Optimization of response surface methodology and performance of oxidized wheat straw/polylactic acid composites
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摘要: 为解决麦秸纤维/聚乳酸(WF/PLA)复合材料界面相容性较差的问题,以H2O2作为氧化剂处理麦秸,采用响应面试验法探究H2O2的pH、处理温度、质量比对氧化麦秸纤维(OWF)/PLA复合材料力学性能的影响,得到各因素对复合材料力学性能的影响规律。结果表明:pH和处理温度、pH和质量比、处理温度和质量比之间均表现出明显的交互作用。回归方程预测的最佳工艺参数如下:H2O2的pH为8.9,H2O2的处理温度为52.3℃,H2O2的质量比为2%。在此条件下,复合材料的拉伸强度和断裂伸长率分别为38.89 MPa和7.85%,较未改性前分别提高了15.64%和15.20%。FTIR结果表明,OWF中的部分羟基被H2O2氧化为羧基。SEM结果表明,OWF能够更好地与PLA进行结合,经过熔融共混后制备的复合材料之间具有更好的界面相容性。此外,XRD和DSC结果表明,H2O2的加入促进了聚合物的异相成核过程,使其结晶度有所提高。Abstract: To solve the problem of poor interfacial compatibility of wheat straw fiber/poly(lactic acid) (WF/PLA) composites, WF was treated with H2O2 as oxidant, and the effects of pH, treatment temperature, and mass ratio of H2O2 on the mechanical properties of oxidized wheat straw fiber (OWF)/PLA composites were investigated by response surface method. The results show that there is a significant interaction between pH and treatment temperature, pH and mass ratio, and treatment temperature and mass ratio. The optimal process parameters predicted by the regression equation are as follows: The pH of H2O2 is 8.9, the treatment temperature of H2O2 is 52.3℃, and the mass ratio of H2O2 is 2%. Under these conditions, the tensile strength and elongation at break of the composite material are 38.89 MPa and 7.85% respectively, which are 15.64% and 15.20% higher than before modification. FTIR results indicate that some hydroxyl groups in OWF are oxidized to carboxyl groups by H2O2. SEM results indicate that OWF can better bind with PLA, and the composite materials prepared after melt blending have better interfacial compatibility. In addition, XRD and DSC results indicate that the addition of H2O2 promotes the heterogeneous nucleation process of the polymer, resulting in an increase in its crystallinity.
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表 1 Box-Behnken因素水平表
Table 1. Factors and levels table for Box-Behnken
Level Factor A: pH of H2O2 B: Treatment temperature/℃ C: Mass ratio of H2O2/% −1 7.0 40 2 0 8.0 50 3 1 9.0 60 4 Notes: Total mass of polylactic acid (PLA) blended with wheat straw fiber (WF) is 100%, the mass ratio of H2O2 refers to its proportion to the mass of WF. 表 2 响应面法优化OWF/PLA复合材料拉伸性能试验的设计与结果
Table 2. Design and results of tensile properties test of OWF/PLA composites optimized by response surface method
Run Factors Tensile strength/MPa A B/℃ C/% 1 7.0 40 3 38.69±0.57 2 9.0 40 3 34.61±2.75 3 7.0 60 3 34.43±0.98 4 9.0 60 3 36.09±1.38 5 7.0 50 2 40.80±0.81 6 9.0 50 2 37.84±1.67 7 7.0 50 4 37.76±0.72 8 9.0 50 4 37.83±1.07 9 8.0 40 2 37.54±1.80 10 8.0 60 2 37.05±1.63 11 8.0 40 4 37.86±1.32 12 8.0 60 4 34.20±1.17 13 8.0 50 3 39.02±0.65 14 8.0 50 3 39.41±1.78 15 8.0 50 3 39.21±2.75 16 8.0 50 3 38.97±2.03 17 8.0 50 3 39.04±1.21 表 3 响应面法优化OWF/PLA复合材料力学性能实验中回归方程的方差分析
Table 3. Variance analysis of response surface experimental regression equation of optimization of the mechanical properties of OWF/PLA composites
Source Tensile strength Significance F value P value Model 102.27 <0.0001 *** A 57.83 0.0001 ** B 98.50 <0.0001 *** C 63.86 <0.0001 *** AB 135.15 <0.0001 *** AC 37.66 0.0005 ** BC 41.22 0.0004 ** A2 28.30 0.0011 ** B2 443.96 <0.0001 *** C2 0.31 0.5923 Lack of fit 3.02 0.1566 R2 0.9925 RAdj 2 0.9827 CV 0.66 Notes: F—Ratio of the mean square to the residual term; P—Influence degree value of each factor; ***—Significant in [−∞, 0.0001]; **—Significant in [0.0001, 0.01]; *—Significant in [0.01, 0.05]; R2—Coefficient of determination; RAdj 2 —Adjusted R2; CV—Coefficient of variation. 表 4 复合材料的结晶过程参数
Table 4. Crystallization process parameters of composites
Sample Tg/℃ Tcc/℃ Tm/℃ ΔHcc/
(J·g−1)ΔHm/
(J·g−1)Xc/% WF/PLA 62.9 91.6 168.1 11.97 27.98 42.7 OWF/PLA 61.7 89.9 168.0 11.82 29.88 45.6 Notes: Tm—Melting temperature; ΔHcc—Cold crystallization enthalpy; ΔHm—Melting enthalpy; Xc—Crystallinity. -
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