree in despite of temperature and the molar ratio of catalyst to acetic acid. Imdization content was about 35% for PMDA/ODA and about 22% for BPDA/PPD. The effect of catalyst on imidization possessed an order of triethylamine〉3-methylpyridine〉pyridine〉isoquinoline〉2-methylpyridine. The stretching of the films greatly re- duced the coefficient of linear thermal expansion（CTE） either in the longitudinal direction or transversal direction. Compared to the film from polyamic acid, the partly imidized film had greater stretching ratio, so that the uniaxial stretched polyimide film from partly imidized PAA had higher tensile strength and tensile modulus, but lower elonga- tion in the stretching direction.

Robust Poly(glycolic acid) Films with Crystal Orientation and Reinforcement of Chain Entanglement Network

The inherent brittleness of biodegradable poly(glycolic acid) (PGA) restricts its utilization in the packaging field. Traditional toughening methods usually require additional components accompanied by a sacrifice of strength. In the present work, PGA films with simultaneously enhanced strength and ductility are achieved via “casting-stretching-annealing” technology. The reinforced chain entanglement network of PGA induced by the intense extensional stress and the highly oriented crystals grown and refined during the stretching and annealing process endowed the improved ductility and strength of the PGA films, respectively. The relationships among the stretching process, microstructure and mechanical properties of the PGA films have been systematically investigated. As a result, the PGA film (SA-2) with low stretch ratios exhibits excellent ductility with an increase in elongation at break from 22% to 220% and tensile strength from 56 MPa to 130 MPa. Meanwhile, the PGA film (SA-4) with large stretch ratios features much higher tensile strength (335 MPa) while maintaining good ductility (elongation at break of 66%). In addition, highly oriented crystals result in obvious enhancement of heat resistance and dimensional stability of the PGA films. Therefore, this work provides an effective route to fabricate PGA films with both high strength and ductility which may promote the application of PGA materials.