High-temperature bulk thermolysis of high density polyethylene was performed to obtain degraded polyethylene, which was then left in an oxygen atmosphere for oxidation reaction at 160 • C at different oxidation times, yielding a series of polyethylene degradation-oxidation products. Using infrared spectroscopy, chemical titration, gel chromatography, and differential scanning calorimetry, the structural changes of the polyethylene degradation-oxidation products were investigated. Hydroxyl, carboxyl, ester, and other functional groups were introduced into the molecular chains of oxidation products, and the number of carboxyl groups sharply increased with increasing oxidation time. The breaking of molecular chains as well as combination reactions, such as esterfication, during the oxidation process lead to decrease of number-average molecular weight (M n ) and increase of both weight-average molecular weight (M w ) and molecular weight distribution, and an initial increase and leveling off of the carboxyl number per molecular chain. It is noteworthy that oxidation occurred primarily near weak bonds, mainly terminal vinyl unsaturations. Thus, compared with degraded polyethylene, the oxidation products showed little changes in the melting and crystallization behaviors; even when the oxidation time was up to 4 hr, the drop in the melting and crystallization temperature was less than 3 • C. These results might lay a foundation for exploring tailored low molecular weight polymers to be used just as they are or after chemical modifications of olefinic functions.

The fracture behavior of polypropylene/ethylene-propylenediene terpolymer (100/8) blends with different microstructure was investigated using the essential work of fracture approach. Ethylene-propylene-diene terpolymer and dicumyl peroxide were mixed in a single-screw extruder at 1408C, and the crosslinking reaction had hardly taken place at this temperature. Then the reactive extrusion of ethylene-propylene-diene terpolymer and polypropylene was performed on a twin-screw extruder at a temperature range of 160-2108C and ethylene-propylene-diene terpolymer was crosslinked in this process. Various crosslinking density of ethylene-propylene-diene terpolymer in polypropylene/ethylene-propylene-diene terpolymer (100/8) blends was obtained by varying the concentration of dicumyl peroxide. With increasing dicumyl peroxide concentration, melt flow rate of the blends gradually increased but the increasing trend was slowed up. The degradation reaction of polypropylene was markedly restrained by adopting such a processing method. From the result of scanning electron microscopy, the size of ethylene-propylene-diene terpolymer particles was reduced and a more uniform particle size distribution was obtained. The existence of polypropylene/ ethylene-propylene-diene terpolymer graft copolymer was demonstrated by differential scanning calorimetry and the negative effect of the graft copolymer on the crystalline rate of polypropylene macromolecules which were Downloaded from grafted onto ethylene-propylene-diene terpolymer chains was validated. The specific essential work of fracture (w e ) increased markedly with increasing dicumyl peroxide concentration for the blends prepared. When the concentration of dicumyl peroxide was 0.3 wt% of ethylene-propylene-diene terpolymer content, the value of w e of the dynamic vulcanized blends was about 165% as that of polypropylene/ethylene-propylene-diene terpolymer simple blends or polypropylene, while the specific plastic work (w p ) was still larger than that of polypropylene.

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The effect of reaction time and mechanical stirring on thermal degradation of high density polyethylene(HDPE) was studied at 350 • C under nitrogen atomosphere in a batch pressure reactor. Changes in molecular weight(MW), molecular weight distribution (MWD), and crystalline behaviors of the degraded products were investigated by gel chromatography (GPC) and differential scanning calorimetry (DSC). It was found that MWD curves all shifted toward lower molecular weight with increasing reaction time, with both the extent of the movement and its Mw showing a rapid initial drop and then leveling off. In a short period of reaction time, the MW, MWD and crystalline behaviors of the degraded products were affected notably by the mechanical stirring. The Mw of the degraded products without stirring was lower than that of products with stirring in the same time, which should be related to the large difference of temperature distributions in the reactor. When the reaction time reached 4 h, the Mw of the degraded products had dropped to about 5 × 10 3 g/mol from about 3 × 10 5 g/mol for the original Mw, and the product did not show the melting and crystallization behaviors of high density polyethylene again.