【作者】 汪振炯；

【导师】 顾正彪；

【作者基本信息】 江南大学 ， 粮食、油脂与植物蛋白工程， 2012， 博士

【摘要】 利用廉价生物质可再生资源开发绿色高性能环境友好型木材胶粘剂是人类不懈追求的目标。而现有以淀粉为主要原料的淀粉基木材胶粘剂的制备工艺普遍存在淀粉用量低、稳定性差、保质期短、工艺复杂等问题,限制了其相关产业的发展。针对这一问题,本论文瞄准产业需求,结合统计分析、结构表征等手段,对淀粉基环境友好型木材胶(以下简称淀粉木材胶)制备的基础工艺进行系统研究,探索出高淀粉用量下淀粉木材胶的制备工艺;在此基础上,对淀粉木材胶制备工艺中各影响因素的相关机理进行了解析,并进行了相应的工艺参数的优化和建模工作;此外,论文研究了助剂的添加对淀粉木材胶关键性能的影响,并初步探索了相关机理;在小试基础上,最终实现了中试放大,获得了一种高淀粉用量的常温使用型淀粉基环境友好型木材胶粘剂,其淀粉用量可达胶粘剂总不挥发物含量的43.9%;并且产品的各项指标达到相关胶粘剂的行业标准。为探析淀粉木材胶制备的基础工艺,本文首先采用物理共混和接枝共聚方法制备高淀粉含量的淀粉木材胶,结果证明物理共混会导致相分离现象出现,造成胶粘剂粘接性能及稳定性均较差;而接枝共聚可以增强胶粘剂分子结构,有利于出制备高淀粉含量的淀粉木材胶。因此确定接枝共聚作为制备淀粉木材胶的核心工艺。确定工艺后,本文随即研究了不同手段(糊化预处理、乳化剂)对淀粉木材胶前期接枝共聚工艺的影响及相关机理,并在此基础上利用响应面法对淀粉木材胶制备工艺进行了相关优化,建立了数学模型。相关研究内容如下:1.从前处理的角度研究了糊化预处理对淀粉木材胶的胶接强度和低温储藏稳定性的影响。对比没有经过糊化预处理的淀粉木材胶,经过糊化预处理的淀粉木材胶的干强度提高了20.9%,湿强度提高了45.8%,同时糊化预处理可以显著提高反应的接枝参数。耐低温稳定性实验证明糊化预处理可以增加淀粉木材胶通过低温储藏-室温解冻循环(以下简称冻融循环)的次数。动态时间扫描实验和XRD实验的结果证明了糊化预处理有利于削弱淀粉分子之间的氢键作用力,促进淀粉与单体之间发生接枝反应,从而改善了淀粉木材胶的粘接性能及结构稳定性。2.从促进接枝共聚反应的角度研究了乳化剂对淀粉木材胶胶接强度和低温储藏稳定性的影响。结果证明,阴离子乳化剂十二烷基硫酸钠(SDS)可以有效提高淀粉木材胶的粘接性能和耐低温储藏性能。SDS的最佳添加量为淀粉用量的1%(w/w),在此添加量下,淀粉木材胶干强度可达4.75MPa,而湿强度达到1.81MPa。此外还发现SDS可以有效的提高反应的接枝参数,如接枝率提高了80.9%,而接枝百分率提高了45.1%。动态时间扫描实验结果证明SDS提高淀粉木材胶性能的机理在于乳化剂消弱了淀粉分子之间的氢键作用力,有利于淀粉和单体之间的接枝反应,低场核磁和TEM的结果证明SDS可在淀粉表面形成保护层有助于保水作用,防止乳液粒子聚集,有利于提高乳液的稳定性。3.在上述研究基础上,运用响应面法(RSM)对淀粉木材胶的工艺参数进行统计分析及优化,研究了酸解时间、初始过硫酸铵(APS)用量、乳化剂SDS用量、引发pH值等四个主要影响因素分别对粘度和干强度的影响。结果表明此四个因素对干强度和粘度均存在明显的相关性,响应面优化得到的最佳工艺为酸解时间37.5min;APS用量为淀粉用量的0.94%(w/w),其中初始用量为淀粉用量的0.74%(w/w);乳化剂用量为0.82%(w/w);引发pH为5.85。获得较好的接枝共聚工艺之后。本文对能进一步提高淀粉木材胶性能的助剂进行了研究,主要考察了提高淀粉木材胶的储藏性能和耐水性能的相关助剂,相关研究内容如下:1.在提高淀粉木材胶耐储存性方面,研究了尿素对淀粉木材胶流变学特性和耐低温储藏性能以及粘接性能的影响。实验结果表明尿素的添加对粘接性能影响较小。此外,尿素的添加有效降低了淀粉木材胶的粘度及体系的假塑性,同时显著提高了淀粉木材胶通过冻融循环的次数,最佳添加量是加入干重为占淀粉用量为15%(w/w)的尿素;动态时间扫频实验和低场核磁实验的结果证明尿素提高淀粉木材胶耐冻融循环能力的机理可以归结为尿素削弱了淀粉木材胶分子之间的氢键作用,抑制了体系向弱凝胶体系发展,从而提高了淀粉木材胶的耐低温储藏能力。2.在提高淀粉木材胶耐水性方面,研究了纳米二氧化硅粒子(以下简称纳米硅粒子)对淀粉木材胶性能的影响。添加纳米硅粒子的淀粉木材胶后干强度和湿强度显著提高。与未添加的空白对照相比,添加干重占淀粉用量10%(w/w)的纳米二氧化硅溶胶的淀粉木材胶的干剪切强度从5.92MPa增加到8.36MPa,而湿剪切强度从2.11MPa增加到3.47MPa。利用红外热重流变等手段研究了纳米硅粒子提高淀粉木材胶性能的机理,结果证明,纳米硅粒子可以和淀粉胶分子作用形成氢键,增强了胶粘剂分子的结构,从而提高了淀粉木材胶的粘接能力。经一系列工艺改良后,论文最终实现了中试放大,实现了高淀粉用量下淀粉木材胶的稳定制备,其淀粉用量可达胶粘剂总不挥发物含量的43.9%左右。中试产品的各项指标并达到相关胶粘剂的行业标准。经济性分析表明淀粉木材胶具有较低的成本,其原料成本大约为商品白乳胶的70%左右。综上所述,本课题所制备的淀粉基环境友好型木材胶粘剂在具有优良性能的同时,还具有较低的成本,因此在木材工业中具有较好的推广价值和市场前景。更多还原

【Abstract】 To develop high performance wood adhesive by utilizing low cost biomass is unremitting pursuit goal. In our paper, a new, environmentally friendly starch-based wood adhesive high starch content was synthesized via graft polymerization of vinyl acetate monomer onto waxy corn starch, and the effects of raw materials, emulsifiers, diluents urea, nano-additives was investigated and the technological parameter of starch-based was also optimized accordingly.Firstly, the basic process of starch-based wood adhesive was studied. Physical blending and grafted copolymerization was used to prepared to starch-based