Physical and mechanical properties of foamed HDPE/wheat straw flour/nanoclay hybrid composite

In this study, the effects of Azodicarbonamide (AZD) and nanoclay (NC) content on the physico-mechanical and foaming properties of HDPE/wheat straw flour (WSF) composites were investigated. To meet this objective, AZD as the exothermic chemical foaming agent (CFA) with 3 levels of 0, 2 and 4 phr (per hundred parts of resin) and three NC levels of 0, 2, and 5 phr were used. The amount of WSF was fixed at 40 phr for all formulations. First, the WSF, HPDE, NC and AZD were compounded under the foaming agent decomposing temperature in an internal mixer (HAAKE) and microcellular closed cell foamed samples were prepared using an injection molding machine in a batch foaming process. The cellular structure results showed that by increasing the AZD content from 2 to 4 phr, the average cell size and cell density increased whereas the foam density showed a decrease to 21.7% and by adding NC up to 5 phr, the cell size decreased and the cell density increased. When the contents of the AZD increased from 0 to 4 phr, the water absorption and thickness swelling of samples increased to 19.3% and 26.5% respectively. The mechanical properties of HPDE/WSF composite were reduced by adding the CFA and it was improved by adding 2 phr of NC. It should also be noted that the addition of AZD and NC had a negative effect on the foamed composites impact resistance. These results were further supported by SEM micrographs.