Vinylic graft copolymers of cellulose. I. Effects of monomer concentrations and crystallinity index of cellulosic substrate on grafting vinyl acetate onto cotton

Abstract

SYNOPSISGraft copolymerization of vinyl acetate (VA) and methyl acrylate ( M A ) on cotton cellulose was initiated by the Ce (IV) ion, and ungrafted vinylic polymer was separated from the graft copolymer by acetone extraction. The influence of the ratio aqueous initiator solution volume/monomeric volume ( Vaq/VmOn), vinyl acetate volume/methyl acrylate volume ( VVA/ VMA), and the cellulose crystallinity index (CI ) on the grafting reaction were studied. To modify the crystallinity of cellulose, native cotton was treated with NaOH in the concentrations 10, 15, and 20% (mercerized). The viscosimetric average molecular weight ( M u ) , the polymerization degree (PD) , and the crystallinity index proposed by Nelson and O'Connor (CI) were determined for native and NaOH-treated cotton. The polymeric side chains grafted were separated from the cellulose backbone by acid hydrolysis in 72% H,SO,. The viscosimetric average molecular weight ( M u ) was determined, and the number of vinylic chains per cellulosic chain (graft frequency, G F ) were calculated. The grafting percentage, %G, was higher for most amorphous cellulose and for a higher methyl acrylate percentage (%MA) in monomeric reaction mixtures (VA-MA). The Vaq/Vmon ratio that yields the highest %G was 70/30. The increase of the %G with the %MA in the VA-MA monomeric mixture seems to be due to both an increase in the length of vinylic grafted chains (as shown by its M u ) and the number of grafted chains ( G F ) . The increase in the %G when the crystallinity index (CI) of the cellulosic substrate decreases seems to be due to an increase in the length of the vinylic grafted chains, but not to an increase in the number of grafted chains, since the Mu increases and GF decreases when the CI of cellulose decreases.

Biodegradation studies of cellulose and its vinylic graft copolymers by thermal analysis and mechanical spectroscopy

“…Table VI shows the Vogel parameters and the apparent activation energy for the α‐relaxation of the undegraded vinylic copolymers of cellulose. The obtained apparent activation energy is higher for the CB1(136%G) and CD2 (184%) copolymers whose cellulosic substrate has a higher crystallinity index, its vinylic chains are shorter, and its grafting frequency lowest, as our previous results 2. Between CD1 (305%G) and CD2 (184%G) copolymers with the same cellulosic substrate, the CD1copolymer, with a higher PMA/PVA ratio and longer vinylic chains than CD2, shows lower activation than CD2.…”

“…The vinylic graft copolymers of cellulose were obtained by the Ce (IV) method as we described in a previous work 2. For this work we have selected copolymers with two different cellulosic substrates prepared by treatment with a 10% NaOH solution (Cel.B) and a 20% NaOH solution (Cel.D).…”

“…The grafting percentages were determined for all the copolymers (Table I). It is also known that the grafting frequency decreases as CB1 > CD1 > CD2 and the vinylic chain length CD1 > CD2 > CB1 2. Samples of 2.5 × 1 cm were cut to be submitted to a laboratory soil burial test.…”

“…In this article vinylic copolymers of cellulose were prepared by graft polymerization of vinyl acetate (VA) and methyl acrylate (MA) on cotton cellulose initiated by the Ce (IV) ion method 2. Different cellulosic substrates obtained from purified cotton cellulose treated with NaOH solutions of different concentrations (10 and 20%) were treated with different volumetric ratios of monomers VA/MA (80/20 and 85/15) to achieve different graft percentages (% G ), which are due to the vinylic chains length and/or to the grafting frequency.…”

Grafting of poly (methyl acrylate) onto sulfite pulp fibers and its effect on water absorbance

“…The grafted polymer chains were isolated from backbone polymer by treatment with 72% sulfuric acid following the process described by Flaque and Montserrat 15…”