ISSN:
1022-1352
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The network-forming behavior, gelation, and vitrification of lignin-polyether-copolymer-epoxide/amine resins were determined using a recently described dynamic mechanical thermal analysis (DMTA)-based method. Six resins were studied which differed in lignin content, polyether arm length, and molecular weight. Glass transition temperature (Tg)-cure time master curves could be constructed for cure temperatures ranging from 90 to 200°C; and semiexperimental vitrification plots were derived for each system based on the knowledge of activation energy and cure time at a reference temperature. The point at which the cure process becomes diffusion-controlled (i.e., vitrification) happens at lower extents of conversion for lignin-rich fractions. Near vitrification, the cure events change from n-th- to second-order kinetics, and this indicates a reduction in polyether-arm mobility. This suggests that the crosslinking of lignin centers with polyether arms produces a network in which the reactant-carrying flexible arms do not have sufficient free volume to react. The greatest increase in Tg during crosslinking is about 100°C for all molecular weight fractions, and this suggests that high-Tg networks can only be achieved with high-Tg prepolymers.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1994.021950106
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