Hatton Fiona L, Ruda Marcus, Lansalot Muriel, D'Agosto Franck, Malmström Eva, Carlmark Anna
KTH Royal Institute of Technology , School of Chemical Science and Engineering, Department of Fibre and Polymer Technology, Teknikringen 56, SE-100 44 Stockholm, Sweden.
CelluTech AB, Teknikringen 38, SE-114 28 Stockholm, Sweden.
Biomacromolecules. 2016 Apr 11;17(4):1414-24. doi: 10.1021/acs.biomac.6b00036. Epub 2016 Mar 7.
Herein, we report a novel class of latex particles composed of a hemicellulose, xyloglucan (XG), and poly(methyl methacrylate) (PMMA), specially designed to enable a biomimetic modification of cellulose. The formation of the latex particles was achieved utilizing reversible addition-fragmentation chain transfer (RAFT) mediated surfactant-free emulsion polymerization employing XG as a hydrophilic macromolecular RAFT agent (macroRAFT). In an initial step, XG was functionalized at the reducing chain end to bear a dithioester. This XG macroRAFT was subsequently utilized in water and chain extended with methyl methacrylate (MMA) as hydrophobic monomer, inspired by a polymerization-induced self-assembly (PISA) process. This yielded latex nanoparticles with a hydrophobic PMMA core stabilized by the hydrophilic XG chains at the corona. The molar mass of PMMA targeted was varied, resulting in a series of stable latex particles with hydrophobic PMMA content between 22 and 68 wt % of the total solids content (5-10%). The XG-PMMA nanoparticles were subsequently adsorbed to a neutral cellulose substrate (filter paper), and the modified surfaces were analyzed by FT-IR and SEM analyses. The adsorption of the latex particles was also investigated by quartz crystal microbalance with dissipation monitoring (QCM-D), where the nanoparticles were adsorbed to negatively charged model cellulose surfaces. The surfaces were analyzed by atomic force microscopy (AFM) and contact angle (CA) measurements. QCM-D experiments showed that more mass was adsorbed to the surfaces with increasing molar mass of the PMMA present. AFM of the surfaces after adsorption showed discrete particles, which were no longer present after annealing (160 °C, 1 h) and the roughness (Rq) of the surfaces had also decreased by at least half. Interestingly, after annealing, the surfaces did not all become more hydrophobic, as monitored by CA measurements, indicating that the surface roughness was an important factor to consider when evaluating the surface properties following particle adsorption. This novel class of latex nanoparticles provides an excellent platform for cellulose modification via physical adsorption. The utilization of XG as the anchoring molecule to cellulose provides a versatile methodology, as it does not rely on electrostatic interactions for the physical adsorption, enabling a wide range of cellulose substrates to be modified, including neutral sources such as cotton and bacterial nanocellulose, leading to new and advanced materials.
在此，我们报道了一类新型的乳胶颗粒，其由半纤维素木葡聚糖（XG）和聚甲基丙烯酸甲酯（PMMA）组成，专门设计用于实现纤维素的仿生修饰。乳胶颗粒的形成是通过可逆加成-断裂链转移（RAFT）介导的无表面活性剂乳液聚合实现的，该聚合使用XG作为亲水性大分子RAFT试剂（大分子RAFT）。在初始步骤中，XG在还原链末端进行功能化以带有二硫酯。受聚合诱导自组装（PISA）过程的启发，随后将这种XG大分子RAFT用于水中，并与作为疏水性单体的甲基丙烯酸甲酯（MMA）进行链扩展。这产生了具有疏水性PMMA核的乳胶纳米颗粒，其在冠层由亲水性XG链稳定。目标PMMA的摩尔质量有所变化，从而得到了一系列稳定的乳胶颗粒，其疏水性PMMA含量占总固体含量（5 - 10%）的22%至68%。随后将XG - PMMA纳米颗粒吸附到中性纤维素底物（滤纸）上，并通过傅里叶变换红外光谱（FT - IR）和扫描电子显微镜（SEM）分析对改性表面进行分析。还通过带耗散监测的石英晶体微天平（QCM - D）研究了乳胶颗粒的吸附情况，其中纳米颗粒被吸附到带负电荷的模型纤维素表面。通过原子力显微镜（AFM）和接触角（CA）测量对表面进行分析。QCM - D实验表明，随着存在的PMMA摩尔质量增加，更多的质量被吸附到表面。吸附后表面的AFM显示出离散的颗粒，在退火（160°C，1小时）后这些颗粒不再存在，并且表面粗糙度（Rq）也至少降低了一半。有趣的是，通过CA测量监测发现，退火后并非所有表面都变得更疏水，这表明在评估颗粒吸附后的表面性质时，表面粗糙度是一个需要考虑的重要因素。这类新型乳胶纳米颗粒为通过物理吸附进行纤维素修饰提供了一个极好的平台。利用XG作为纤维素的锚定分子提供了一种通用的方法，因为它在物理吸附中不依赖静电相互作用，能够对包括棉花和细菌纳米纤维素等中性来源在内的多种纤维素底物进行修饰，从而产生新型的先进材料。
