Study On Modification Of Ramie Fiber Via Atom Transfer Radical Polymerization

Abstract: Atom transfer radical polymerization (ATRP) has been expanding continuously, since it was discovered in 1995, with a large effort being directed toward both better Understanding of the reaction mechanism and enlargement of the fields of application. Presently, most vinyl monomers can be polymerized in a "living"/controlled manner by using this technique, the main exceptions being vinyl acetate and vinyl chloride. Also, an increasing number of transition metals, like copper, ruthenium, iron, nickel, rhodium, and rhenium, in conjunction with different ligands can be used to catalyze the polymerization reaction.ATRP is a new and efficient route for synthesizing polymers with well controlled molecular weight, low polydispersity, and novel architectures. The ATRP has previously been utilized for "grafting from" processes from silicon, gold and silica surfaces. Grafting polymers to cellulose surfaces by the ATRP has been previously reported only in a limited number of papers. Daly et al. were the first to report a "living"/controlled polymerization technique applied to cellulose when polystyrene was grafted on cellulose. The ATRP is a robust and versatile technique to accurately control hain length and polydispersity.Natural fibrous materials have held a key role in the worldwide chemical and textile industries. Ramie fiber (also called China Grass), which is composed mainly of cellulose, is one of the oldest textile fibers with unique striking properties such as high air perviousness, and good antibacterial ability. However, in some aspects, the property of ramie fiber is inferior to the synthetic polymers. Thus, the modification of ramie fiber has attracted great attention and has continuously been pursued for improving its desired properties. Due to its high crystallinity and high degree of orientation, currently it is still a challenge work for the modification of ramie fiber. Since the invention of ATRP in 1995, it has been extensively investigated as a robust and versatile technique to synthesize polymers for "grafting from" processes with accurately controlled chain length and polydispersity. Previous reports on grafting polymers to natural cellulose substrates by ATRP were scarce, and filter paper as the substrate was exclusively used for a demonstration purpose. To the best of our knowledge, there was no report on grafting polymers to ramie fiber. The main contents of this thesis are as follows:1. As the contact angle of the ramie fiber is 75.9°, the ramie fiber has low hydrophobic property. If we want to make the hydrophobic of the ramie fiber become higher, we need a substance that has well hydrophobic to graft onto the surface of the ramie fiber. The poly(methyl methacrylate) is a polymer with well hydrophobic, the methyl methacrylate was grafted onto the surface of ramie fiber to change the hydrophobic via atom transfer radical polymerization in this study. The optimal reaction conditions for preparing the macroinitiated ramie fiber are determined to be the temperature of 60℃, and the reaction time of 24 h. The grafted copolymers were analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy and energy dispersive analysis of X-ray (SEM/EDAX); gelatin pervasion chromatogram (GPC), and thermogravimetric analysis (TGA). Results indicate that poly(methyl methacrylate) (PMMA) was covalently bonded onto the surface of ramie fiber, and the polymerization of MMA is a "living"/controlled process under the investigated conditions. Results of contact angle measurements indicate that the hydrophobic of the ramie fiber became high hydrophobic.2. The covalent bonding of tertiary amine 2-(dimethylamino)ethyl methacrylate (DMAEMA) to ramie fiber via atom transfer radical polymerization (ATRP) was studied using a brominated initiator and a catalyst of CuCl/1,10-phenanthroline. Results reveal that the poly(DMAEMA) (PDMAEMA) was successfully immobilized on the surface of ramie fiber in a controlled/living mode. After grafting with PDMAEMA on ramie fiber, the crystal structure of cellulose I for ramie fiber was still preserved and the lateral size of the microfibrils calculated based on plane 002 was slightly increased. As a demonstration of applications, the modified fiber was dyed with C.I. reactive red 2. The dye uptake, which almost linearly increased with the increase in molecular weights of the PDMAEMA attached on ramie fiber, was raised to be over 15 times of the raw fiber. The reason is explained as that the tertiary amines in PDMAEMA were protonated into quaternary amines, which facilitate the fix of the anionic dye on the ramie fiber.