Study On Preparation, Properties And Mechanism Of Biomass Packaging Materials Made By Bagasse Pith

The serious pollution originated by disposal of large volume of plastic packages,together with the depletion of petroleum stocks, have prompted to an increasing interest innew natural-based biomass packaging materials design. In this paper, a new biomasscomposite material was prepared based on bagasse pith and corn starch by melting blendmethod, and a new biomass cushion packaging material was prepared based on bagasse pith,magnesium bisulfite spent liquor, and reinforcing silica filler by press-molding process. Thebiomass packaging materials were evaluated in terms of mechanical properties, rheologicalproperties, thermal stability and water absorption. The reinforcement mechanism of bagassepith and fumed silica particles were also analyzed, respectively.Thermoplastic starch (TPS) was prepared with glycerol and urea as mixed plasticizer.X-ray diffractometry demonstrated that TPS could restrain starch retro gradation when themass ratio of glycerol to urea was above1:1. SEM micrographs and rheological curves ofstarch plasticization processing showed good plasticizing effect with increasing urea content.According to the mechanical and processing properties of TPS, the optimum mass ratio ofglycerol to urea was1:1.Bagasse pith/thermoplastic starch (BP/TPS) packaging materials were prepared fromthe matrix of TPS and the reinforcement of bagasse pith by melt processing. The influencesof mixing plasticizers contents, bagasse pith loadings, roller speeds and processingtemperature on the tensile properties and flexural properties were investigated. The optimumprocess conditions were demonstrated as follows: the bagasse pith content of10wt%, themixed plasticizers content of45wt%, the mass ratio of glycerol to urea of1:1, roller speeds of40r/min, and processing temperature of140°C, which achieved that the tensile strength was16.71MPa, the flexural strength was15.18%, elastic modulus was21.91MPa, and flexuralmodulus was1267.55MPa.The influences of bagasse pith (40～60mesh) content on the rheological properties,mechanical properties, thermal stability and water absorption of BP/TPS were analyzed. Theplasticization time and constant torque of mixed blends increased with increasing bagassepith content. Moreover, the tensile strength and flexural strength increased, and the thermal stability improved. Water absorption of TPS increased with the addition of bagasse pith at43%RH, while decreased as RH＞75%. The water absorption of TPS were determined bybagasse pith contents at75%RH. FT-IR and SEM illustrated that the intermolecularhydrogen bondings and strong interfacial interactions were formed in the bagasse pith andTPS, which led to reinforcing effect of bagasse pith.The effects of particle size of bagasse pith on the rheological properties, mechanicalproperties and water absorption of BP/TPS were studied, and a relationship function betweenmaximum torque and particle size was established. The results showed that tensile strengthand elongation at break increased at first and then decreased with decreasing particle size.The maximum value of tensile properties of TPS reinforced by pith (60～100mesh) wereobserved. Flexural strength of BP/TPS increased, while the flexural modulus decreased withdecreasing particle size. With the same bagasse pith loading of10wt%, the water absorptionof TPS increased with the addition of bagasse pith (＞60mesh) at43%RH, while decreasedas RH＞75%.Bagasse pith was pre-treated by different concentrations of NaOH solution at differenttemperatures. The effects of lignin content of bagasse pith on the mechanical properties ofBP/TPS were investigated. The results showed that tensile strength of BP/TPS increased withdecreasing lignin content, and the minimum tensile strength was achieved by BP/TPS with5.38%lignin content. The elongation at break of BP/TPS increased at first and then decreasedwith decreasing lignin content. When the lignin extraction was carried out at30°C, theflexural strength and flexural modulus decreased at first and then increased with decreasinglignin content, and the maximum values were achieved by BP/TPS with12.70%lignincontent, up14%and34%on the values of the untreated bagasse pith/TPS, respectively.A new biodegradable cushion packaging material was prepared based on bagasse pith,magnesium bisulfite spent liquor, and reinforcing silica filler. The effects of bagasse pithcontent, fumed silica loading and BET Surface Area of fumed silica on the apparent densityand static compressive strength of the bagasse pith cushion packaging materials (BPCPMs)were investigated. The SEM image of the BPCPMs revealed that the reinforcement effect offumed silica was the consequence of silica filler-matrix interaction and silica filler-fillerinteractions. The most important factors to affect the properties of BPCPMs were the hydrogen bonds between the molecules of lignosulfonate and silanol groups on the silicasurface and dispersion state of silica particles in the matrix. BPCPMs had good cushioningproperties within a large stress range and can be used for packaging heavy delicate articles.The bio-degradation performance of BP/TPS and BPCPMs were investigated by mouldsdegradation. The results indicated that the degradability rates of BP/TPS were above80%,and the maximum degradability rate of BPCPMS was52%after15days of incubation in amedium of liquid nutrients. These results indicated the biomass packaging materials based onbagasse pith had good bio-degradation performance.