The role of creep damage in glass bead filled high density polyethylene

Abstract

The effect of filled-in rigid particles on the strength, modulus and toughness of polymers has been investigated previously, as has creep damage in short fibre reinforced polyprolylene [1-5]. Rigid filler produces a large turbulence of stress field in matrix, and induces microdamage. It therefore significantly affects the mechanical properties of filled materials. In this letter, the influences of bead fraction and interfacial adhesion on creep behaviour are reported. The testing results show that creep damage plays an important role in the high stress level tests. Commercial high density polyethylene (HDPE), J3, supplied by Beijing Second Chemical Factory was used as the matrix material. The neat HDPE has a melting flow index (MFI) of 1.5 g 10 min -1 for series A and 1.9 g 10 rain -1 for series B. The diameter of the glass beads was 30-40 pro. In the manufacturing process, the glass beads and coupling agents were mixed in the chamber of a high speed mixer, then HDPE powder and treated glass beads were blended in a twin-screw extruder, and the pelleted extmdate was injection moulded into tensile bars. Annealing was carried out to relieve the residual stress in the specimens. The materials of series A are the filled HDPE with different volume fractions of glass beads (Table I). For material series B, glass beads were treated by three kinds of coupling agent to make filled HDPE with different interfacial adhesion. Details of these materials are shown in Table II. It has been indicated previously that excellent interfacial adhesion was obtained in Js [1]. J6 has weak bonding and J4 is intermediate in its bond strength. The geometry of the creep specimens refers to ASTM 638 type A. The dimensions of the gauge length area were 50 m m × 10 mm × 3 mm. Creep tests were carried out on a specially designed creep test machine. Linear voltage differential transformer (LVDT) was used to measure the extension of