Effect of screw-disc extrusion process on the level of microbiological contamination of wood-plastic composites (WPC)

The article presents the results of an analysis of the effect of the screw-disc extrusion process on the microbiological quality of WPC composites. The research material consisted of components used for the manufacture of wood-plastic composites in a form of flour, and chips from two kinds of trees (deciduous and coniferous), as well as the PP granulate and composites obtained from them. The study was conducted in two stages. Stage I involved determining the microbiological contamination level in the components used for wood-plastic composite manufacturing.Stage II involved an examination of the microbiological purity of the final composites. The composites under examination were in two forms, i.e. rods and plates.The composites were obtained using a screw-disc extruder and molds for plate compression. The microbiological examinations were conducted according to the standard PN-EN ISO 21527-1:2009. It was observed as a result of the analysis performed that the wood waste used for the production of wood-plastic composites demonstrated strong microbiological contamination, unlike the original polymer material used in the composites matrix. Irrespective of the kinds and forms of the chips used (tree species, degree of pulverization and share), the applied extrusion parameters (temperature and pressure) caused the sterilization of the obtained composites. It may be concluded that the problems presented in the literature,related to an occurrence of molds and fungi on WPC elements used outside, are the result of secondary contamination