利用超临界CO_2技术制备γ-辐射PLLA发泡材料的研究
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摘要
聚乳酸发泡材料由于其优异的机械性能、生物可降解性和生物相容性,在生物医药、食品与医药包装等领域有良好的应用前景。鉴于生产商供应的结晶性的聚L-乳酸(PLLA)原料的熔体强度较低,造成其发泡成型过程中无法维持泡孔的稳定形态,出现大量的泡孔塌陷和合并现象；且传统工艺方法制备的PLLA发泡材料存在微观孔径较大、泡孔分布不均一和有毒有害发泡剂残留等问题。本工作将γ-辐射增黏技术和绿色环保的超临界CO2发泡技术相结合,进行了PLLA发泡材料的研究。主要内容如下：
(1)60Co-y射线辐射PLLA的增黏研究。利用聚合物熔混技术将多官能团单体三烯丙基异氰脲酸酯(TAIC)和三羟甲基丙烷三甲基丙烯酸酯(TMPTMA)分散到PLLA中,考察了γ-辐射吸收剂量对PLLA的粘均分子量(Mη)、凝胶含量和熔体流动速率(MFR)等方面的影响。结果显示：加入多官能团单体能有效的促进PLLA辐射交联,熔体强度显著提高,且TAIC的交联效果优于TMPTMA,更有利于发泡成型。多官能团单体和y-辐射吸收剂量对PLLA的结晶行为也有所影响。
(2)超临界流体C02发泡装置的研制与应用。应用常规设计方法,自主研制了超临界流体CO2实验装置,包括成型模腔、超临界流体CO2输送装置、温度测控与压力测量系统等。利用间歇成型法中的快速释压原理控制成型工艺条件,如发泡温度、饱和压力和时间等,以掌握PLLA的超临界流体C02发泡工艺条件对泡孔微观结构与性能的影响。
(3) PLLA超临界C02发泡成型工艺的研究。探究了发泡成型过程和工艺参数,并分析了PLLA发泡试样的吸水性能和降解性能。由表观密度和泡孔形态分析显示：表观密度随辐射吸收剂量增加呈先减后增的趋势,吸收剂量为10kGy时,发泡材料的表观密度最低,而与发泡温度、饱和压力与时间之间呈现不同的变化规律。随着升高的发泡温度,泡孔直径和孔隙率随之增大,而泡孔密度和表观密度减小,综合力学性能大幅度的降低；饱和压力则呈现相反的趋势,随着饱和压力的增大,泡孔更加细密均匀,相应的力学强度更加优异；随着饱和时间的增大,泡孔合并量随之增多,泡孔壁也随之变薄,造成泡孔直径增大,泡孔密度减小,拉伸强度、压缩强度及冲击强度不断降低。PLLA发泡试样的吸水率,随着吸收剂量的增加呈先增后减的趋势,吸收剂量10kGy时最大,发泡温度越高,其吸水率越大。土埋降解法发现自然环境下PLLA发泡材料的降解过程缓慢,发泡工艺条件、吸收剂量与降解率未呈现规律性的变化。
Poly(L-lactic acid) foam shows great biodegradability, biocompatibility, mechanical property and has wide application in biological medicine, food packaging. However, PLLA belongs to crystalline polymer which has poor melt strength provided by the manufacturer. Therefore, the instability during the foaming process brings about mass cell collapse and mergence as PLLA foam can't withstand the stable cell structure. The traditional foaming processes always lead to the problems such as large cellular size, uneven distribution of cells, foaming agent residues. The goal of this experiment is to prepare uniform distribution cellular poly(L-lactic acid) foam by environmentally friendly supercritical CO2foaming technology combined with simple and reliable irradiation crosslinking technology. The experiment is composed of the following three parts:
(1)Preparation and Characterization of60Co-y irradiation modification PLLA. Two different irradiation dose PLLA with different content of polyfunctional monomer TAIC and TMPTMA via60Co-y irradiation method were prepared. Viscosity-average molecular weight, melt flow rate, gel content, differential scanning calorimeter analysis indicated that polyfunctional monomer TAIC and TMPTMA enhanced the irradiation crosslinking of PLLA effectively, thus improving the melt strength. In addition, the sensitization effect of TAIC was better than that of TMPTMA, PLLA with TAIC was more conducive to foaming process. Different polyfunctional monomer and irradiation dose did influence the crystallization behavior of PLLA.
(2)Study of batch foaming apparatus via supercritical CO2. The lab apparatus for batch foaming was developed by conventional design method, including the design of moulding chamber, supercritical CO2delivery mechanism, temperature controlling monitor system, pressure measurement system, et al. To achieve the goal of studying foamig process conditions effect on the cellular microstructure, the technological parameters e.g. foaming temperature, saturation pressure, saturation time through rapid depressurization method was discussed and analyzed.
(3)Study of PLLA foaming technological parameters via supercritical CO2process. Foaming process and technological parameters such as foaming temperature, saturation pressure, saturation time together with water absorption capability and degradation performance of PLLA foam were studied and analyzed. The apparent density revealed the trend first decreased then increased with the increased irradiation dose, and reached the minimum when irradiation dose was10kGy. The apparent density showed different variation with foaming temperature, saturation pressure, saturation time. The technological parameters have great impact on the cellular microstructure of PLLA foam. The cellular size and porosity increased and cell density and apparent density decreased with the increased foaming temperature. The comprehensive mechanics performance decreased sharply. However, the saturation pressure showed the reversed trend, and the cell distribution was more uniform with fine mechanics properties. As the saturation time increasing, the cellular mergence phenomenon occupied the most and cellular wall became thinner, which cause the increased cellular size and decreased cell density with the tensile strength, compressive strength and impact strength keep decreasing. The water absorption of PLLA foam first increased then decreased with the increased irradiation dose, and the higher the foaming temperature, the greater the water absorption. The buried degradation method indicated that the degradation process of PLLA foam was rather slow under the natural environment. The technological condition and irradiation dose did't showed any regular variation with the degradation ratio.