wood adhesive with high starch content. The result showed that the starch-based adhesive prepared by the physical blend had poor bonding performance and poor stability for the physical phase separation. While the starch-based wood adhesive prepared by graft copolymerization had better performance than the starch-based adhesive prepared by the physical blend.Secondly, based on the basic Process, the effects of gelatinization pretreatment of starch on storage stability at low temperature and bond strength of starch-based wood adhesive were investigated. Compared with starch-based wood adhesive without gelatinization pretreatment of starch, the bonding strength of starch-based wood adhesive increased after gelatinization pretreatment, the increasement were 20.9% in dry-state and 45.8% in wet-state, respectively. The grafted parameters was also remarkably increased by the gelatinization pretreatment of starch, such as G increased by 43.5% and GE increased by 38.8%. Result of freeze-thaw stability measurement indicated that the gelatinization pretreatment of starch could effectively improve the frost resistance of starch-based wood adhesive. The results of dynamic time sweep experiments and XRD analysis demonstrated that the gelatinization pretreatment of starch could weaken intermolecular hydrogen bonds of starch, and enhance the grafted reaction of starch and VAc monomer, thereby improving the bonding properties and stability of starch-based wood adhesive emulsion.In addition, the effects of emulsifiers （SDS） on storage stability in low temperature and bond strength of starch-based wood adhesive were also investigated. Compared to starch-based wood adhesive without emulsifiers, emulsifier-fortified starch-based wood adhesive all exhibited enhanced glue strength. The optimum amount of SDS is 1% of starch content. In particularly, SDS has a most significant effect that dry strength of starch-based wood adhesive was increased to 4.75MPa and the wet strength was increased to 1.81MPa, respectively. The grafted parameters was also remarkably increased by the added of SDS, such as G increased by 80.9% and GE increased by 45.1%. The results of dynamic time sweep experiments and TEM and Low field Nuclear magnetic resonance technique （LF-NMR） showed that SDS could weaken the hydrogen bonding force of the starch molecules, and significantly enhanced the parameters of grafted reaction, thereby finally improving the bonding properties and stability of starch-based wood adhesive emulsion.In order to maximize the performance of starch-based wood adhesive, response surface methodology （RSM） was employed to optimize the grafted reaction condition. The RSM model showed that the shear strength and viscosity were related to acidolysis time （X₁）, initiate APS dosage （X₂）, emulsifier dosage（X₃） and initiate pH（X₄）. The optimum extraction conditions were acidolysis