![]() Methods currently used to determine this require the filler to be comminuted by means of ultrasound – but this causes severe degradation of the agglomerates in carbon blacks, and also distorts the distribution of silicas. Recent thinking is that the differences in the aggregate size distributions are particularly responsible for the processing and vulcanization characteristics of the compound. This is particularly true in the case of elastomeric matrices. One key is the shape and size of the primary aggregates, which are largely dependent on the manufacturing process, but the distribution of the particles is also important, which is largely controlled by processing conditions. Reinforcement depends on two features: the number of interactions at the interface between polymer and filler (which is mainly controlled by the low primary particle size in conjunction with the surface activity) and the hydrodynamic effects of particle aggregation and agglomeration (which are linked with shear modulus and hysteresis during dynamic or static deformation). However, in products with a high percentage of dolomite, the magnesium carbonate eventually combines with sulphur dioxide to form water-soluble magnesium sulphate, producing efflorescence. Fortunately, gypsum is virtually insoluble in water and cannot be washed out. For example, an outdoor application with a calcium carbonate-filled compound may have its outer layer converted to calcium sulphide and then to calcium sulphate (gypsum) by the effect of sulphur dioxide in the air. Water-soluble compounds in the filler (such as sodium or potassium salts) may be affected by outdoor exposure, so damaging the performance of the compound. In applications, the same effect may be useful in engineering components, improving heat dissipation and/or producing a thermal expansion closer to that of metal. By improving the heat transfer in the melt, the use of a filler may therefore give a faster set-up when moulding, and so improve the cycle time. 4.1.2 Thermal propertiesįillers usually have a thermal conductivity about 20 times higher than plastics, and the specific heat is about 50%. The high aspect ratio of glass fibres means that they can provide the greatest improvement in mechanical properties. Talc offers many options because it is capable of many different modifications and surface treatments. Fibre-like wollastonite particularly improves the flexural modulus while cube-shaped calcium carbonate can improve both impact strength and modulus. Impact strength and flexural modulus are the mechanical properties that can most be improved by careful selection of mineral fillers, and the shape of the particle is important. John Murphy, in Additives for Plastics Handbook (Second Edition), 2001 4.1 Effect of Fillers 4.1.1 Mechanical properties Large deflection is reached before the final failure when fibre rupture occurs. 3.26(b)) and the compressive surface ( Fig. Delamination along the fibre strands can be observed on both the tensile surface ( Fig. In contrast, laminates with all fibres oriented at ±45° to the specimen length direction show ductile failure, as in compression. 3.26 for a biaxial specimen tested along a fibre direction. This typical failure mode can be observed in Fig. The delamination zone starts at the middle of the specimen where the bending moment is maximum, then propagates outwards until significant fibre rupture occurs at the middle section on the tensile surface. All the laminates tested along a fibre direction show brittle failure, generally by outer ply delamination on a tensile surface. 3.25, exhibit less non-linearity than the tensile and compressive responses. The flexural load–deflection responses, shown in Fig. The flexural strengths of all the laminates tested are significantly higher than their tensile strengths, and are also higher than or similar to their compressive strengths. The flexural modulus is similar to the respective tensile modulus, as reported in Table 3.1.
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