【作者】 赵群；

【导师】 阎克路；

【作者基本信息】 东华大学 ， 纺织化学与染整工程， 2014， 博士

【摘要】 纳米微晶纤维素(CNCs)作为一种新型的生物质基高分子材料,在多个领域成为当前的研究前沿和热点,如何更好的发掘纳米微晶纤维素在这些领域中的应用,需要对其性质进行系统研究。结合水性聚氨酯和聚己内酯在众多领域中的应用及其所表现出的特殊性能,有效构建纳米微晶纤维素与这两种高聚物的复合材料,可以拓宽纳米微晶纤维素的应用领域及应用性能。论文研究了纳米微晶纤维素的制备及其改性方法,并将其与水性聚氨酯、聚己内酯两种可降解高聚物进行复合,通过研究复合材料的性能提出其应用潜力。首先以微晶纤维素(MCC)为原料,采用酸解法制备得到CNCs,通过对CNCs的酸解工艺条件的优化,得到酸解的最佳工艺条件为：MCC:H2SO4=1:8.75g/mL.硫酸浓度为63.5%(w/w)、酸解温度为45℃、酸解时间为110min,此工艺条件下得到的CNCs产率为37.09%。TEM照片显示CNCs长度基本在100-200nm之间,直径在10～20nm之间,多为棒状颗粒,且颗粒大小分布均匀。并且CNCs在水分散体系中能形成稳定的带蓝光透明悬浮液,在室温下长期放置不会出现分层或者沉淀现象,这是MCC所不具备的。XRD和TGA结果表明,与MCC相比,CNCs的结晶度略有提高,但是热稳定性能下降。水性聚氨酯作为一种无氯防毡缩整理剂,能在羊毛表面形成薄膜而覆盖羊毛纤维表面鳞片,但由于其成膜性和力学性能较差,要获得良好的防毡缩效果使用量很大,整理后织物变硬,严重影响羊毛的手感,因此需要对其进行改性。我们采用溶液浇注法制得水性聚氨酯／纳米微晶纤维素复合膜(WBPU/CNCs),对复合膜的形貌、分子基团、结晶性、热稳定性、力学性能等进行分析,探讨水性聚氨酯与纳米微晶纤维素分子之间的作用机理。同时,将这种复合乳液对羊毛织物进行防毡缩整理,研究并评估WBPU/CNCs复合整理剂在羊毛防毡缩整理中的效果。DMA结果表明,加入CNCs能有效提高WBPU的拉伸强度、杨氏模量和储存模量,对WBPU的增强效果明显。此外由于CNCs的加入可能会破坏WBPU中软段分子和硬段分子间的相互作用,导致WBPU分子中相分离程度增加,从而导致复合材料玻璃化转变温度降低。我们还对WBPU/CNCs的粘弹性行为进行了研究。通过频率扫描发现,加入CNCs后复合材料的弹性性能比纯基体有一定程度的提高,特别表现在高频区。弹性的提高同CNCs与WBPU分子链之间的相互作用有关,由此可以推断出CNCs在WBPU基体中形成一个网络,这种网络阻挠了高分子链的运动,从而使得材料不易变形,在低频区,这种网络的增强作用比较明显。用Power Law模型对储存模量E’和损失模量E"与频率之间的关系进行了深入分析,可以发现CNCs的添加能够增加WBPU-CNCs复合薄膜的静态粘弹性,但降低了纳米复合材料的动态粘弹性,并且加入CNCs会降低WBPU膜对频率的敏感性,因此有望扩大WBPU/CNCs的应用范围。用Burger’s模型进行数值模拟分析WBPU/CNCs复合材料的蠕变-回复性能,发现CNCs的加入可以增强复合材料的耐蠕变性能,这一结果再次说明了CNCs与WBPU之间存在着相互作用力。此外我们还发现,对于粘弹性高聚物来说,频率敏感性和蠕变-回复之间可能存在一定的关系。通过羊毛纤维表面的SEM图可以看到,WBPU/CNCs复合物在羊毛表面形成的膜更为饱满,甚至可以填充鳞片层的间隙,这说明CNCs的加入提高了聚氨酯成膜的力学性能,从而能提高羊毛的防毡缩性能和降低45%的WBPU防毡缩整理剂使用量,减少了对环境的污染,整理后纤维上膜变薄且强力提高,因此对织物的手感也有所改善。无法分散在有机溶剂中并且经冷冻干燥后会发生不可逆团聚是现在CNCs应用面不广的主要因素之一,鉴于此,我们研究了反胶束增溶CNCs和化学改性CNCs两种方法,以提高其在有机溶剂中的分散性。同时,又由于聚己内酯PCL机械性能较差,降解时间长,我们将改性后的CNCs与PCL共混成膜,研究CNCs对PCL性能的影响。反胶束内具有极性的“水池”,利用这个水池可以直接将浓缩的CNCs水分散液增溶在氯仿中,从而可以避免冷冻干燥引起的不可逆团聚。我们先通过研究最大增溶水量筛选表面活性剂和助表面活性剂的种类和浓度,确定了选用OP-7/正辛醇／氯仿为反胶束体系,表面活性剂OP-7的浓度为0.02g/mL,助表面活性剂为正辛醇,且与OP-7的质量比为3：2,此条件下增溶水量W0为237.36。然后根据粒径测试结果,我们提出CNCs在OP-7/正辛醇／氯仿反胶束体系中的状态模型：反胶束体系不同于常见的圆形体系而是棒状体系,因此可以将棒状的CNCs包裹在“水池”中,从而稳定分散在氯仿中。PCL/RCNCs复合膜XRD和热力学测试结果表明CNCs表面的羟基与PCL分子链的羰基形成了氢键,阻碍了分子链的运动,导致PCL结晶度的下降；DMA和力学测试结果表明CNCs对PCL复合膜具有增强效果。接触角测试结果表明,RCNCs的加入可以提高PCL膜的亲水性、加快PCL的降解速度。但是,受反胶束最大增溶水量的限制,CNCs在PCL中最多只能添加1.08%,为了提高CNCs在PCL中的含量,我们接下来又采用十八烷基异氰酸酯结合原位溶剂交换的方法对CNCs进行改性得到C18-CNCs,并将改性后的CNCs与PCL溶液浇注成膜,制得一系列不同C18-CNCs含量的PCL/C18-CNCs纳米复合膜,通过研究复合膜的性能探讨其应用潜力。首先采用元素分析法计算不同反应条件下产物的取代率,确定了十八烷基异氰酸酯与CNCs反应的温度和时间分别为110℃,40min,此时取代率最高,为0.0923。TEM照片显示十八烷基异氰酸酯对CNCs的改性没有改变CNCs的形貌和晶型,仍为棒状,长度在200nm左右直径在10-20nm之间；并且由于采用的溶剂交换过程,避免了事先对CNCs进行干燥,因此C18-CNCs在氯仿中分散均匀,没有明显团聚现象。力学性能测试发现C18-CNCs含量在PCL/C18-CNCs复合膜中含量不超过6wt%时,其分散性较好,复合膜拉伸强度增加了约148%；当含量高于6wt%时,C18-CNCs易发生团聚,导致复合膜强力下降。接触角测试结果表明C18-CNCs的添加能提高PCL膜的疏水性能,增强复合膜对水蒸汽的阻隔性能。更多还原

【Abstract】 As a novel biomass-based polymer material, cellulose nanocrystals (CNCs) is becoming one of the current research frontiers in many areas. In order to explore its application in these areas, we need to make a systematic study on its properties. Combined exceptional performance of water-borne polyurethane (WBPU) and polycaprolactone (PCL) in many fields, we composite cellulose nanocrystals with these two kind of polymers which can broaden the application areas of cellulose nanocrystals. Preparation and modification methods of cellulose nanocrystals are studied in this paper and we raised its potential applications by researching properties of its reinforced composites.The cellulose nanocrystals were prepared by acid hydrolysis of cellulose