【作者】 修慧娟；

【导师】 韩卿；

【作者基本信息】 陕西科技大学 ， 制浆造纸工程， 2013， 博士

【摘要】 天然植物纤维是自然界中最为丰富的可再生资源，具有生物可降解性和环境友好性的特点，其主要成分纤维素、半纤维素和木素大分子结构中含有能够参与化学反应的官能团，可制备出多种用途的功能性材料，如高吸水材料、重金属离子吸附材料、医疗卫生用材料等。在诸多纤维制品中，热塑性复合材料因具有环境友好性，其制备技术是目前较为活跃的研究热点。天然植物纤维可以通过酯化、醚化等方法改变其热性能，从而制备出具有良好热塑性能的功能材料。具有热塑性的纤维可替代部分化石原料，通过热压成型的方法制成各种性能优良，并可自然降解的复合材料。这既能减少人类对化石资源的依赖，又能为天然植物纤维的高效利用找到新的途径，缓解世界能源、环境和生态问题，具有非常重要的意义。论文中以天然针叶木纤维为原料，在前人研究工作的基础上，较系统的研究了纤维氰乙基化改性、苄基化改性以及烷基化改性的工艺和改性纤维的相关性能。丙烯腈氰乙基化改性针叶木纤维的最佳工艺为：在纤维打浆度为40°SR时，经KSCN饱和的1mol/LNaOH溶液浸渍2h，丙烯腈用量为8.5mL/g（对绝干纤维），在50℃下反应2h，改性纤维增重率可达92.31%，N元素含量为12.88%，相应取代度为2.91。苄基氯苄基化改性针叶木纤维的最佳工艺为：苄基氯用量5mL/g（对绝干纤维），NaOH溶液浓度为30%，NaOH溶液用量5mL/g（对绝干纤维），反应时间5h，反应温度105℃。在此条件下改性纤维的增重率为129.47%，纤维中C元素的含量为67.30%，相应取代度为1.58。采用十六烷基三甲基溴化铵作催化剂后改性纤维的增重率提高到了149.53%，纤维中C元素的含量提高到了71.55%，相应的取代度达到了2.24。环氧氯丙烷烷基化改性针叶木纤维的最佳工艺为：环氧氯丙烷用量为5mL/g（对绝干纤维），6mol/LNaOH溶液用量为4mL/g（对绝干纤维），十六烷基三甲基溴化铵用量为0.01g，1,4-二氧六环用量为7.5ml/g（对绝干纤维），反应温度为70℃，反应时间6h。在此条件下改性纤维的环氧值为8.39mmol/g，增重率为88.67%，相应取代度为2.56。对塑化改性后的纤维采用红外光谱、X射线衍射、扫描电镜、热重和差式扫描量热分析等技术手段进行了结构和性能的分析表征。红外光谱图显示，经氰乙基化改性、苄基化改性以及烷基化改性纤维都出现了相应的特征吸收峰(氰乙基化纤维在2257cm^-1处出现了-CN吸收峰；苄基化纤维分别在3062cm^-1、3029cm^-1、736cm^-1和697cm^-1处出现了表征芳环结构的新吸收峰；烷基化纤维的谱图中1160cm^-1处则充分显示了醚键吸收峰的加强)；扫描电镜观察发现改性后纤维表面都被改性产物包覆，纤维圆挺，体积膨胀，说明改性反应已经深入到纤维细胞壁内部；X射线衍射图分析表明氰乙基化改性、苄基化改性以及烷基化改性纤维的相对结晶度都比天然针叶木纤维的要低很多，分别下降到了7.26%、23.14%和21.40%；热重和差式扫描量热曲线分析表明，三种改性方法所获得的纤维都具有了热塑性，其玻璃化转变温度分别约为85℃、134℃和137℃。从反应的难易程度以及改性纤维的热塑性两方面综合比较，氰乙基化改性能在较温和的条件下赋予改性纤维较好的热塑性，而苄基化改性温度较高，烷基化改性耗时较长，且后两者改性纤维的热塑性都不如氰乙基化纤维，所以，氰乙基化改性是针叶木纤维塑化改性较适宜的方法。通过研究反应温度、反应时间对针叶木纤维塑化改性效果的影响，分析了各反应的动力学特性，并确定了不同反应温度下针叶木纤维塑化改性反应的速率常数和表观活化能。在改性试剂用量过量的情况下，天然针叶木纤维的氰乙基化、苄基化、烷基化改性反应都属于一级反应。氰乙基化反应在40℃和50℃下的反应速率常数分别为1.04和1.62，反应表观活化能为36.58kJ/mol；苄基化反应在95℃、100℃、105℃条件下的反应速率常数分别为0.12、0.15、0.18，反应表观活化能为46.06kJ/mol；烷基化反应在60℃、70℃和80℃下的反应速率常数分别为0.11、0.25和0.35，反应表观活化能为48.14kJ/mol。课题还以针叶木木粉为原料研究分析了原料中一些少量组分对塑化改性效果的影响。研究表明：原料中的苯醇抽出物和木素等组分的含量会对其化学改性产生影响。去除苯醇抽出物后，马尾松木粉的氰乙基化改性产物增重率提高了8.27%，苄基化改性产物增重率提高了5.88%，烷基化改性产物增重率提高了7.31%；并且，原料中木素的去除打开了改性试剂渗透的通道，显著提高了马尾松木粉氰乙基化、苄基化、烷基化的反应性能，改性产物的增重率随着木素去除量的增加而增加。热重曲线说明，改性木粉的热稳定性比原马尾松木粉下降，并且随着木粉中木素去除量的增大而逐渐下降。最后，研究了植物纤维物理结构性能改变对其塑化改性的影响，并揭示了氰乙基化、苄基化和烷基化产物增重率和热性能之间的关系。结果表明，机械磨浆不会改变天然针叶木纤维的化学结构和晶型，但是却能够破坏纤维内部的氢键结合，使纤维表面分丝，结晶度下降，保水值增大，显著提高纤维素纤维对改性试剂的可及度和化学反应活性。改性纤维的增重率随着纤维磨浆程度的增加而增加。红外光谱分析显示，改性纤维的特征吸收峰强度随着纤维打浆度、改性增重率的增加而增强；改性后纤维的热重和差式扫描量热曲线显示改性纤维的热塑性随纤维增重率的提高而改善，说明机械磨浆能够有效提高天然针叶木纤维的反应性能。与未磨浆纤维相比，打浆度49°SR纤维氰乙基化改性后玻璃化转变温度从135℃降低到了83℃，苄基化改性纤维的玻璃化转变温度从162℃降低到了119℃，烷基化改性纤维的玻璃化转变温度从189℃降低到了132℃。更多还原

【Abstract】 Natural plant fibers are the most abundant renewable resources in the nature world, which are biodegradable and compatible with environment. The major components of natural plant fibers are cellulose, hemicellulose, and lignin. The functional groups of these components are employed in preparation of functional materials with versatile applications, including materials for water absorbing, heavy metal ion absorbing, medical and health, and so on. Among all the fibers, thermoplastic composites are focused currently because of their environmental compatibility. The thermal stability of natural plant fibers are decreased by esterification and etherification thus functional materials with good thermoplasticity can be obtained. Thermoplastic fibers can be made into high-performance and biodegradable composites by thermoforming in replacement of fossil based materials