摘要
通过Pickering乳液法一步实现亲水性纤维素纳米晶体(CNC)和疏水性聚苯乙烯(PS)的高效复合,经溶液浇筑成膜与热压耦合制得力学性能优异的CNC/PS复合薄膜。结果表明,尽管CNC的添加会降低PS薄膜的透明度,但当CNC添加量≤10%时,CNC/PS复合薄膜仍能保持良好的透明度。当CNC添加量为8%时,CNC/PS复合乳液中的乳滴尺寸和乳滴分布均一性最佳,此时CNC/PS复合薄膜的力学性能最佳,其拉伸强度为33.8 MPa,远优于纯PS薄膜(18.9 MPa),韧性和杨氏模量分别为408.1 kJ/
聚苯乙烯(PS)是由苯乙烯单体聚合而成的一种重要的热塑性树
纳米纤维素是由纤维素经过化学、物理、生物或上述方法结合的手段处理,得到的至少一个维度尺寸小于100 nm的纤维聚集
贺莹莹等
PS,颗粒状,注塑级,购自山东优索化工科技有限公司; CNC,粉末状,长度50~200 nm、直径5~20 nm,购自湖州闪思新材料科技有限公司;二氯甲烷(DCM),分析纯,购自国药集团化学试剂有限公司;去离子水(电导率为2~10 μS/cm),实验室自制。
当CNC添加量(占CNC和PS总质量的比例)分别为0、2%、5%、8%、10%、20%时,采取相同步骤制备6种CNC/PS复合薄膜,依次记为纯PS、2% CNC/PS、5% CNC/PS、8% CNC/PS、10% CNC/PS、20% CNC/PS。
以8% CNC/PS 的制备步骤为例:取0.46 g PS充分溶解于10 mL的DCM,得到均一的PS/DCM溶液,然后取0.04 g CNC制备质量分数0.2%的CNC水相分散液,再将二者共混并用超声波破碎仪(Biosafer150-96,赛飞有限公司)超声处理(120 W,5 min),获得稳定的CNC/PS复合乳液。随后将CNC/PS乳液浇注至聚四氟乙烯板,先干燥(40 ℃,3 h)去除DCM,再干燥(60 ℃,12 h)获得CNC/PS复合薄膜,最后经平板硫化机(东菀市宝鼎精密仪器有限公司)热压处理(10 MPa,130 ℃,5 min),得到光滑、平整和透明度良好的CNC/PS复合薄膜,制备流程如

图1 CNC/PS复合薄膜的制备流程以及乳液的稳定性
Fig. 1 Schematic preparation process of CNC/PS composite film and the stability of CNC/PS emulsion
使用傅里叶变换红外光谱仪(FT-IR,VERTEX 80V, 德国Bruker公司)测定PS、CNC与CNC/PS复合薄膜的衰减全反射红外光谱(ATR)。扫描范围500~4000 c
使用光学显微镜(Axiolab 5,德国ZEISS公司)对CNC/PS复合乳液的形貌进行观察。
使用紫外可见近红外分光光度计(Lambda 950,美国PE公司)对CNC/PS复合薄膜进行透光率测试,波长为300~800 nm,以空气作为参照样。
使用载荷为500 N台式电子万能试验机(AG-X plus,日本岛津公司)测试CNC/PS复合薄膜的力学性能,样品尺寸为3 mm×15 mm,厚度为0.01~0.02 mm,拉伸速率为2 mm/min。每组样品平行测定7次,取平均值。
使用热重分析仪(TG,TG 209 F1,德国NETZSCH公司)对样品进行热稳定性分析。以10 ℃/min的速率将样品从室温加热到120 ℃,在该温度下保持20 min,然后以20 ℃/min速率加热到600 ℃。
使用示差扫描量热分析仪(DSC,DSC 404 F1, 德国NETZSCH公司)进行分析,氮气环境,α-Al2O3为参比,升温速率为20 ℃/min,测试CNC/PS复合薄膜的玻璃化转变温度。
采用扫描电子显微镜(SEM,Regulus 8100,Hitachi)对复合薄膜断面和热压前后的表面进行分析。液氮条件下脆断CNC/PS复合薄膜,并对复合薄膜断面处进行喷金处理,加载电压为4 kV,调整SEM的倍数观察样品。
对PS、CNC及CNC/PS复合薄膜进行红外光谱图分析,结果如

图2 CNC、PS、CNC/PS复合薄膜的FT-IR谱图和CNC/PS复合薄膜热压前后的SEM图
Fig. 2 FT-IR spectra of CNC, PS, and CNC/PS composite film, and SEM images of CNC/PS composite film before and after hot-pressing

图3 CNC/PS复合薄膜的光学性能
Fig. 3 Optical performance of CNC/PS composite films
对CNC/PS复合薄膜的力学性能进行表征,其应力-应变曲线、拉伸强度、韧性和杨氏模量如

图4 CNC/PS复合薄膜的力学性能
Fig. 4 Tensile properties of CNC/PS composite films
为了进一步探究CNC添加量对CNC/PS复合薄膜力学性能的影响机理,采用光学显微镜表征CNC/PS复合乳液形貌,结果如

图5 CNC/PS复合乳液的形貌图
Fig. 5 Morphology of CNC/PS emulsion

图6 CNC/PS复合薄膜断面的SEM图
Fig. 6 SEM images of the fracture of CNC/PS composite films
最大热分解温度(Td)与玻璃化转变温度(Tg)是决定聚合物材料应用的重要性能参数。

图7 CNC/PS复合薄膜的热稳定性分析
Fig. 7 Thermal stability of CNC/PS composite films
本研究通过Pickering乳液法一步实现亲水性纤维素纳米晶体(CNC)和疏水性聚苯乙烯(PS)的高效复合,结合溶液浇筑成膜与热压工艺制备得到力学性能优异的CNC/PS复合薄膜,对所得不同CNC添加量的复合薄膜进行分析表征。
3.1 亲水性CNC与疏水性PS的复合虽然会导致CNC/PS复合薄膜透光率的下降,但当CNC添加量≤10%时,CNC/PS复合薄膜仍能保持良好的透明度。
3.2 CNC/PS复合乳液中乳滴尺寸均一性和CNC的添加量密切相关,当CNC添加量为8%时,CNC/PS复合乳液中的液滴尺寸和液滴分布均一性最佳,并且此时CNC/PS复合薄膜的力学性能最佳,拉伸强度为33.8 MPa,远优于纯PS薄膜(18.9 MPa),韧性和杨氏模量分别为408.1 kJ/
3.3 当CNC添加量增至20%时,CNC/PS复合薄膜中明显出现了CNC的团聚现象,并且透明度也较低。但其仍具有与纯PS薄膜相当的力学性能(拉伸强度为20.9 MPa,杨氏模量为1.6 GPa),充分表明了Pickering乳液法的优越性。
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