Optimal film content improving mechanical and water absorption properties of oriented cotton stalk-plastic boards

Abstract: Wood plastic composites were widely used in furniture, infrastructure and transportation area and most of them were made of short fiber and plastic powder. In order to use cotton stalk resources effectively and make high performance straw-based composites, this paper presents a potential use of long cotton stalk bundles as matrix and isotactic polypropylene (iPP) film or high density polyethylene (HDPE) film as adhesive for oriented cotton stalk-plastic boards (OCPB). The polydiphenylmethane diisocyanate (PMDI) resin was added to enhance the interfacial bonding between cotton stalks and plastic films. The long cotton stalk bundles were first oven-dried, resinated by PMDI resin and divided into two equal portions, the cotton stalks and plastic films were then stacked to form a mat. The plastic films were placed between the two portions of cotton stalks and on the outside surfaces of the mat. Number of plastic films used was adjusted according to the targeted film content in that panel. The formed mat was then hot-pressed between two steel plates preheated to 185?C, and consolidated to a desired thickness. After reaching the final thickness and maintaining for 10 min, the mat was gradually cooled to room temperature. The pressed panel was then trimmed to a final panel size of 300 mm×300 mm × 10 mm. The tested specimens were made according to the referred standards. The effects of film contents on the properties of OCPB, including modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB), thickness swelling (THS) and water absorption (WA) were evaluated. The properties of OCPB were compared with that of medium density fiberboard (MDF) and particleboard. Significance test of film contents on the properties of composites was evaluated by SPSS. Results showed that the mechanical and water absorption properties of OCPB made of iPP film were better than that of HDPE film. The best mechanical and water absorption properties of the composites were obtained with the use of 15% iPP film, with the MOE, MOR, IB, THS and WA were 60.60 MPa, 5074.4 MPa, 1.48 MPa, 2.53% and 18.60% respectively. The mechanical and water absorption properties of OCPB were better than that of MDF and particleboard at the film content of 15%. The SPSS test showed that film contents had a significant influence on the properties of OCPB. Scanning electron micrographs showed that there was a mechanical interlock structure between cotton stalk fibers and plastic films. The OCPB could be a good alternative as construction materials used in indoor or outdoor environment. The study could also be a reference for the use of agricultural biomass and plastic film as raw materials for the fabrication of wood plastic composites.