【作者】 李发学；

【导师】 俞建勇； 曹阿民；

【作者基本信息】 东华大学 ， 纺织材料与纺织品设计， 2006， 博士

【摘要】 随着环境污染问题的日益严重，生物可降解高分子材料越来越引起人们的重视。脂肪族聚酯由于具有良好的生物降解性已成为可降解纺织品研发的热点。聚丁二酸丁二醇酯（PBS）因具有良好的生物降解性能与可控生物降解速度而受到特别青睐。然而较低的熔点（约114℃）对由其制成纤维的纺织加工带来许多制约。芳香族聚酯虽不具备生物降解性能，但却具有优良的热力学性能、加工性能。因此，通过物理或化学的办法制成既具有脂肪族聚酯的生物降解性能又具备芳香族聚酯的物理加工性能的聚合物成为人们关注重点。在此背景下，本文通过缩聚合成方法，以对苯二甲酸二甲酯（DMT）、丁二酸二甲酯（DMS）、1，4—丁二醇（BD）为原料，以四异丙氧基钛（TTiPO）为催化剂合成了一系列高分子量的聚丁二酸丁二醇-共-对苯二甲酸丁二醇（PBST）共聚酯。通过对合成的聚合物进行核磁共振（¹H NMR）测试，证明了所合成的聚合物为PBST共聚酯。通过计算给出了PBST共聚酯中BS、BT组分的平均序列长度及无规度，表明合成的聚合物是无规共聚物。同时，核磁共振研究结果进一步表明，PBST共聚酯中BS、BT组分的实际摩尔比与合成单体投料比接近。凝胶渗透色谱仪（GPC）研究表明，PBST共聚酯的重均分子量分布在14.35～29.45万，分子量分散度大约在2.1到3.2之间。通过差示扫描量热仪（DSC），对PBST共聚酯的热学性能进行了研究。测试结果表明，随着BT摩尔分数的增加，PBST共聚酯的熔点、热焓及结晶度等均呈先降后升趋势，当BT摩尔分数为30％时，各项参数达到最小值。同时，利用Flory方程对PBST共聚酯的熔融、结晶行为与其组成关系进行了讨论，结果表明所合成的共聚酯序列结构是无规的。广角X衍射仪（WAXD）测试结果表明，随着BT摩尔分数的增加，PBST共聚酯由PBS的单斜晶型向PBT的三斜晶型转变，PBST-30为过渡点，拥有二者的混合晶型。通过聚合物的等温结晶动力学研究可知，PBST共聚酯的晶体均为球晶，晶核成核机理为均相成核。根据Hoffman-Weeks公式，计算出PBS的平衡熔点为117.9℃，PBST-10、-50和-70分别为105.9℃、173.0℃和192.5℃。利用热重分析仪（TGA）研究了PBST共聚酯以10℃／min的升温速率在氮气和空气气氛中的热降解行为。研究结果表明，PBST共聚酯在氮气气氛中的热降解过程只有一个失重阶段，而在空气中则出现两个失重阶段。利用Friedman方程计算了PBST共聚酯热降解动力学参数，结果表明所有热降解动力学参数值均与共聚酯的结构组成有关。随着共聚酯中BT摩尔分数的增加，PBST共聚酯在氮气和空气中的热稳定性均得到增强，且在氮气中热稳定性强于空气中。同时利用Friedman法、Freeman—Carroll法和Chang法分别计算出PBST共聚酯在不同升温速率下的热降解动力学参数，结果显示它们几乎都随升温速率的提高而增大，这表明试样的热降解动力学参数值受升温速率影响较大。通过比较三种方法的计算结果发现，Friedman法算出的活化能数值最小，而反应级数值则最高。利用恒温恒湿箱在60℃下，60％、70％、80％和90％的相对湿度下对PBST共聚酯进行水解实验。实验结果表明，随着水解时间的延长，PBST共聚酯的重均分子量M_w呈下降趋势；随着BT摩尔分数的增加，PBST共聚酯的M_W下降幅度先增大，而后降低，当BT摩尔分数为30mol％时，PBST共聚酯的M_W下降幅度最大。水解动力学研究发现，PBST共聚酯M_W的对数值与水解时间t呈现较好的线性关系，表明共聚酯的水解行为经历了一个自催化降解过程。通过分析水解实验条件发现，PBST共聚酯的水解速率随水解相对湿度的增加而增大，二者符合幂指函数关系；而其水解速率与水解温度并没有规律性关系。DSC测试结果表明，PBST共聚酯的熔点和热焓均随水解时间的延长而呈上升趋势。通过核磁共振研究发现，水解34天后PBST共聚酯中共聚单元的组成比例几乎没有发生变化，表明在水解过程中水分子对PBST共聚酯是无组成选择性的随机链切断。利用脂肪酶PS^?对PBST共聚酯进行酶解实验，并对酶解前后共聚酯的各项性能进行对比研究。研究结果表明，随着BT摩尔分数的增加，PBST共聚酯的失重率逐渐减小，表明共聚酯的酶解速度降低。DSC测试结果表明，PBST共聚酯的熔点和热焓随降解时间的延续均呈上升趋势，反映出聚合物的降解优先发生在无定型区或聚合物大分子链发生重结晶，小角X射线散射（SAXS）研究结果证明了这一结论。根据全反射红外（ATR-FTIR）光谱，定量计算了PBST-30共聚酯降解50天后自表面2.76μm处的深度范围内有酶解反应的发生。¹H NMR研究发现，降解前后BT结构单元在PBST共聚酯中的含量没有发生显著变化，表明脂肪酶PS^?对PBST共聚酯的降解是无组成选择性降解。通过扫描电镜（SEM）可清楚看出，降解后PBST共聚酯表面较降解前粗糙，且出现孔洞，这正是脂肪酶对共聚酯发生催化降解的结果。为了研究PBST共聚酯的可纺性，利用5升反应釜合成了不同分子量的PBST-70共聚酯，并采用毛细管流变仪对树脂进行流变性能测试。测试结果表明，PBST-70共聚酯的表观粘度随剪切速率的增加而降低，是典型的切力变稀型非牛顿流体；随着熔体温度的上升，表观粘度对剪切速率的依赖性下降。PBST-70熔体的流动活化能随剪切速率的上升而降低，故其温度敏感性也随着剪切速率的上升而下降。当剪切速率相同时，PBST-70熔体的非牛顿指数，2与温度之间近似呈线性关系，随着温度的提高，n线性增大，熔体的非牛顿性减弱；当温度不变时，随着剪切的速率的增大，熔体的n单调减小，非牛顿性增强。随着温度的提高，PBST-70熔体的结构粘度指数Δη减小，但热降解增加，所以适当的纺丝温度对于熔体的可纺性和稳定性非常重要。在相同的剪切速率下，分子量越大，PBST-70熔体的剪切应力σ，表观粘度η_a和Δη增大，n减小。更多还原

【Abstract】 As a response to the problem of increasing domestic waste, biodegradable polymers have attracted more and more attention. To date, aliphatic polyesters have been found to be the most attractive biodegradable synthetic polymers and have been applied to textiles because of good biodegradability. Poly（butylene succinate） （PBS）, one of the most important aliphatic polyesters, have already been available on the market because of good biodegradability. However, low melting point （114℃） restricts its large-scale application. On the contrary, in spit of non-biodegradability, aromatic polyesters have been known to possess excellent thermal and mechanical performances. Therefore, introducing