Recent research at Leeds University has seen the development of a new class of 'self-reinforced' polypropylene sheet. The essence of the process, termed hot compaction, is to take layers of woven oriented polypropylene tapes, and compact them together under suitable conditions of temperature and pressure to form a consolidated, homogeneous sheet. The mechanism for consolidaiton is to melt a small proportion of the skin of each tape, which on cooling recrystallises to form a polypropylene matrix to bind the oriented tapes together. Research has shown that there is a usable processing window where sufficient melted material can be created to bind the woven structure together without losing too much of the original oriented structure. The process can be seen as a way of converting the properties of a highly drawn polypropylene tape into a consolidated sheet.
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