partially. This will reduce the dependency on fossil resources as well as find a new way to applications of natural plant fibers. Furthermore, it will have an important significance on the ease of energy, environment, and ecology issues in China.In this dissertation, natural softwood fibers were selected as resources. The fiber modification processes through cyanoethylation, benzylation, and alkylation were studied as well as the properties of the modified fibers based on previous research.The optimal process condition for softwood fibers modification by acrylonitrile cyanoethylation was given by followings:fibers were immersed in KSCN saturated1mol/L NaOH aqueous solution for2h under the beating degree of40℃SR; the dosage of acrylonitrile was8.5mL per gram of absolute dry fibers; reaction was carried out at50℃for2h. The weight gain rate of modified fibers reached92.31%, the nitrogen content was12.88%, and the corresponding degree of substitution was2.91(elemental analysis).The optimal process condition for softwood fibers modification by benzyl chloride benzylation was given by followings:the dosage of benzyl chloride was5mL per gram of absolute dry fibers; the concentration of NaOH aqueous solution was30wt.%; the dosage of NaOH aqueous solution was5mL per gram of dry fibers; the reaction was carried out at105℃for5h. The weight gain rate of modified fibers was129.47%, the carbon content was67.30%, and the corresponding degree of substitution was1.58. In presence of cetyl trimethyl ammonium bromide catalysts, the weight gain rate of modified fibers was149.53%, the carbon content was increased to71.55%, and corresponding degree of substitution reached2.24.The optimal process condition for softwood fibers modification by epoxy chloropropane alkylation was given by followings:the dosage of epichlorohydrin was5mL per gram of absolute dry fibers; the dosage of6mol/L NaOH aqueous solution was4mL per gram of absolute dry fibers; the dosage of cetyl trimethyl ammonium bromide catalyst was0.01g; the dosage of1,4-dioxane was7.5mL per gram of absolute dry fibers; the reaction was carried out at70℃for6h. The epoxy value of modified fibers was8.39mmol/g, the weight gain rate was88.67%, and the corresponding degree of substitution was2.56.Thermoplastified fibers were analyzed and characterized by IR, XRD, SEM, TGA, and DSC. The characteristic absorption peaks of cyanoethylated, benzylate, and alkylated fibers were observed from IR spectrum (-CN at2257cm-1; new absorption peaks at3062cm-1,3029cm-1,736cm-1,and697cm-1; enhanced absorption peak intensity of ether bonds of the alkylated fibers). The SEM photo exhibited that orignial fibers were coated by modified products. Modified fibers were round and erect with volume expansion. The calculations based on XRD photos showed the crystallinity was reduced to7.26%,23.14%, and21.40%. TGA and DSC analysis indicated that fibers had thermoplasticity after modification. The glass transition temperatrues of cyanoethylated, benzylated, and alkylated fibers were85℃,134℃, and137℃.Comprehensively analysing the difficulty of of plasticizing reaction and the thermoplasticity of modified fiber, it was clear that cyanoethylation modification could give modified fiber better thermoplasticity under some mild conditions. However, the temperature of benzylation was higher and