aromatic unit into the main chains of aliphatic polyesters seems an interesting strategy to produce new aliphatic-aromatic copolyesters, sharing the favorable biodegradability of aliphatic polyester component and the good physical performance of more rigid aromatic counterpart.In the above cases, firstly, a series of aliphatic-aromatic poly（butylene succinate-co-butylene terephthalate） （PBST） copolyesters was efficiently synthesized from the starting materials of dimethyl succinate （DMS）, dimethyl terephthalate （DMT） and 1,4-butanediol （1,4-BD） in the presence of tetraisopropoxide titanium （TTiPO） as the bulk poly condensation catalyst. ¹H NMR proved the prepared products of the PBST copolyesters, and the molar ratios of BS to BT comonomers were almost equal to the feeding ratios of DMS to DMT. According to the sequential distribution, it was indicated that the synthesized polymers were randomness. GPC results showed that the weight average molecular weights （M_w） of the PBST copoyesters were in range of 14.35×10⁴-29.45×10⁴, and degree of distribution ranged from 2.1 to 3.2.From DSC investigation, it was found that melting point, fusion enthalpy and degree of crystallinity all increased with the increasing of BT comonomers, then shifted to decrease. When BT molar fraction was 30%, the lowest thermal parameters were obtained. Furthermore, the relations between thermal properties and copolyester components were discussed by Flory equation, which indicated the synthesized polymers were also randomness. WAXD patterns clearly revealed that the transition of crystal lattice structure from monoclinic lattice of PBS crystal to triclinic lattice of PBT crystal with an increase of BT comonomers, and when the BT comonomers content approached 30 mol%, the shift of crystal diffraction patterns from the PBS to PBT began to occur. According to isothermal crystallization kinetics, it could be known that the crystallization behaviors of PBST copolyesters were attributed to the homogeneous nucleation and spherulitic growth. In addition, the equilibrium melting points of PBS and PBST-10, -50, -70 calculated by Hoffman-Week equation were calculated for 117.9℃, 105.9℃, 173.0℃and 192.5℃, respectively.Thermal degradation behavior for the PBST copolyesters were investigated by the thermogravimetry analyzer （TGA） at a scanning rate of 10℃/min both in nitrogen and air. TGA traces showed that all the samples obviously exhibited only one weight-loss stage when they were heated up to high temperature in nitrogen, while two weight-loss stages were found under the atmosphere of air. According to the Friedman model, the kinetic parameters exhibited the dependence on the BT comonomers composition. Thermal stability was enhanced generally with increasing the content of BT comonomers in both nitrogen and air, and was much better in nitrogen than in air. Moreover, the results obtained by the three models indicated most of the kinetic parameters tended to increase significantly with the thermal scanning rate, implying a strong thermal scanning rate dependence of degradation kinetic parameters. Among the three models, the Friedman model presented the lowest activation energy value but the highest thermal degradation