Date of Award

2009

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Douglas J. Gardner

Second Committee Member

Adriaan van Heingingen

Third Committee Member

Raymond Fort

Abstract

The overall objective of this dissertation was to study the surface energy and acid-base characteristics of natural fibers, glass, a wood extract, and a sheet molding compound prepreg to facilitate the fabrication of totally synthetic and partially renewable sheet molding compounds (SMCs). The water absorption and micro-mechanical performance of the totally synthetic and partially renewable SMC composites were compared through accelerated aging experiments. Reinforcing glass sized for polyester, bast kenaf fibers, hot water extract from Acer rubrum, and a dicyclopentadiene modified polyester prepreg were analyzed by inverse gas chromatography to evaluate and help predict how the various components may interact in a crosslinked composite SMC. Dynamic Mechanical Thermal Analysis (DMTA) was used to determine how the components in the SMC changed as a function of hygrothermal aging by analyzing the glass transitions of the individual components in the SMC. Inverse gas chromatography (IGC) results indicated that the polyester prepreg material had an experimental dispersive surface energy value of 47 mJ/m2 that compared well with a rule of mixture analysis of the components in the SMC giving a value of 50 mJ/m2 both at 30?C. IGC results also indicated that the kenaf-prepreg material has a higher acid base interaction then the glass-prepreg material. The IGC results indicated that surface sizing of the kenaf fibers with styrene-maleic anhydride might improve the cohesiveness of the final kenaf based SMC. IGC results also indicated that hot water extract from Acer rubrum had a dispersive energy close to polystyrene and should be miscible in the prepreg material. Hygrothermal aging was done by soaking SMC samples at 70?C for 3, 168, and 1032 hour time intervals. Standard SMC fabricated with glass reinforcement had water uptakes of less than 5 weight percent after 1032 hours. SMC fabricated with kenaf had water uptakes at 1032 hours approaching 20 weight percent indicating the kenaf based SMC is not suitable for exterior applications or applications where water contact occurs. SMC fabricated with hot water extract from Acer rubrum had water uptake similar to, and in some cases, better then the standard SMC references. DMTA results indicated that thickening reactions took place without thickening agents in the SMC in the presence of excess absorbed water. The temperature range of –50?C to 260?C during DMTA testing effectively destroyed the kenaf based SMC. The glass based synthetic SMC was the most resilient to the heat ramps followed by the extract based SMC. Inverse gas chromatography is a useful tool for analyzing the dispersive and acid-base properties of components of a composite. Kenaf based and extract based SMC’s can be fabricated and the extract based SMC’s compare well with standard synthetic SMC’s for water absorption and micro-mechanical properties.

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