alkylation was time-consuming, and the thermoplasticity of modified fiber was not in the same class as cyanoethyl fiber. So, cyanoethylation was more appropriate for plasticizing softwood fibers. The reaction kinetics of the modification process was analyzed by studying the influences of reaction temperatures and reaction times on the modification effects of softwood fibers. The rate constant and apparent activation energy at different temperatures were determined,In case of excessive modification reagents dosage, all the cyanoethylation, benzylation, and alkylation were first-order reactions. The rate constants of cyanoethylation were1.04and1.62at40℃and50℃, and the apparent activation energy was36.58kJ/mol. The rate constants of benzylation were0.12,0.15, and0.18at95℃,100℃, and105℃, and the apparent activation energy was46.06kJ/mol. The rate constants of alkylation were0.11,0.25, and0.35at60℃,70℃, and80℃, and the apparent activation energy was48.14kJ/mol.The influences of some minor components on the thermoplastification effects of Mason pine wood powders were studied. The benzyl alcohol extractives and the lignin constituents had effects on the chemical modification. After the removal of benzyl alcohol extractives, the weight gain rates of cyanoethylated, benzylated, and alkylated Mason pine wood powder were increased8.27%,5.88%, and7.31%. At the same time, the removal of lignin from raw biomass opened the diffusion tunnels of modification reagents, which reinforced the cyanoethylation, benzylation, and alkylation performance significantly. The weight gain rate of modified products increased with the amount of lignin removed from the resources. TGA curves revealed that the thermal stability of modified wood powder was lower than original Mason pine wood powder. The thermoplasticity of Mason pine wood powder were strengthened with the amount of lignin removed and weight gain rate increasing.Finally, the influences of the physical structure property changes on the effects of thermoplastification were studied. It was observed that there was relationship between the weight gain rates of cyanoethylation, benzylation, and alkylation and the properties of modified products. The results showed that the chemical structures and crystal categories were not changed by mechanical refining. However, the hydrogen bonds of fibers were destroyed, which resulted in external fibrillation, reduction of crystallinity, and increase of water retention value of the fibers. The accessibility and chemical reactivity of cellulose fibers were also enhanced consequently. The weight gain rates of modified fibers increased with the beating degree of pulp fiber increasing. IR spectrum showed that the peak intensities of modified fibers were reinforced with the increase of beating degree and weight gain rate. The TGA and DSC curves of modified fibers exhibited that refining could increase the reactivity, decease the stability, and enhance the thermoplasticity of natural softwood fibers. Compared with the fibers unrefined, the glass transition temperature of cyanoethylated fiber(beating degree49°SR) decreased from135℃to83℃, the glass transition temperature of benzylated fiber(beating degree49°SR) decreased from162℃to119℃, and the glass transition temperature of alkylated fiber(beating degree49°SR) reduced from189℃to132℃.更多还原