A conceptual model to understand the correlation between topography and wetting of polypropylene- and polyethylene-based wood–plastic composites

Abstract

Microscopic and physico-chemical methods were used for a comprehensive surface characterization of different extruded polypropylene- and polyethylene-based wood–plastic composite (WPC) formulations. The surfaces were analysed using stereophotogrammetry, high-resolution scandisk confocal microscopy and scanning electron microscopy, resulting in detailed information about the topography and surface morphology. In addition, dynamic water contact angle measurements were carried out to characterize the wettability of the samples. The effects of polymer type, polymer content, additive content and processing method on the resulting topography and wetting were investigated. The correlation between topography and wetting resulted in a conceptual model of WPC surface morphology and wetting, which may be applied to optimize adhesion properties of this composite material.

Effect of raw material composition of wood plastic composites on surface roughness parameters evaluated with a robust filtering method

“…The surface roughness measuring lengths of WPC’s were generally rather short: 4 mm 27 or 12.5 mm. 2,3,5 However, in this research, the specimens (four replicates for each WPC combination) were scanned on tracing lengths of 50 mm, because longer tracing length gave more accurate results. 26 Four profiles were recorded for each specimen, two on each specimen face, so that a total of 16 profiles were available for further evaluation of parameters for each WPC combination.…”

“…The roughness profiles were obtained by filtering each profile by using the robust filter RGRF contained in ISO 16610-31 16 and recommended in the methodology from Gurau et al 26 The cutoff used was 2.5 mm as recommended in previous research of Gurau et al 9,26 and also used by various researchers specifically on WPC surfaces. 2,3,24…”

“…Previous studies reported that surface roughness of WPCs was significantly affected by the type and ratio of the thermoplastic, wood, and additives. 2 –6 However, evaluation of surface roughness in case of wood or any wood-based composite requires a special consideration. It was found that general standard requirements followed by the vast majority of researchers, more likely valid for homogeneous materials as metals, are not applicable for wood.…”

“…Furthermore, researchers generally have used a limited number of roughness parameters, from the ones available in the standards, to evaluate the surface quality, such as Ra 18,19 or Rq 20 or a combination of Ra and Rz . 2,3,6 However, these parameters cannot give a complete picture and interpretation of the surface status. A thorough understanding of the surface condition is needed, especially for composite materials where wood is used in combination with other materials and so introducing a degree of unevenness.…”