reaction order value.The enzymatic degradation was carried out in the presence of a lipase originated from Pseudomonas cepacia (Lipase PS^?). The weight-loss of PBST was found to decrease with increasing BT content, indicative of decreasing enzymatic degradation rate. DSC curves showed the melting points and fusion enthalpies increased with prolonging the degradation time, which implied that amorphous regions were hydrolyzed prior to crystalline regions or macromolecular chains resulted into recrystallization. The results were confirmed by SAXS analysis. From ATR-FTIR, the degradation depth from the surface of PBST-30 was calculated quantitatively for 2.76μm after 50 days. ¹H NMR analysis showed the BT content kept unchanged after degradation, suggesting the Lipase decomposed the PBST copolyesters unselectively. Besides, it could be clearly observed that the surface of the PBST copolyesters became coarser after degradation than original samples, and many holes appeared in SEM photos.The hydrolysis behavior of PBST was conducted at 60℃under predetermined relative humidity of 60, 70 and 90%RH in an IG-400 humidic chamber. According to the results, it could be observed that the reducing extent of M_w of PBST first increased, then slowly decreased when BT molar fraction was more than 30%. The studies on hydrolysis kinetics revealed the logarithmic plots of M_w as a function of hydrolysis time t exhibited good linearity, which suggested the domination hydrolysis mechanism for the PBST copolyesters was autocatalytic random hydrolysis process. By investigating the effects of test conditions on hydrolysis behavior, it could be found that the hydrolysis rate increased with the increase of relative humidity, but was independent of hydrolysis temperature. Furthermore, ¹H NMR analysis for the PBST copolyesters after hydrolysis revealed little change in composition within experimental limits, indicating the hydrolysis behavior had no choice between BS and BT comonomers.In order to study the spinnability of the PBST copolyesters, PBST-70 with different molecular weights prepared by 5 litres synthesis kettle were selected to investigate their rheological behavior by capillary rheometer. The results showed that the apparent viscosity of PBST-70 decreased with the increase of shear rate and temperature. The shear-thinning results indicated the melt solution belonged to non-Newtonian pseudoplastic fluid. The flow activation energy of PBST-70 decreased with increasing shear rate, so the sensitivity to temperature decreased accordingly. When shear rate kept unchanged, the good linearity could be obtained by plotting non-Newtonian index n of PBST-70 fluid to temperature. Higher the temperature was, larger n became. When temperature stayed steady, n decreased with the increase of shear rate. With the increase of temperature, structural viscosity index of PBST-70 tended to decrease, however, the possibility of thermal decomposition increased. Therefore, it was important to select suitable spinning temperature for the spinnability and stability. In the same shear rate, higher the molecular weight of PBST-70 was, larger the shear stress, apparent viscosity and structural viscosity index were, but smaller n became.更多还原