Impact of multiple recycling on the dimensional stability of wood–plastic composite made by the injection moulding process

ABSTRACT This study explored the effect of multiple recycling on the dimensional stability of wood–plastic composite. For this purpose, the injection moulding parameters effective on dimensional stability were first optimized based on the response surface method. Optical scanning, melt flow index (MFI), and differential scanning calorimetry (DSC) tests were used to analyse the shrinkage and deformation of recycled samples. The obtained results revealed that some recycled samples were subjected to thermal changes during the grinding and injection moulding process. The MFI and DSC results showed that the high-density polyethylene thermoplastic used in the wood–plastic composite was broken with long chains. Also, thermal changes occurred during the grinding and injection moulding process. The samples recycled three times had the highest dimensional instability (2.8% of shrinkage values). Finally, with the reduction of DSC, the semi-crystalline structure changed to amorphous, and the samples recycled four and five times had 2.7% and 2.5% shrinkage percentage, respectively.