ABSTRACT
The development and characterization of poly(lactic acid)(PLA)/guineacorn (Sorghum bicolor) husks particulates (GHP) composites as biodegradable or green composites was investigated to serve as an alternative to the conventional polymers which are non-degradable and are used for short term periods before discarding. The GHP was treated with Sodium hydroxide (NaOH) solution, 3- Aminopropyltriethoxysilane (3-APS) and a combination of both treatments but the PLA was blended with Biomax Strong 100 and Polyethylene glycol (PEG) as impact modifiers. Four formulations of the composites were produced by firstly melt mixing using extrusion and pelletizing before injection moulding. The GHP was characterized by density measurement, thermogravimetric analysis (TGA) and Scanning Electron Microscopy (SEM). The composites produced were characterized by density measurements and mechanical testing such as tensile, impact, hardness and flexural tests. Others include water absorption test on all the composite formulations to study its effect on the mechanical properties. Soil burial test was used to evaluate the degradation of the composites.Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were used for PLABM/GHP composites. Scanning Electron Microscopy (SEM) was used to studythe morphology of the composites, surfaces of water absorbed and soil buried specimens. The density of GHP lied between 1.45 and 1.46 g/cm3, the TGA showed that GHP had 3-step degradation at 30-100oC, 240-340oC and above 340oC while that of PLABM/GHP showed a one-step degradation and exhibited a maximum degradation temperature of 350oC. The ash contents at 600oC showed an increase with increase in GHP content.The density results of PLAP, PLABM, PLPG and PP and their composites lied between 1.26-1.40 g/cm3,1.28-1.36 g/cm3, 1.29-1.40 g/cm3 and 0.96-1.12 g/cm3 respectively. The results of theirtensile strength and elongation at break showed a general viii decrease with increase in GHP content. The unreinforced matrices exhibited higher tensile strengths with maximum of 57.13MPa, and minimum of 25.88MPa as compared with various composites having a maximum of 45.48MPa and minimum of 16.63MPa. The results of the tensile modulus on the other hand showed a general increase as the GHP content was increased. The tensile modulus for the unreinforced matrices had a maximum of 2294.12MPa for PLAP and a minimum of 733MPa for PP. The morphological study of the tensile fractured surfaces revealed brittle failure for PLA matrices but ductile failure for PP matrix composites. The water absorption test showed a general increase in water absorption as GHP was increased from 0 to 40%. The maximum water absorption for the composites at 40% GHP were 11.36%, 12.46%, 21.12% and 6.8% for PLAP, PLABM, PLPG and PP composites respectively while the unreinforced matrices absorbed water to the tune of 0.53%, 0.92%, 1.93% and 0.3% for PLAP, PLABM, PLPG and PP respectively. The degradation test showed increase with GHP content. The weight losses for the unreinforced matrices were 0.36%, 0.20%, 0.46% and 0.08% for PLAP, PLABM, PLPG and PP respectively while at 40% GHP content for the ALKSIL treated composites, the weight losses were 5.05%, 24.16%, 14.83% and 1.65% for PLAP, PLABM, PLPG and PP composites respectively. The surface morphologies after soil burial revealed significant erosion and deep holes in most of the specimens due to the actions of microorganisms in the soil. From the DSC results, the glass transition temperature (Tg) of PLABM was 60oC and melting temperature (Tm) was 150oC. The storage modulus results showed a general increase with GHP content. The composites produced were light in weight, biodegradable and can be used for products intended for short-term use or indoor applications.
