Misel Arayüzü Polimerizasyon Yöntemi İle Mikrokristal Selüloz Yüzeylerin Sulu Ortamda Hidrofobik Modifikasyonu ve Karakterizasyonu

Abstract

Nowadays, plastics account for a significant fraction of municipal solid waste. Significant amount of these plastic wastes are polyolefins: LDPE, LLDPE, HDPE, PP, PET, PS and PVC. Recovery of these polyolefins for recycling causes reduction in their mechanical strength. This situation limits their use in a number of applications. If recycled polyolefins are combined with natural fibers in a composite structure, their mechanical properties can be improved substantially. By this means, their usage areas and market share can be extended while their fraction of solid waste can be reduced. In the use of natural fibers in composites, incompatibility between hydrophilic fibers and the hydrophobic polymers results in a poor compatibility and in poor ability to transfer stress from the matrix to reinforcing fiber. Among many uses of cellulose, it also commonly serve as natural fiber in polymer composites. Because of its polarity and hydrophilicity, cellulose is less compatible with hydrophobic and nonpolar polyolefins. This causes poor dispersion of fillers and weak interaction between matrix and cellulose filler. Cellulose fiber composites can also have poor mechanical properties due to swelling. Cellulose's hidrophilicity renders its potential usage as a filler. The aim of this study is to reduce the hydrophilicity of cellulose surface and increase the compatibility of cellulose with polyolefins as well as its usage in composites. Although many hydrophobization methods applied to cellulose in literature, admicellar polymerization, an easy, clean and cost efficient method that comprises water as a solvent, and less purification steps, has not been investigated adequately, yet. Thus the subject of this thesis work is using admicellar polymerization in hydrophobization of microcrystalline cellulose, in order to obtain a coast efficient, water and moisture resistant filler. The product can be used as micro filler in polyolefin based composites and in applications of hidrophobic cellulose. By use of ammonium persulfate as an initiator, microcrystalline cellulose (MCC) surface is modified with PMMA and PnBMA polymers by admicellar polymerization. Percent modification yield is gravimetrically investigated for each modification parameter. ATR - FTIR analysis are carried out to characterize surface functional groups of modified polymers. Water contact angle of MCC surface is increased from 33.5° to 57.0° by modification. TGA is used for investigation of the thermal decomposition of pure MCC, modified MCC and modified polymers alone. By XPS analysis, the elements of alkyl methacrylates modified on surface, are analyzed. With SEC measurements, molecular weights, molecular weight distributions and polydispersity indexes of surface polymers are investigated. PDI's are measured 1.87 and 1.46 for PMMA and PnBMA polymers, respectively. Glass transition temperatures of PMMA and PnBMA polymers measured as 82° and 21° by DSC measurements. Finally by SEM analysis, the topography of PMMA and PnBMA modified MCC surface is revealed that surface modifications are successfully achieved.