【作者】 孙莉；

【导师】 林炜；

【作者基本信息】 四川大学 ， 生物质化学与工程， 2022， 硕士

【摘要】 制革废弃牛毛是一种来源丰富且价格低廉的角蛋白资源。目前大部分废弃牛毛并未得到充分利用,多被焚烧或填埋处理,不仅造成了资源浪费,还会带来环境污染。在双碳目标的时代大背景下,如何资源化利用废弃牛毛是制革业研究者关注的重要课题。牛毛角蛋白含有植物生长必需的氮,磷,硫及多种微量元素,将其应用于肥料领域是一种经济合理的资源化利用方式。近年来出现的水凝胶缓释肥料因具有保水能力且可明显提高养分的利用效率而备受关注。因此利用废弃牛毛开发水凝胶作为缓释肥料,符合循环经济的理念。本论文通过氧化-还原法从废弃牛毛中提取得到角蛋白水解物,利用甲基丙烯酸酐交联角蛋白水解物得到水凝胶,并研究了甲基丙烯酸酐与角蛋白水解物的化学交联机理;在此基础上,将含氮磷钾的线性聚合物半互穿负载于水凝胶中,探究了其作为缓释肥料的应用性能。主要研究内容及结果如下:1.通过氧化-还原法从制革废弃牛毛中提取角蛋白水解物（K-SH）,研究了H₂O₂处理时间对K-SH的水解率、相对分子量及活性巯基的影响。结果显示,随着处理时间的增加,牛毛在后续还原溶液中的水解率提高,但提取的K-SH的相对分子质量和其结构上活性巯基的含量降低。选择水解率为95%,相对分子量Mn为18160 g/mol的K-SH（巯基含量为61.55 umol/g）为原料,利用甲基丙烯酸酐（MA）交联K-SH成功制备新型角蛋白基水凝胶（KMA-Gel）,并研究了不同配比KMA-Gel的形貌特征、粘弹性能、机械性能、溶胀性能及生物降解性。SEM研究表明KMA-Gel形貌呈蜂窝状,属于多孔性材料。流变仪实验研究表明适当增加MA的用量有助于提高KMA-Gel网络体系的交联度。压缩实验研究表明KMA-Gel的压缩强度约为5.7 kPa,在5次循环压缩后仍然保持其结构的完整。溶胀实验表明KMA-Gel能够吸收其自身重量约四倍的去离子水。降解实验研究表明KMA-Gel具备良好的生物降解性能。当m（K-SH）:m（MA）=3:2时,所制备的KMA-Gel综合性能较好。2.本论文将MA用于交联角蛋白水解物制备得到KMA-Gel,其交联机理并不清楚,因此本章节着重研究了其成胶机理。首先通过建立小分子模型以确定K-SH结构上可能与MA发生化学交联反应。角蛋白分子结构中含有胱氨酸和半胱氨酸,将二者作为小分子模型化合物分别与MA反应制备一系列样品,借助FT-IR和¹H-NMR对其结构进行表征。结果可推测,半胱氨酸（L-Cys）中的氨基可与MA发生酰化反应从而引入了C=C双键,并同时生成甲基丙烯酸（MAA）;其中MAA先与体系中的巯基发生巯基-烯反应,而后L-Cys结构中的C=C双键再与体系中的巯基发生巯基-烯反应。紧接着改变K-SH和MA的配比制备得到可溶性改性角蛋白（KMA）,测定了KMA结构中氨基及巯基转化度,并通过FT-IR、¹H-NMR和XPS对比分析了KMA的结构变化。结合上述小分子模型实验结果,推测得到KMA-Gel的化学交联机理为:K-SH结构中的氨基可与MA发生酰化反应引入C=C键,其与角蛋白水解物分子自身结构中的巯基可发生巯基-乙烯基反应;同时在酰化反应过程中产生的甲基丙烯酸,也可与角蛋白中的巯基发生巯基-烯反应,结合角蛋白分子链之间的氢键等其它相互作用,从而得到多重交联的三维网状结构。3.设计了一种在负载养分的同时还可以提高KMA-Gel水凝胶热稳定性和机械性能的方法。将含氮磷钾的线性聚合物（PDMUP）半互穿负载于角蛋白凝胶网络结构中,制得新型半互穿角蛋白基水凝胶（KMA/PDMUP-Gel）,并将其作为缓释肥料。通过FT-IR、SEM、XPS和XRD鉴定了KMA/PDMUP-Gel分子结构,结果显示PDMUP成功半互穿负载于KMA-Gel中。热重实验和压缩实验结果表明PDMUP的引入可提高材料的热降解温度和压缩强度。利用紫外分光光度计和电感耦合等离子体测定KMA/PDMUP-Gel经水中和土柱仪中所释放的氮、磷和钾的含量,结果表明在KMA/PDMUP-Gel中,钾释放的最快,其次为磷,最后为氮。更多还原

