concentrations in 1: 1 blends, maintaining the same UL rating.
Phwtics Compounding, 1993, (Jun/Feb) 3234
Thermoplastic polyurethanes reinforced with glass fibres Glass fibres in thermoplastic ~lyure~~es have a reinforcing effect, i.e. increase stiffness and strength. Thin glass tibres give greater reinforcement than thicker ones. It is apparent that it is the aspect ratio rather than the absolute tibre length which governs the effectivity of the reinforcing action. Glass fibres not only influence the mechanical properties of a composite but also its characteristic thermal parameters; for example, the otherwise low heat distortion temperature of TPU is raised to within a range from 120 to 130°C by an increasing fibre concentration. The glass fibre also plays a dominating part in the thermal expansion of the composite. From a glass fibre content of about 20 wt.-% (v,, = 10 vol. %) upwards, glass fibre reinforced TPU is within a range of thermal expansion which corresponds to that of metals such as steel or aluminium. Therefore glass tibre reinforced TPU offers the best po~ntialities for a low-stress const~~tive composite with metals. Kunststoffe Germun Plastic, 1992, (Dee), 1416
Surface-treated mineral fillers
Advanced fillers, or more properly called ~n~tional mineral fillers, improve certain physical properties of a plastic material. They may increase stiffness, reduce shrinkage and improve dimensional stability. They make applications possible for which the matrix material alone would not be suitable.
The dividing line between fillers and reinforcing additives can be established from the mechanical characteristic data from filled systems: (1) compounding materials which increase the strength of a polymer filler system are called reinforcing materials, and (2) compounding materials which do not increase or actually reduce the strength of a material are referred to as fillers. Another correlated criterion for the classification of such materials is their geometric shape, quantified by the aspect ratio, (ratio of length to diameter): a) particulate media, such as chalk, silica or glass beads with an LID ratio near 1 exhibit predominately a tilling effect, b) fibres with an LID ratio larger than 10 exhibit a reinforcing effect, c) platelets, such as talc, mica or clay with an LID ratio between 1 and 10 are between the above distinct groups and cause very little increase in strength, or none at all. Neuburg silica (Neuburg Kieselererde) exhibits a special structure as a result of its formation as a sediment. it is a natural agglomerate of approximately 70 to 85 wt. - % of particulate weathered silica and 30 to 15 wt.-% of kaolinite consisting of platelets which cannot be separated physically. This material can be processed into a variety of products. All mineral fillers included in this study with the exception of talc were treated with an organosilane coating to intensify the interaction between the surface of the inorganic filler and the organic matrix thus improving the prope~ies of the product. Kunststoffe Gemurn Plastics, 1992, (Dee), 16-18
of chemical coupling agents in glass reinforced polyolef ins European demand for glass-filled reinforced polyole~ns continues to show signi~c~t growth rates. The main drive behind this is materiai replacement within the automotive Ol993 Elsevier Science Publishers Ltd