摘要
研究了壳聚糖和聚乙烯醇在改善纸基材料水蒸气(极性气体)和氧气(非极性气体)阻隔性能上的应用效果,探讨了壳聚糖/聚乙烯醇不同质量比和不同复合方式(共混和分层)对纸基材料水蒸气和氧气阻隔性能、机械性能和涂层稳定性的影响。结果表明,随着壳聚糖和聚乙烯醇质量比的降低,纸基材料的水蒸气阻隔性能逐渐增强,同时氧气阻隔性能逐渐降低;壳聚糖/聚乙烯醇分层涂布纸的水蒸气和氧气透过量均低于壳聚糖/聚乙烯醇共混涂布纸。当壳聚糖和聚乙烯醇的质量比为1∶1时,壳聚糖/聚乙烯醇分层涂布纸的水蒸气透过量和氧气透过量分别为9.36 g/(
纸基材料由于成本低、可生物降解、可回收、机械强度高和质量轻等优点,在全生命周期评估(Life Cycle Assessment,LCA)中被认为是最具应用前景的绿色可持续包装材料,已广泛应用于包装行
壳聚糖是甲壳素去乙酰化的衍生物,由2-氨基-2-脱氧-β-D-葡聚糖通过(1-4)糖苷键连接而成,可溶于酸性水溶液中(氨基在pH值<6.2的介质中发生质子化反应),是目前唯一的天然阳离子多
目前文献中对壳聚糖膜和聚乙烯醇膜材料均已有大量研
壳聚糖(CS,脱乙酰度86.1%,黏度87 mPa·s,浙江金壳药业股份有限公司);聚乙烯醇(PVA,型号T66,醇解度98%~99%,黏度11.6~15.4 mPa·s,分子质量400);冰乙酸(分析纯),天津市河东区红岩试剂厂;丙三醇(分析纯),国药集团化学试剂(北京)有限公司;基纸(普通A4复印纸,定量70 g/
Mayer棒涂布器,RDS,美国;低温高湿试验箱,SDJ001F,重庆英博;纸与纸板厚度测定仪,PN-PT6,杭州品享科技有限公司;水蒸气透过率测定仪,W3/062,济南兰光机电技术有限公司;氧气透过率测定仪,Y110,广州标际包装设备有限公司;电脑测控抗张试验机,DCP-KZ1000,四川长江造纸仪器有限责任公司;Cobb吸水性测定仪,P95933,PTI公司;扫描电子显微镜(SEM),S-3400N,日立先端科技股份有限公司;傅里叶变换红外光谱仪(FT-IR),TENSOR27,德国布鲁克;热重分析仪,TGA/DSC I,瑞士Mettler Toledo。
CS涂布液制备:将CS粉末加入水中,并加入一定量的乙酸和甘油,以600 r/min速度搅拌4 h,配制质量分数1%、1.5%、2%、3%的CS溶液,控制CS/乙酸/甘油质量比为1∶0.5∶0.2,静置消泡,备用。
PVA涂布液制备:将PVA粉末加入水中,在90℃水浴中,以600 r/min速度搅拌4 h,配制质量分数10%的PVA溶液,冷却至室温备用。
CS/PVA涂布液制备:将制备好的CS溶液与PVA溶液按CS与PVA质量比分别为1∶0、1∶0.5、1∶1、0.5∶1、0∶1混合,以600 r/min速度搅拌2 h,得到CS/PVA涂布液。


图1 纸基材料的水蒸气和氧气透过量及不同涂布方式示意图
Fig. 1 Water vapor and oxygen transmission rate of paper-based materials and schematic diagram of different coating methods


图2 CS/PVA复合涂布方式和CS/PVA质量比对纸基材料水蒸气阻隔性能的影响
Fig. 2 Effects of coating methods and CS/PVA mass ratio of CS/PVA composite on water vapor barrier properties of paper-based materials
由
(1) |

图3 CS/PVA复合涂布方式和CS/PVA质量比对纸基材料氧气透过量的影响
Fig. 3 Effect of coating method of CS/PVA composite and CS/PVA mass ratio on oxygen transmission rate of paper-based materials

图4 CS、PVA和CS/PVA复合材料的红外光谱图
Fig. 4 FT-IR spectra of CS, PVA and CS/PVA composites
TG用于评估以温度为函数的CS、PVA和CS/PVA(质量比1∶1)的质量变化。DTG是TG曲线的一阶导数。本研究中将3种涂层单独成膜,并进行热稳定性分析,结果如


图5 CS、PVA和CS/PVA复合涂层的TG与DTG曲线
Fig. 5 TG and DTG curves of CS, PVA and CS/PVA composite
通过扫描电子显微镜(SEM)观察纸基材料涂层的表面和截面形貌,如

图6 纸基材料SEM图
Fig. 6 SEM images of paper-based materials
本研究通过Cobb值来表征纸基材料的耐水性,进一步说明不同复合方式之间的差异。以UPM A4复印纸为基纸,其具有较低的Cobb值(27.93 g/

图7 不同质量比CS/PVA涂布纸基材料的Cobb值
Fig. 7 Cobb values of CS/PVA coated paper-based materials with different mass ratio
食品包装不仅需要良好的氧气和水蒸气阻隔性能,还应具有良好的机械性能,一般通过抗张性能来表征。

图8 不同质量比CS/PVA涂布纸基材料的抗张性能
Fig. 8 Tensile index of CS/PVA coated paper-based materials with different mass ratio
CS薄膜具有良好的抗张强度和断裂伸长
本研究将壳聚糖(CS)和聚乙烯醇(PVA)以不同的复合方式(共混和分层)和不同质量比涂布于基纸表面,探讨二者在改善纸基包装材料气体阻隔能力方面的差异。
3.1 将PVA引入CS涂层中来提高纸基材料的气体阻隔性能,控制总涂布量4.5 g/
3.2 通过对比分析发现,CS与PVA不同复合方式对纸基材料的气体阻隔性能有较大影响。CS/PVA分层涂布的纸基材料的氧气阻隔、水蒸气阻隔和Cobb值均好于共混涂布的纸基材料,而抗张强度相差不大。当CS/PVA质量比为1∶1时,分层涂布的纸基材料的水蒸气透过量比共混涂布的纸基材料低约68%,氧气透过量降低约67%。
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