(1)60Co-y射线辐射PLLA的增黏研究。利用聚合物熔混技术将多官能团单体三烯丙基异氰脲酸酯(TAIC)和三羟甲基丙烷三甲基丙烯酸酯(TMPTMA)分散到PLLA中,考察了γ-辐射吸收剂量对PLLA的粘均分子量(Mη)、凝胶含量和熔体流动速率(MFR)等方面的影响。结果显示：加入多官能团单体能有效的促进PLLA辐射交联,熔体强度显著提高,且TAIC的交联效果优于TMPTMA,更有利于发泡成型。多官能团单体和y-辐射吸收剂量对PLLA的结晶行为也有所影响。
(2)超临界流体C02发泡装置的研制与应用。应用常规设计方法,自主研制了超临界流体CO2实验装置,包括成型模腔、超临界流体CO2输送装置、温度测控与压力测量系统等。利用间歇成型法中的快速释压原理控制成型工艺条件,如发泡温度、饱和压力和时间等,以掌握PLLA的超临界流体C02发泡工艺条件对泡孔微观结构与性能的影响。
(3) PLLA超临界C02发泡成型工艺的研究。探究了发泡成型过程和工艺参数,并分析了PLLA发泡试样的吸水性能和降解性能。由表观密度和泡孔形态分析显示：表观密度随辐射吸收剂量增加呈先减后增的趋势,吸收剂量为10kGy时,发泡材料的表观密度最低,而与发泡温度、饱和压力与时间之间呈现不同的变化规律。随着升高的发泡温度,泡孔直径和孔隙率随之增大,而泡孔密度和表观密度减小,综合力学性能大幅度的降低；饱和压力则呈现相反的趋势,随着饱和压力的增大,泡孔更加细密均匀,相应的力学强度更加优异；随着饱和时间的增大,泡孔合并量随之增多,泡孔壁也随之变薄,造成泡孔直径增大,泡孔密度减小,拉伸强度、压缩强度及冲击强度不断降低。PLLA发泡试样的吸水率,随着吸收剂量的增加呈先增后减的趋势,吸收剂量10kGy时最大,发泡温度越高,其吸水率越大。土埋降解法发现自然环境下PLLA发泡材料的降解过程缓慢,发泡工艺条件、吸收剂量与降解率未呈现规律性的变化。
Poly(L-lactic acid) foam shows great biodegradability, biocompatibility, mechanical property and has wide application in biological medicine, food packaging. However, PLLA belongs to crystalline polymer which has poor melt strength provided by the manufacturer. Therefore, the instability during the foaming process brings about mass cell collapse and mergence as PLLA foam can't withstand the stable cell structure. The traditional foaming processes always lead to the problems such as large cellular size, uneven distribution of cells, foaming agent residues. The goal of this experiment is to prepare uniform distribution cellular poly(L-lactic acid) foam by environmentally friendly supercritical CO2foaming technology combined with simple and reliable irradiation crosslinking technology. The experiment is composed of the following three parts:
(1)Preparation and Characterization of60Co-y irradiation modification PLLA. Two different irradiation dose PLLA with different content of polyfunctional monomer TAIC and TMPTMA via60Co-y irradiation method were prepared. Viscosity-average molecular weight, melt flow rate, gel content, differential scanning calorimeter analysis indicated that polyfunctional monomer TAIC and TMPTMA enhanced the irradiation crosslinking of PLLA effectively, thus improving the melt strength. In addition, the sensitization effect of TAIC was better than that of TMPTMA, PLLA with TAIC was more conducive to foaming process. Different polyfunctional monomer and irradiation dose did influence the crystallization behavior of PLLA.
(2)Study of batch foaming apparatus via supercritical CO2. The lab apparatus for batch foaming was developed by conventional design method, including the design of moulding chamber, supercritical CO2delivery mechanism, temperature controlling monitor system, pressure measurement system, et al. To achieve the goal of studying foamig process conditions effect on the cellular microstructure, the technological parameters e.g. foaming temperature, saturation pressure, saturation time through rapid depressurization method was discussed and analyzed.
(3)Study of PLLA foaming technological parameters via supercritical CO2process. Foaming process and technological parameters such as foaming temperature, saturation pressure, saturation time together with water absorption capability and degradation performance of PLLA foam were studied and analyzed. The apparent density revealed the trend first decreased then increased with the increased irradiation dose, and reached the minimum when irradiation dose was10kGy. The apparent density showed different variation with foaming temperature, saturation pressure, saturation time. The technological parameters have great impact on the cellular microstructure of PLLA foam. The cellular size and porosity increased and cell density and apparent density decreased with the increased foaming temperature. The comprehensive mechanics performance decreased sharply. However, the saturation pressure showed the reversed trend, and the cell distribution was more uniform with fine mechanics properties. As the saturation time increasing, the cellular mergence phenomenon occupied the most and cellular wall became thinner, which cause the increased cellular size and decreased cell density with the tensile strength, compressive strength and impact strength keep decreasing. The water absorption of PLLA foam first increased then decreased with the increased irradiation dose, and the higher the foaming temperature, the greater the water absorption. The buried degradation method indicated that the degradation process of PLLA foam was rather slow under the natural environment. The technological condition and irradiation dose did't showed any regular variation with the degradation ratio.
引文
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