microcrystalline (MCC). We used single factor experiments-orthogonal experiment-single factor experiment method to optimize CNCs acid hydrolysis process conditions. The finally optimized conditions were:MCC:H2SO4=1:8.75g/mL, H2SO4concentration was63.5wt%, temperature was45℃, and acid hydrolysis time was110min, CNCs yield was37.09%in this condition. TEM images showed that the CNCs was in rod form with lengths of70-150nm and diameters of10-20nm in aqueous suspension, respectively. CNCs dispersed stably in aqueous dispersion with blue transparent, long-term placement at room temperature which is not available in MCC. XRD and TGA results show that compared with the MCC, the degree of crystallinity of CNCs increased, but its thermal stability decreased.As a chlorine-free polymer and coating agent, WBPU has a better anti-felting effect for wool fabrics. However, the higher concentration of WBPU was usually employed in practice in order to form a durable film and cover the scales of the surface of wool fibers. So that the WBPU concentration is high and the handle of finished fabric is hard, which limits its application. After the two aqueous suspensions were mixed homogeneously, cellulose nanocrystal reinforced polyurethane composite (nanocomposite) films were prepared and evaluated by means of transmission electron microscopy, scanning electron microscopy and dynamic mechanical analysis. Then the nanocrystal films were applied onto surfaces of wools by a pad-dry-cure process with nanocomposites containing different cellulose nanocrystal contents.DMA results showed that storage modulus and loss modulus of WBPU/CNCs composites films increased with CNCs content increasing. And because the CNs can improve the microphase separation between soft and hard segments in WBPU, Tg decreased with increasing of CNs content. Besides that, we studied viscoelastic properties of WBPU/CNCs composites films. In frequency sweep tests, the E1and E" were recorded and modeled by the Power Law equation. CNCs precipitation significantly increased the steady state viscous properties of cellulose nanocomposites films but decreased the dynamic viscoelastic properties of nanocomposites and frequency sensitivity. In the creep-recovery tests, the data were fitted to Burger’s model. The E2value and η1value in Burger’s model were increased by incorporating CNs. To the contrary, however, the relaxation time t2was decreased. It means CNs can improve WBPU’s creep resistance property. This result showed interactions existed between CNCs and WBPU once again. In additional, we also found that the frequency sensitivity and creep-Replies may exist between certain relationship.The anti-felting results indicated that with increasing cellulose nanocrystal content from0to1.0wt%, the area-shrinking rate of the treated wool fabrics was decreased from5.24%to0.70%, and the tensile strength of the fabric was increased by14.95%and decreased about45%use of waterborne polyurethane. The pure WBPU of concentration in50g/L covered surfaces of the fibers reveal a thin layer covering the scales of wool fibers, which improves the smoothness of the fibers. The WBPU coating the cellulose nanocrystals provided a relatively intact layer of coating covering the surfaces of the wool fibers, higher amounts nanoparticles absorbed on the surface of wool and, consequently, the ups and downs of the surface of wool covered completely which could further decrease