Polymer mechanical grinding

Powdered crystalline samples can also be studied by XRD. The sample is loaded onto the specimen holder, which is placed in the X-ray beam in a setup similar to that used for single crystal XRD. The sample must be powdered by hand or by mechanical grinding and is pressed into a sample holder to form a flat surface or packed into a thin glass or polymer capillary tube. After mounting, the specimen is rotated relative to the X-ray source at a rate of (degrees 0)/min. Diffracted radiation comes from the sample according to the Bragg equation. The detector is simultaneously rotated at 20/min. 

By rolling on a two-roll mill the molecular weight of the polymer can be greatly reduced by mechanical scission, analogous to that involved in the mastication of natural rubber, and so mouldable materials may be obtained. However, bulk polymerisation is expensive and the additional milling and grinding processes necessary make this process uneconomic in addition to increasing the risk of contamination. 

Mechanical recycling, the most realistic way used by almost all the plastic manufacturers shredding and grinding of polymer scraps allow a partial re-use in the original application but the recyclate level is low because of the decrease in performance. An extension of this principle is obtained by manufacturing other parts of lower performance, sometimes in another industry. 

Grinding or milling causes degradation of many polymers. The process of mastication of natural rubber involves a mechanically initiated, autoxidative degradation which lowers the molecular weight to a level where the material is easier to process on a commercial scale. 

Mechanochemical Degradation. Mechanochemical degradation occurs in polymers as the result of an applied mechanical force. This type of degradation is quite common in machining processes such as grinding, ball milling, and mastication. 

Deters (14) vibromilled a blend of cellulose and cellulose triacetate. The acetic acid content of cellulose acetate decreased with grinding time (40 h) while that of the cellulose increased, suggesting the formation of a block or graft copolymer or of an esterification reaction by acetic acid developed by mechanical reaction. Baramboim (/5) dissolved separately in CO polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). After mixing equal volumes of solutions of equivalent polymer concentration, the solvent was evaporated at 50° C under vacuum and the resultant product ball-milled. The examination of the ball-milled products showed the formation of free radicals which copolymerized. 

Thus, macroradicals have been obtained by stretching fibers (20), deforming plastics by compression (37), ball mill grinding (11), freezing and grinding of polymer solutions (10), ultrasonic irradiation (I), mastication (19), dispersion in a microblender (25), and other mechanical techniques (36). Many reviews on the formation of macroradicals by degradative processes have also been published (5, 12,13,16, 33). 

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