Abstract
It has been discovered that Spectra® fiber can shift its peak melting temperature upward by almost 10 if it is maintained at constant length. Based on this, a novel processing method called high-temperature, high-pressure sintering has been developed in which Spectra® cloth is consolidated using heat and pressure to make a matrix-free fiber-reinforced composite. Because of the outstanding properties of the Spectra® fiber, the resulting product is a high modulus, high strength, and high-impact resistant ‘one-polymer composite.’ The three key processing parameters are temperature, time, and pressure. The high temperature is in the vicinity of the fiber’s normal melting point so as to induce adequate, but not excessive melting, which allows for the fusion of the cloths on recrystallization. Time is important in the sense of facilitating heat transfer and promoting interfiber and interlayer adhesion while conserving the fiber’s high crystallinity and orientation. The high pressure exerted laterally on the cloths is required to constrain them and prevent shrinkage, as well as eliminate the voids and consolidate the materials. The very long relaxation time and the rubbery nature of ‘melted ultrahigh molecular weight polyethylene’ retard the loss of orientation, and thus make this process possible. The influence of these parameters on the structure and properties of the consolidated structures are studied. Specifically, the crystallinity changes for specimens processed under different conditions are measured by DSC; the molecular orientation changes for specimens processed under different conditions are studied by WAXD; and the impact properties for specimens processed under different conditions are measured by instrumented puncture impact tests. The established process-structure-property relationship is used as a guideline to fine-tune and optimize the processing conditions in order to achieve the best possible impact properties.
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