Study on processing of ultrahigh molecular weight polyethylene/polypropylene blends

Abstract

ABSTRACT:The processing of ultrahigh molecular weight polyethylene (UHMWPE) by the addition of polypropylene (PP) and high-density polyethylene (HDPE) was investigated. The results show that the addition of PP improves the processability of UHMWPE more effectively than does the addition of HDPE. UHMWPE/PP blends can be effectively processed with a twin-roller and general single-screw extruder. In the extrusion of UHMWPE/PP blends, PP is enriched at the surface of the blend adjacent to the barrel wall, thus increasing the frictional force on the wall; the conveyance of the solid down to the channel can then be carried out. The melt pool against the active flight flank exerts a considerable pressure on the UHMWPE powder in the passive flight flank, which overcomes the hard compaction of UHMWPE. The PP penetrates into the gaps between the particles, acting as a heat-transfer agent and adhesive, thus enhancing the heat-transfer ability in the material.

Metastable region of phase diagram: optimum parameter range for processing ultrahigh molecular weight polyethylene blends

“…When χ is in the range of 9.0×10 -3 ∼ 4.1×10 -3 , no UHMWPE is located in the NMWP rich phase, which prevents the viscosity of NMWP from increasing. However, there is a significant amount of NMWP in the UHMWPE rich phase, which favors the swelling of UHMWPE powders [16,17]. When χ is lower than 3.7×10 -3 , interfacial thickness markedly increases with decreasing χ.…”

“…Some unfavorable properties, nevertheless, also existed in the UHMWPE/NMWP blends when homogeneous phase morphologies occur. In the UHMWPE/HDPE blend, for instance, HDPE rich phase could not be distinguished and a homogeneous phase appeared in the crystal morphologies of the blend [16]. The molten HDPE rapidly penetrated into the UHMWPE domains during processing because of the good miscibility of the two polymers.…”

“…According to Takeshi S, Liu GD and others, some NMWP like LDPE and PP can conveniently and effectively reduce the viscosity of UHMWPE as well as retain or even enhance its mechanical properties [15][16][17][18]. Unfortunately, most other NMWP may cause a marked decrease in some of its desirable properties such as izod notched impact strength [19].…”

“…Due to the thick interfaces of the UHMWPE/NMWP blends, there was no substantial decrease of its excellent mechanical properties such as tensile strength and impact strength [15]. Similarly, in the UHMWPE/PP blend, the molten PP preferred to flow into the gaps between UHMWPE particles instead of wholly penetrating into the UHMWPE particles [16,17]. Consequently, the addition of PP significantly improved the melt flowability of UHMWPE and the die pressure was very stable during extrusion.…”

The Sliding Wear of Polypropylene and Its Blends

“…1. 9 The smaller particles are aggregates of yet smaller, sub-micron particles. Some fibrillar bridges exist between these submicron particles in the structure of UHMWPE.…”