Directional Frictional Effect (DEF) of wool fabrics and improve antifelting effect.Dispersed in organic solvent poorly is one of main problems of CNCs which restrict its application. So, we modified CNCs using a reverse micelle method and the chemical surface modification method in order to improve its dispersibility in organic solvents. At the same time, because PCL has poor mechanical properties and degradation for a long time, it can’t meet the bone defect repair and fracture fixation material mechanical requirements, we blended modified CNCs and PCL to form nano-composite films and studied these films’ performance.Reverse micelle has a polar "pool", we make use of this "pool" to solubilize concentrated CNCs aqueous dispersion in chloroform so that irreversible agglomeration was avoided which was caused by freeze-drying process. Firstly, the OP-7/n-octanol/chloroform reversed micelle system was chose by investigating the influences of the type and concentration of surfactants cosurfactant on the water solubilization of the reversed micelle system. The concentration of OP-7was0.02g/mL, octanol was cosurfactant and its mass ratio with OP-7was3:2, the solubilization Wo was237.36. Then, according to particle size test, we proposed CNCs in OP-7/n-octanol/chloroform reverse micelles state model:rod CNCs wrapped in rod reverse micelles. Finally, the XRD and mechanical test results show that with the increasing of RCNCs content, the degree of crystallinity, melting temperature of RCNCs/PCL composite material were decreased; With the increasing of the RCNCs, the degradation rate and the hydrophilic of RCNCs/PCL composite material increased.But, due to the limitation of the reversed micelle system’s solubilization, the adding amount of modified RCNCs was very small, no more than1.08%, so the chemical-in situ solvent exchange method was used to modify CNCs, choosing octadecyl isocyanate as chemical modification reagent. The CNCs chemical modification process was studied through the calculation of the graft rate of the product. By means of infrared spectrum analysis and static method, the properties of C18-CNCs were characterized. The results showed that C18-CNCs has good dispersion in chloroform. C18-CNCs/PCL composite material was prepared by compounding C18-CNCs and PCL. By means of Fourier transform infrared spectrum, X-ray diffraction, DSC test analysis, scanning electron microscopy (SEM) analysis, mechanical properties test and hydrophilic test, the properties of PCL/C18-CNCs composite material were characterized, and the content of C18-CNCs influence on PCL/C18-CNCs composite material performanee was also investigated. The results showed that with increasing of C18-CNCs, the tensile strength and the hydrophilic of PCL/C18-CNCs composite material increased, but the degree of crystallinity, glass transition temperature, melting temperature of PCL/C18-CNCs composite material first dropped down, when the content of C18-CNCs was6.0%, all reached the minimum value, with the content of C18-CNCs going on increasing, the degree of crystallinity, melting temperature of C18-CNCs/PCL composite material raised up. Scanning electron microscopy (SEM) analysis showed that, when the content of C18-CNCs was below6.0%, it can be evenly distributed on the surface of C18-CNCs/PCL composite membrane, when the content of C18-CNCs was more than6.0%, it gathered together on surface of C18-CNCs/PCL composite membrane.更多还原