Plastics surface preparation cross-linking

Use Lubricants, plasticizers, paint and varnish vehicles, gelling agents, urethane intermediates, adhesives, cross-linking agents, humectants, textile fiber finishes, functional fluids, surface-active agents, dispersants and emulsifiers in foods, pharmaceuticals, cosmetic preparations. 

Treatment of certain polymeric surfaces with excited inert gases greatly improves the bond strength of adhesive joints prepared from these materials. With this technique, called plasma treatment, a low-pressure inert gas is activated by an electrode-less radio-frequency discharge or microwave excitation to produce metastable species which react with the polymeric surface. The type of plasma gas can be selected to initiate a wide assortment of chemical reactions. In the case of polyethylene, plasma treatment produces a strong, wettable, cross-linked skin. Commercial instruments are available that can treat polymeric materials in this manner. Table 7.10 presents bond strength of various plastic joints pretreated with activated gas and bonded with an epoxy adhesive. 

Surface preparation of fluoroplastics can be achieved by a number of methods.h i] The plastic surface can be roughened by blasting with water. Other methods include corona bombardment, cross-linking by activated inert gas species, molten metal alloy treatment, sodium hydride treatment, and sodium etching. The treated layer is at most 1 pm thick and does not alter the bulk properties of the fluoroplastic. Surface... 

Flame Treatment - In adhesive bonding, a surfaee preparation technique in which the plastic is briefly exposed to a flame. Flame treatment oxidizes the surface through a free radical mechanism, introducing hydroxyl, carbonyl, carboxyl, and amide functional groups to a depth of 4-6 nm, and produces chain scissions and some cross-linking. Commonly used for polyolefins, polyacetals, and polyethylene terephthalate, flame treatment increases wettability and interfacial diflfusivity. 

Styrene-butadiene-styrene (SBS) block copolymers are adequate raw materials to produce thermoplastic rubber (TR) soles. SBS contains butadiene domains — soft and elastic and styrene domains - hard and tough. Because the styrene domains act as cross-linking agents in the SBS structure, vulcanization is not necessary to provide dimensional stability. TR rubber soles generally contain polystyrene (to impart hardness), plasticizers, fillers, and antioxidants processing oils can also be added. TR rubber soles have a low surface energy, so to reach proper adhesion to polyurethane adhesive a surface modification is needed. Special adhesives have been developed to avoid surface preparation but they have poor creep resistance. 

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