Compaction of ultrahigh-molecular-mass poly(ethylene) reactor powders

The process of ultrahigh-molecular-mass poly(ethylene) (SHMWPE) room-temper ature compaction, representing the first stage in manufacturing high-streng th fibers from the reactor powder (RP) was studied for two SHMWPE samples w ith equal densities, approximately equal molecular masses, and markedly dif ferent powder densities (0.057 vs. 0.206 g/cm(3)). It was established that three sequential deformation processes take place when a powder pellet is c ompressed under increasing pressure in a closed volume. In the first step, the powder particles in a pellet is brought into closer contact and the pel let density increases. Upon reaching a sufficiently large number of contact s, this densification process ceases and the plastic deformation of individ ual grains becomes a dominating process. This very stage features the forma tion of bonds between separate RP grains. As the pressure grows further, th e material density increases due to the elastic deformation; this stage doe s not contribute to the final density and strength of the RP pellet upon th e pressure release. The average pore size and the powder density of the ini tial RP pellets is a critical parameter: the effective compaction under pre ssure takes place for only the RP samples with a powder density below 0.150 g/cm(3).