Dielectric properties of lignocellulosic materials-polypropylene composites

Composites were made from isotactic polypropylene and lignocellulosic materials derived from hemp and flax plants using moulding and hydraulic pressing techniques. Frequency dependences of the electric permittivity ε ′ and the ac conductivity σac of the composite samples were measured in the fre-quency range from 100 Hz to 13 MHz at room temperature. The linear relationship between the reciprocal relative permittivity (1/ε ′) and the volume fraction of the lignocellulosic material was established. The loading of the polypropylene with the lignocellulosic materials increases the electric permittivity ε ′ and improves the electrical conductivity σac. The effect of temperature (150–450 K) on the dielectric spectrum of polypropylene and the composites was investigated in the frequency range from 100 Hz to 1 MHz. Four dielectric relaxation processes were found in the spectra of the composites: β – ascribed to the local motion of the main polymer chain, βwet – associated with the presence of water, δ – related to the motion of the end groups in the branched polymers and σ – due to the conductivity effect. The dielectric spec-trum of polypropylene does not exhibit anomalies. Key words: polymer matrix composites; lignocellulosic material; electrical properties 1