time of 37.5min, initiate APS dosage of 0.74% of starch content （the total APS of 0.94% of starch content）, emulsifier dosage of 0.84% of starch content and initiate pH of 5.85.Thirdly, in order to enhance the performance of starch-based wood adhesive, the additives which can further improve the performance of adhesive were also studied.To improve the frost resistance of starch-based wood adhesive in low temperture, the effects of urea on the performance of starch-based wood adhesive were evaluated, including freeze-thaw stability, rheological properties and bond behavior. The results indicated that starch-based wood adhesive with added urea still showed characteristics of non-Newtonian fluid. With the amount of urea increased, the non-Newtonian index would increase and the structural viscosity index would decrease. Result of freeze-thaw stability measurement indicated that added 15%（w/w）urea solution could effectively improve the frost resistance of starch-based wood adhesive. Results of dynamic time sweep experiments and LF-NMR indicated that the addition of urea could inhibit the formation of weak gel in the starch-based wood adhesive system and enhance structural stability of starch-based wood adhesive, whether the room temperature or freezing and thawing conditions. In addition, result of bond behavior indicated that urea had little influence on the bonding strength of starch-based wood adhesive. Therefore, urea can be used as an effective additive for improving storage performance starch-based wood adhesive.Furthermore, slica nanoparticles were used to improve the water resistance of starch-based wood adhesive in this study. Compared with starch-based wood adhesive without silica nanoparticles, the bonding strength of starch-based wood adhesive with 10%（w/w）of silica nanoparticles increased to 8.36MPa in dry state and 3.47MPa in wet state. The improved performance of SiO₂/starch-based wood adhesive was supported by its strengthened molecular structure, enhanced thermal stability and beneficial changes in rheological properties from the analysis results using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analyzer and rheometer.Finally, after a series of process optimization, the starch-based wood adhesive high starch content was successfully synthesized in factory, and the performance of the starch-based wood adhesive could reach the national standards of PVAc wood adhesive. The content of starch is about the 43.9% of the solid content of the starch-based wood adhesive. The economical analysis showed that the starch-wood adhesive has a lower cost, and its raw material cost is about 70% of PVAc emulsion wood adhesive. In summary, the starch-based wood adhesive is a kind of environment-friendly wood adhesives with lower cost and high performance and it will be a good extended value and market prospect in wood industy.更多还原