Mechanical properties of polypropylene composites filled with the straw of oilseed rape infested by the fungal pathogen Sclerotinia sclerotiorum

Abstract

Considerable quantities of residual oilseed rape straw are available as lignocellulosic fillers in composites of thermoplastic polymers. Composites manufactured from polypropylene filled with crushed oilseed rape straw have favourable mechanical properties and increased sound absorption. Unfortunately, the straw of oilseed rape is frequently infested with the fungal pathogen Sclerotinia sclerotiorum, which causes sclerotinia stem rot. In studies carried out so far no attempts have been made to investigate effects of colonising microbes on the suitability of plants as a source of lignocellulose. The aim of this paper was to compare mechanical properties of polypropylene composites containing straw of oilseed rape with and without plant infestation by S. sclerotiorum. In order to obtain composites, parenchyma was removed from oilseed rape straw, which was subsequently ground to 1–2 mm sized particles and then, the technique of extrusion and injection moulding was employed with the addition of 30% of infested plant material using two winter oilseed rape (Brassica napus L.) cultivars of different genetic backgrounds and plant growing habits. The following parameters were determined: maximal tensile strength, elongation at maximal strain, strength and elongation at rupture, strain at plasticity limit 0.2%, Young modulus, Izod impact strength as well as Brinell’s impact test. The performed investigations revealed that composites with the addition of the straw of oilseed rape infested with S. sclerotiorum had mechanical parameters comparable to those recorded in samples filled with healthy lignocellulosic material. It allows the application of plant fillers without the necessity of selection of straw obtained in field conditions.