Poly(vinyl chloride) composites reinforced with wood flour and calcinated halloysite

Hybrid poly(vinyl chloride) composites were prepared by adding calcinated halloysite and wood flour to the PVC matrix by mixing in a molten state. The mechanical (DMTA analysis, tensile strength, strain at break, Young's modulus, hardness and impact strength) and thermal (thermal stability, Vicat softening temperature and heat deflection temperature) properties of the composites were tested. The plastographometric analysis suggests that simultaneous addition of two fillers of different origins to the PVC matrix results in a longer gelation time and higher torque values than those observed for neat PVC. Moreover, the presence of calcinated halloysite in PVC/wood flour composites leads to the rise of weight loss temperature compared to PVC composites with only wood flour. When added to PVC/halloysite composites, wood flour improves their homogeneity by breaking halloysite agglomerates, which ensures approx. 116% better thermal stability (confirmed in the Congo red test) compared to unfilled PVC. The synergistic effect of the fillers used on the mechanical properties is demonstrated by the 14.4% higher stiffness and 22.5% higher tensile strength of the PVC composites containing wood flour and 5 wt% halloysite compared to the material loaded with wood flour only.