【Abstract】 Tannery waste bovine hair is a kind of abundant keratin resource with low price.However,most of waste bovine hair is burned or landfill,resulting in resource waste and environmental pollution.Under the background of carbon peaking and carbon neutrality goals,how to utilize waste bovine hair is an important issue in leather industry.Waste bovine hair keratin can provide necessary nutrients for plant growth,because it contains nitrogen,phosphorus,sulfur and a variety of microelements.The approach of using waste bovine hair keratin as fertilizer is economical and reasonable.Recently,slow-release fertilizer hydrogel receive great attention due to its ability to retain water and the high efficiency of fertilizer.Therefore,according to the concept of circular economy,a new type of slow-release fertilizer hydrogel derived from waste bovine hair is developed in this thesis.In this paper,keratin（K-SH）was extracted by oxidation-reduction method.Then keratin-based hydrogel was prepared through reaction between K-SH and methacrylic anhydride（MA）,and the chemical crosslinking mechanism was studied.Finally,a novel semi-interpenetrating keratin-based hydrogel（KMA/PDMUP-Gel）,loading linear polymers containing N,P and K onto the network structure,was prepared.Also,the performance of KMA/PDMUP-Gel as slow-release fertilizers was investigated.The main works and conclusions are as follows:1.Keratin（K-SH）was extracted from waste bovine hair by oxidation-reduction method,and the effect of H₂O₂ oxidation time on the hydrolysis rate,relative molecular weight and active thiol group of K-SH were studied.With the increase of H₂O₂ pretreatment time,the solubility of bovine hair in the subsequent reducing solution is increased,but the molecular weight（Mn）and active thiol content of the obtained K-SH are decreased.Methacrylated keratin hydrogels（KMA-Gel）were synthesized via the reaction between methacrylic anhydride（MA）and K-SH（Mn=18160 g/mol and thiol content of 61.55 μmol/g.）The morphology,viscoelastic properties,mechanical properties,swelling properties and biodegradability of KMAGel with different proportions were investigated by changing the amount of MA.SEM images reveal that KMA-Gel is porous materials with three-dimensional network structure.The viscoelasticity behavior testing shows that the KMA-Gel displays elastic solid behavior in the linear viscoelastic region,and increasing the dosage of MA can improve the crosslinking degree of KMA-Gel network.Compression experiments show that the compressive strength of KMA-Gel is about 5.7 kPa,and KMA-Gel could quickly recover to its original states without breakage after 5 cycles.Swelling experiments show that KMA-Gel can be up to approximately four times its own weight after swelling in water.Moreover,KMA-Gel have good biodegradability.When the mass ratio of keratin to MA is 3:2,the comprehensive performance of KMAGel is the best.2.In this paper,MA was used to prepare KMA-Gel by cross-linking K-SH,and its crosslinking mechanism is not clear.This chapter focuses on the mechanism of gel formation.The first step is to establish a molecule model to determine the possible chemical cross-linking reaction between K-SH and MA.The molecular structure of K-SH contains cystine and cysteine,which were used as molecule model compounds to react with MA respectively to obtain samples with different proportions.The samples were characterized by FT-IR and ¹H-NMR to clarify the chemical crosslinking mechanism.The conclusions are as follows: the acylation reaction occurs between cysteine and MA to introduce vinyl groups into cysteine structure,and methacrylic acid（MAA）is produced at the same time.MAA firstly react with thiol groups of cysteine through thiol-ene reaction.Then self-crosslinking reactions occur between vinyl groups and thiol groups in cysteine structure.Secondly,soluble modified keratin（KMA）samples were prepared by reactions between different ratios of K-SH and MA to study the chemical cross-linking mechanism.The molecular structure of KMA was characterized by FT-IR,¹H-NMR and XPS and the conversion degree of amino and thiol groups of KMA were measured.Combined with the above molecule model,the chemical cross-linking mechanism of KMA-Gel is proposed:acylation reactions occur between the amino groups of the K-SH molecular chain and methacrylic anhydride to introduce vinyl groups,which can be reacted with thiol groups of K-SH via thiol-ene reaction.Meanwhile,methacrylic acid is formed during the acylation reaction,and it can also react with thiol groups of K-SH through thiolene reaction,combined with other interactions such as hydrogen bonds of keratin molecular chains,Thereby,methacrylated keratin hydrogels（KMA-Gel）with threedimensional network structure are obtained.3.In this chapter,a method is designed to improve the thermal stability and mechanical properties of KMA-Gel while loading nutrients.A novel semiinterpenetrating keratin based hydrogels（KMA/PDMUP-Gel）were prepared as slow release fertilizer by loading the linear polymer（PDMUP）of N,P and K into KMAGel.The structure of KMA/PDMUP-Gel were studied by FT-IR,SEM,XPS and XRD.The results show that PDMUP is successfully semi-interpenetrated into KMA-Gel.TG measurements and compression experiments show that introduce PDMUP into KMA-Gel is beneficial to improve its thermal stability and compressive strength.Slow-release performance of KMA/PDMUP-Gel in water and soil was determined by UV spectrophotometer and Inductively Coupled Plasma（ICP）.The results show that KMA/PDMUP-Gel has good slow-release properties.Potassium released by KMA/PDMUP-Gel is the fastest,followed by phosphorus and nitrogen.更多还原