| The development and application of zein as bio-composites attract more and more attention. Lots of new bio-composites based on zein are developed, such as zein films. However, the physical and mechanical properties are relatively poor compared with traditional petroleum-based products, and their performance is affected by environmental conditions greatly. Therefore, developing effective ways for the utilization of zein has become one of the important research subjects. This study used zein and bamboo powder to generate the composites, discussed the influence of the high pressure on adhesion properties, theological properties, thermal characteristics and micro-structure of zein. Meanwhile, this research explored the inflence of bamboo particle sizes and different NaOH aqueous solution concentrations on mechanical properties of composites, and finally invested the influence of process parameters, such as:moisture content of slab, molding temperature and time on mechanical properties of composites. The results were summarized as the following:(1) With the increase of the pressure (100,200,300,400,500,600 MPa), the modulus of rupture (MOR), modulus of elasticity (MOE) and tensile strength (TS) of composites first increased, and then decreased, when the pressure was 400 MPa, the adhesion properties reached their highest values of 28.4 MPa,2752.58 MPa,15.7 MPa respectively; 2h thickness swelling (2h-ts) of composites first decreased, and then increased, when the pressure was 500 MPa,2h-ts reached their lowest values of 5.6%.(2) The zein solutions with high pressure treatment showed pseudoplastic fluid characteristic, with shear thinning phenomenon. As the pressure increased, the viscosity of solution first increased, and then decreased, and increased again, when the pressure was 400 MPa, the viscosity of solution reached the highest value. With the shear temperature increased, the viscosity of solution first decreased, and then increased, and reached the lowest value at 40℃. With the shear rate increased, the viscosity of solution reduced, and reached a plateau when the shear rate was close to 100 s-1. Zein powder were treated under 400 MPa pressure, denaturation temperature Tm increased and the thermal stability of zein improved; Heat enthalpy△H decreased, the hydrophobic properties and aggregation extent of protein molecules changed; The width of DSC melting peak under high pressure treatment broadened, proving the coordination of zein structure became lower. SEM showed that zein particles under 400 MPa pressure treatment condensed in ring or chain structure.(3) When bamboo particle size was 60 mesh, MOR and MOE of composites reached the highest value of 28.72 MPa and 2669.75 MPa; TS of composites reached the highest value of 17.5 MPa with 40mesh bamboo particle size.2h-ts of composites got the lowest value of 5.8% with 80 mesh bamboo particle size. With the increase of the NaOH aqueous solution concentrations (1%,2%,3%,5% and 10%), MOR and MOE of composites first increased, and then decreased. The value of MOR reached the highest of 28.84 MPa with 2% NaOH aqueous solution treatment on bamboo powder. The highest MOE value of composites was 2913.03 MPa with 3% NaOH aqueous solution treatment. The best TS of composites was obtained with 2% NaOH aqueous solution treatment, the value was 14.5 MPa. The lowest value of 2h-ts of composites was 6.78% with 1% NaOH aqueous solution treatment.(4) When the moisture content of slab (X1) was 14%, molding temperature (X2) was 175℃, molding time (X3) was 12 min. MOR (Y1) and MOE (Y2) of composites achieved maximum value of 31.86 MPa and 3139.36 MPa respectively; When the moisture content of slab (X1) was 14%, molding temperature (X2) was 170℃, molding time (X3) was 15 min, TS (Y3) of composites achieved maximum value of 15 MPa; When the moisture content of slab (X1) was 16%, molding temperature (X2) was 170℃, molding time (X3) was 5 min,2h-ts (Y4) of composites achieved lowest value of 11%. |
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