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The role of resol fortifiers in latex wood adhesives

The role of resol fortifiers in latex wood adhesives Static and dynamic rheological analyses using time/temperature equivalence were applied to freestanding poly(vinyl acetate-co-NMA) adhesive films and to wood-bonded films (composites), which were completely dry in all cases. Films and composites were prepared with two types of cross-linking: (1) cross-linking through AlCl 3 catalysis of N -methylolacrylamide (NMA) comonomer; and (2) additional cross-linking using a resol phenolic (PF) additive, in addition to AlCl 3 catalysis. Rheological experiments revealed that accelerated weathering (AW) significantly modified the mechanical response of films and composites lacking the PF additive. For samples lacking PF fortifier, AW caused a new thermal transition appearing as a major mechanical softening in the long time domain (creep master curves) or in the low-frequency region (dynamic master curves). This new transition correlated to a performance loss found with fracture testing in a previous publication. Here, the static and dynamic rheological data indicated that the AW-induced softening was a reversible transition. Differential scanning calorimetry analysis and the manipulation of physical aging effects demonstrated that the AW-induced softening was a glass transition. The calorimetric weakness and temperature of this transition indicated that it corresponds to the T g of poly(vinyl alcohol) (PVOH), which is the emulsion polymerization interfacial agent. In contrast, all PF-formulated samples displayed only the base polymer T g . Therefore, the PF additive prevented weathering effects that lead to PVOH softening. Atomic force and scanning electron microscopy provided visual evidence of the action of PF on PVOH at interparticle boundaries. We suggest that the PF fortifier enhances latex durability through the formation of hydrolytically stable PVOH cross-links at the interparticle boundaries. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Holzforschung - International Journal of the Biology, Chemistry, Physics and Technology of Wood de Gruyter

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References (5)

Publisher
de Gruyter
Copyright
©2006 by Walter de Gruyter Berlin New York
ISSN
0018-3830
eISSN
1437-434X
DOI
10.1515/HF.2006.093
Publisher site
See Article on Publisher Site

Abstract

Static and dynamic rheological analyses using time/temperature equivalence were applied to freestanding poly(vinyl acetate-co-NMA) adhesive films and to wood-bonded films (composites), which were completely dry in all cases. Films and composites were prepared with two types of cross-linking: (1) cross-linking through AlCl 3 catalysis of N -methylolacrylamide (NMA) comonomer; and (2) additional cross-linking using a resol phenolic (PF) additive, in addition to AlCl 3 catalysis. Rheological experiments revealed that accelerated weathering (AW) significantly modified the mechanical response of films and composites lacking the PF additive. For samples lacking PF fortifier, AW caused a new thermal transition appearing as a major mechanical softening in the long time domain (creep master curves) or in the low-frequency region (dynamic master curves). This new transition correlated to a performance loss found with fracture testing in a previous publication. Here, the static and dynamic rheological data indicated that the AW-induced softening was a reversible transition. Differential scanning calorimetry analysis and the manipulation of physical aging effects demonstrated that the AW-induced softening was a glass transition. The calorimetric weakness and temperature of this transition indicated that it corresponds to the T g of poly(vinyl alcohol) (PVOH), which is the emulsion polymerization interfacial agent. In contrast, all PF-formulated samples displayed only the base polymer T g . Therefore, the PF additive prevented weathering effects that lead to PVOH softening. Atomic force and scanning electron microscopy provided visual evidence of the action of PF on PVOH at interparticle boundaries. We suggest that the PF fortifier enhances latex durability through the formation of hydrolytically stable PVOH cross-links at the interparticle boundaries.

Journal

Holzforschung - International Journal of the Biology, Chemistry, Physics and Technology of Woodde Gruyter

Published: Aug 1, 2006

Keywords: differential scanning calorimetry (DSC); field emission-scanning electron microscopy (FE-SEM); latex adhesives; parallel-plate rheology, phenol-formaldehyde; static and dynamic mechanical analyses (SDMA)

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