Method of increasing polymerization reaction rates in the production of a fiber-thermoplastic matrix by in situ bulk polymerization

In a method for the production of a moldable, fiber-thermoplastic polymer matrix wherein a fibrous web of less than 0.25-inch thickness and of less than 600 lbs./3,000 ft.sup.2 basis weight is saturated with a liquid-phase composition, comprising a vinyl monomer and a thermally activated polymerization initiator in an amount of 0.5-10% of said composition having a viscosity of less than about 10,000 centipoise, is subjected to heat and results in a matrix comprising at least about 25% polymer by weight of said matrix, the improvement wherein polymerization time is less than eight minutes, comprising:

• adjusting the monomer content of the saturated web to a total amount that is the sum of:
• (a) an amount sufficient to attain the desired polymer content by weight of the matrix at a temperature just equal to that necessary to cause sustained polymerization by said initiator, and (b) an amount 5-70% in excess of (a) wherein said excess amount significantly increases polymerization reaction rates such that a 25% polymer content by weight of the matrix is attained in less than eight minutes;
• contacting the composition-containing web with a first heat transfer surface maintained at a constant temperature sufficient to rapidly initiate and sustain polymerization but low enough such that the exothermic heat of polymerization is substantially absorbed;
• controlling monomer loss from said composition-containing web by, simultaneously with the heat transfer contacting step, contacting the surface of the web opposite the heat transfer surface with a flexible, vapor-impervious belt tensioned to ensure sealing contact of the belt and web against the heat transfer surface;
• and
• contacting said composition-containing web, after the desired polymer content by weight of the matrix has been attained, with a second heat transfer surface maintained at a constant temperature sufficient to remove the remaining monomer from the web through evaporation, including sustantially all of the excess amount (b).