Study of sand-plastic composite using optimal mixture design of experiments for best compressive strength

Abstract

Nowadays Plastic wastes are a major environmental concern and free raw materials that can be converted to useful product. By this study, those free raw materials of waste plastics are collected and recycled to produce sand plastic composite brick (SPCB). SPCB of characteristic similar to conventional sand-cement brick was produced using simple technology of compression molding by melt blending technique. Best possible mixture composition of sand and plastic weight percentage for higher compressive strength is determined using optimum mixture design of experiment (DOE). Using Design Expert software, a quadratic model was setup as function of the Sand-Plastic Composite element weight percentage. The setup model was confirmed experimentally through ANOVA table and fit summary. Diagnostic case statics and graphical representations of the model were also investigated by using adjusted R-Squared, predicted R-Squared, DFFITS and Cook's D graphs. In addition, the effects of sand and plastic weight percentage on compressive strength variation were also studied. Finally, optimum percentage of mixtures of sand and plastic that would yield maximum compressive strength is predicted from analysis of graph. Maximum compressive strength about 4.95 N/mm2 was obtained when the plastic weight percent of 60% (40 wt% LDPE and 20 wt% HDPE) was melt blended with sand weight percent of 40% (25% of sand size of 1.18 mm and 15% of sand size 0.5 mm). When waste plastic content was greater than 70%; it affects the response negatively this was result from the impurities content. Sand has negative effect on compressive strength when its wt. % is greater than 42% this was due to pore created in sample of SPC that result from non-coherent mix of plastic and sand. The authors concluded that, inventions like SPCB from waste plastics have many environmental and cost advantages. So, mixture Design of Experiment can be used as an alternative mixture design method in order to get better mechanical property product of sand plastic composites.