Watersorption - Water absorption of Wood Plastic Composites
Wood Plastic Composites (WPC) are composite materials, consisting of wood particles, a thermoplastically processable matrix as well as some additives. This materials class, which gained increasing interest from industry and research over the last years, shows advantages in terms of processing and cost issues. A major drawback of WPC is the water uptake due to the cellulose incorporated in the composite, which results in reduced dimensional stability, mechanical properties and resistance against biological decay.
The methods for suppressing the water uptake, which are currently available, are painting or coating the composites or the chemical modification of the wood particles themselves via acetylation. These methods show several drawbacks, which exclude such WPC from several applications. With coating a structural part is sealed off against water uptake, but with this method the advantage of easier handling is lost, compared with the usual wood materials. Furthermore, such treatments are expensive in processing, as well as there is a need to repeat this treatment several times over the life cycle, resulting in increased effort for the user. The method of acetylating the wood particles is an effective method of suppressing the water uptake, but this method is very expensive due to the fact that in this process much solvent is involved, which has to be reprocessed, thus denying the cost effectiveness of WPC. Furthermore the acetylation reduces the mechanical properties of the composites. Therefore this method is not paying off anymore for this application.
The aim of the project was to investigate and clarify the mechanisms of water sorption and transport in the composite, and, based on these results, to find methods for treating the wood to suppress the water uptake. The main focus for the treatment methods was on the effectiveness of suppression in combination with good processability and cost effectiveness of the treatment processes. Although the aim of the project was the research about the water sorption mechanisms, there should be the possibility of utilizing the project results for future application.
In the scope of the project many different treatment methods were investigated, where the most promising ones are the thermal treatment as well as the treatments with anhydrides and thermosets. Especially the thermal treatment yields very satisfying results due to the simple application and the relatively low costs. For further reduction of water uptake, both the treatments with anhydrides as well as thermosets are very effective, although one has to pay the higher raw material cost. Nevertheless these are relatively low, due to the low dosages of few percent related to the wood share, and furthermore these treatments will pay off due to the reduction of problems in the different applications.
The results from this project show, that it is possible to reduce the water uptake of WPC with quite simple methods. With that it is possible to use WPC in applications which were not accessible until now due to the water absorption properties of WPC.
Dr. Christoph Burgstaller
Transfercenter für Kunststofftechnik GmbH (TCKT)
Projekt collaborator TCKT
B. Priller, BSc, Ing. A. Gösweiner, Ing. H. Ladner, Ing. K. Moser, C. Hainberger, F. Hartl, C. Maticka
Project or cooperation partners
- Dr. Martin Sonntag
- Dr. K. Fischer, Dr. S. Schmidt, DI (FH) P. Glaser, DI (FH) C. Adler, S. Ikrai, S. Marx-Guschall
- Rehau AG, D