Structure and properties of PE + TALC polymeric composites
Anna Banasiak, Tomasz Sterzyński Akademia Techniczno-Rolnicza, Wydział Technologii i Inżynierii Chemicznej, ul. Seminaryjna 3, 85-326 Bydgoszcz
Annals 2 No. 3, 2002 pages 126-130
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abstract The influence of mineral filler on the mechanical properties like Young’s modulus, yield strength and shrinkage of polyethylene has been investigated. Low density polyethylene (FABS 23-D022) was used as matrix polymer; for the characteristics see Table 1. Talc as modifying additive (the properties of the filler are shown in Table 2) was dispersed in the polymer matrix. The mixture of polyethylene with talc was homogenised by use of Brabender kneader where the master batch procedure was applied. Consequently, the blends of LDPE with talc as filler, in the composition range between 0.1 and 10 wt.%, were compounded by means of an molten extrusion mixing, using an extruder FAIREX with screw dimensions φ = 35, L/D = 24. To assure a sufficient homogenisation quality of the blends, e.g. a good dispersion of the filler in the LDPE matrix, a double extrusion process was applied for all compositions. Thus, the samples for mechanical tensile tests, with thickness of 3 and 1 mm, were produced by injection moulding using an ARBURG 1300 kN. The longitudinal shrinkage of the injection moulded samples was determined using the length of the mould cave as a basic value. The tensile tests, according to the PN-81/C-89034, were performed using a TIRA Test 2200 universal tensile machine. The measurements of the mechanical properties were realised for samples with various thickness (3 and 1 mm, respectively) as well with different talc - content, between 0 and 10 wt.% (Figs 3 to 5). Significantly higher shrinkage values for samples with thickness of 3 mm, in comparison with 1 mm samples, was noted. In both cases a decrease of shrinkage first for a higher talc concentration was observed (Fig. 1). It was also found that the difference between shrinkage values, for both investigated samples thickness, is strongly related to the talc content (Fig. 2). The addition of the mineral filler to the polyethylene matrix results in a certain decrease of the yield strength, as shown in Figure 3. On the contrary an increase of the Young’s modulus (Fig. 4) for higher talc content in the LDPE matrix was noted. In Figure 5 the variation, both of elongation at break and elongation at yield point, of the polyethylene, as a function of the talc content, is presented. As expected, the talc modification of the polyethylene matrix leads to brittle behaviour of the samples, effect specially visible for a higher talc content. The tensile elongation of samples with 1 mm thickness is significantly lower, in all cases, comparing with that of thickness of 3 mm. The changes of the mechanical properties, of talc modified LDPE, may depend on the interaction between the matrix and the dispersed phase but also may result directly from the processing induced structure modification. Especially, the load bearing effect of talc particles with a plate- like structure and an interfacial bonding existing between the matrix and filler should be considered.