SEDL / STP / STP997-EB / STP26401S

Determination of the Degree of Mixing of Sheet Molding Compound Paste Using Thermogravimetry

Kau, H-T
Research engineer, Polymers Dept., General Motors Research Laboratories, General Motors Technical Center, Warren, MI

Pages: 19    Published: Jan 1988

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Abstract

Sheet molding compound (SMC) technology is used for manufacturing large composite automobile parts. To produce high quality composites, it is important to ensure that the compound paste is uniformly mixed.

A procedure based on thermogravimetry (TG) was developed to determine the uniformity of mixing of SMC paste and of samples molded from the paste. Batches of pastes prepared in the laboratory had a scale of uniformity of 100 μm based on the variance of the inorganic solid (calcium carbonate or CaCO³ filler) content. For paste samples containing a high concentration of volatile component, the accuracy of the analysis was affected by weight loss during the sampling procedure. Premolding the sample was an effective way to overcome this problem and to improve the accuracy.

TG was also used to investigate a procedure for compounding glass flakes in SMC paste. The results showed a high degree of nonuniformity in the slurry material. This was attributed to incomplete wet-out of the glass flakes.