Synthesis and characterization of cationically and anionically modified poly(vinyl alcohol) microfibrils

["Polyvinyl alcohol", "Fibers", "Polymers", "PVA stereoregularity", "Dissertations -- Polymer science", "Theses -- Polymer science", "Chemistry and Polymer Science"]

Chirowodza, Helen ; Sanderson, R. D.

Stellenbosch University

Others  :  https://scholar.sun.ac.za:443/bitstream/10019.1/2184/1/chirowodza_synthesis_2009.pdf

瑞士|英语

来源: Stellenbosch University

【 摘 要 】

In papermaking, the addition of filler can be detrimental to the properties of the resultingpaper hence the use of additives that enhance paper properties are of paramount importance.Syndiotacticity rich poly(vinyl alcohol) (PVA) microfibrils were prepared for use as fillerretention aids. They were prepared via in situ fibrillation during the saponification of highmolecular weight poly(vinyl pivalate). The resulting fibers had high thermal stability andcrystalline melting temperature. They were not fully soluble in water even at 100 oC. In orderto make them less water resistant the syndiotacticity of the PVA microfibrils was varied bycopolymerizing vinyl pivalate with vinyl acetate and saponifying the resultant copolymer. Itwas observed that changes in syndiotacticity had a significant effect on the crystallinity,morphology and thermal properties of the resultant PVA.The surfaces of the fibers were modified by first crosslinking using glyoxal (a dialdehyde),and then attaching cationic and anionic groups by grafting and by carboxymethylation.Crosslinking prior to modification was beneficial in minimizing the solubility of the fibers inthe aqueous media in which they were modified. Heterogeneous modification techniques wereemployed so that fiber properties could be preserved. Carboxymethylation was carried outusing the two step Williamson's ether synthesis. The first step involves the formation of ahighly reactive alkoxide by the reaction of PVA with a strong base and the second itsetherification using a functional alkyl halide. Poly(methacryloyloxy ethyl trimethylammonium chloride) and poly(acrylic acid) were grafted from the PVA microfibrils using theKPS/Na2S2O3 redox initiation system. Grafting was confirmed by FTIR and NMRspectroscopy.Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were carriedout on both modified and unmodified PVA microfibrils. The results showed that crosslinkingresulted in an enhancement of the thermal properties of the microfibrils. A decline in the onsettemperature for thermal degradation and crystalline melting temperature were observed, andwere attributed to the modification of the PVA microfibrils.