HIGH-DENSITY POLYETHYLENE HYDROGENATED OLIGO(CYCLOPENTADIENE) BLENDS - TENSILE STRESS-STRAIN BEHAVIOR

The influence of hydrogenated olio(cyclopentadiene) (HOCP) on tensile mechanical properties of its blends with high density polyethylene (HD PE) has been studied at 20, 80, and 100 degrees C. The nominal stress- strain curves performed at 20 degrees C indicate an increase of the mo dulus and a conspicuous decrease of the ultimate properties increasing the HOCP content in the blend. Blends with HOCP content > 20%-wt are found to be very fragile at 20 degrees C. These behaviors have been re lated to the presence of the HOCP-rich phase that has the glass transi tion at about 55 degrees C. At 20 degrees C the HOCP oligomers act as a hardener for the HDPE. The nominal stress-strain curves performed at 80 and 100 degrees C show a strong decrease of the modulus (compared to the value at 20 degrees C), plastic deformation for all the blends tested, and rupture of HDPE and blend samples at the beginning of the cold-drawing. Moreover, the modulus and the ultimate parameters are fo und to decrease with the composition. The behaviors at 80 and 100 degr ees C have been related to several factors: the higher mobility of HDP E molecules at these temperatures compared to that at 20 degrees C; th e HOCP-rich phase that is at temperatures higher than its glass transi tion, and so it acts as a plasticizer for the HDPE; and the decreases of crystallinity and number of entanglements when the HOCP is added to the HDPE component. (C) 1995 John Wiley and Sons, Inc.