Viscoelastic behaviour of vinylic copolymers of cellulose and their glass transition temperature by DSC

Abstract

SYNOPSISThe viscoelastic response of some vinylic copolymers of cellulose prepared with vinyl acetatemethyl acrylate mixtures and with Ce( IV) ion as initiator, and native cellulose, were studied a t 110 Hz in a range of temperatures from -120-100°C.The viscoelastic spectrum of cellulose shows the @-relaxation that is not shown in its vinylic copolymers. We observed the same effect in the dielectric fi-relaxation.For the vinylic copolymers of cellulose, one viscoelastic relaxation attributed to the arelaxation of the grafted vinylic chains is observed. Some differences in the characteristics of this relaxation may be related to the composition of PVA/PMA vinylic side chains and to the ratio of cellulose in the copolymer. The plots of the Argand diagrams give us a better understanding of the viscoelastic behaviour of these materials. The results seem to indicate that the cellulose hinders the large-scale motions of the vinylic chains grafted onto it. The glass transition temperature ( T,) determined by differential scanning calorimetry (DSC ) also shows the same fact: the T, of the vinylic copolymers of cellulose are higher than both the T, of polyvinyl acetate-polymethyl acrylate copolymers ( PVA-PMA) without cellulose and the T, of some blends of cellulose and the PVA-PMA whose composition was as similar as possible to the cellulosic copolymers. The importance of the covalent bonds between cellulose and the vinylic side chains in the structural transitions are revealed. The present results are compared with the dielectric a-relaxation that we described elsewhere. 0 1993

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

“…The T g values are shown in Table II. These values are lower than the T g of the PVA alone, which is about 41.8°C, as determined previously,3 due to the presence of the PMA units in the grafted chains. In this way, copolymers CD1 and CB1 (AV/AM = 80/20) with higher PMA ratio, exhibit lower T g than copolymer CD2 (AV/AM = 85/15).…”

“…The first one has been assigned by other authors5–7 to motions of OH primary groups in the amorphous region of cellulose. The second peak at 10°C has been ascribed by other authors3 to the moisture absorbed in cellulose, but its origin is not clear.…”

“…Similar figures have been obtained for the other vinylic copolymers, CD1 and CB1. All these copolymers show a well‐developed process centered at 40°C, named α, which is attributed to the glass–rubber relaxation of the vinylic side chains,3, 7 because it does not appear in the cellulose.…”

“…The glass transition temperature T g values have been determined on the DSC curves as described in a previous work 3. The results are shown in Table II.…”

Reconstruction of histograms of the glass transition temperature of free radical copolymers from DSC thermograms

“…Although it is easy to reduce the phenomena after several temperature scans, a slight thermal effect generally remains at the end of the glass transition front, as a complete quench of the polymer is never fully achieved. A recent article19 on the viscoelastic behavior of vinylic cellulose copolymers underlines the fact that the application of regression lines for the determination of T g should take into account the possible relaxation phenomena of the material, because otherwise the T g values may be different from those of the same material without a relaxation peak. By taking into consideration the overshoots in the DSC diagrams that become more pronounced with physical aging (i.e., link 3 in Fig.…”