高分子材料与应用（英文版） Chapter 3 Engineering Plastics.pptVIP

Modified PPO (Noryl) 1. PPO/PS 2. PPO/PA 3. PPO/PPS 4. PPO/PBT 5. PPO/ABS PPO uses Used to replace stainless steel for surgical equipment Replace thermosets Pump housings Valve components Video terminal housings Thermoplastic Polyesters (PET/PBT) Polyester History 1929 W. H. Carothers suggested classification of polymers into two groups, condensation and addition polymers. Carothers was not successful in developing polyester fibers from linear aliphatic polyesters due to low melting point and high solubility. No commercial polymer is based on these. p-phenylene group is added for stiffening and leads to polymers with high melting points and good fiber-forming properties, e.g., PET. Polymers used for films and for fibers Polyesters is one of many heterochain thermoplastics, which has atoms other than C in the chain. Polyesters includes unsaturated (thermosets), saturated and aromatic thermoplastic polyesters. Thermoplastic Polyesters (PET/PBT) Synthesis Thermoplastic Polyester General Family Characteristics PET Higher mechanical stiffness Strength by orienting chains not by H-bonding Get 50% crystallinity forced by mechanical stretching PBT crystallizes rapidly processes faster lower overall properties PET Chemical Structure and Applications The flexible, but short, (CH2)2 groups tend to leave the chains relatively stiff and PET is notes for its very slow crystallization. If cooled rapidly from the melt to a Temp below Tg, PET solidifies in amorphous form. If PET is reheated above Tg, crystallizaiton takes place to up to 30%. In many applications PET is first pre-shaped in amorphous state and then given a uniaxial (fibers or tapes) or biaxial (film or containers) crystalline orientation. During Injection Molding PET can yield amorphous transparent objects (Cold mold) or crystalline opaques objects (hot mold) PBT Chemical Structure and Applications The longer, more flexible (CH2)4 groups allow for more rapid crystallization than PET. PBT is not as conveniently