Frank Edward Critchfield

Chemical Reaction Sequence in the Formation of Water-Blown, Urethane Foam

Water-blown urethane foaming is a process which leads in a matter of minutes to the production of highly &dquo;engineered,&dquo; supramolecular architecture of foam from a mixture of relatively low molecular weight components. This making of urethane foam is one of the few industrial processes in which rapid polymerization occurs in such a controlled way that polymerization and supramolecular structure are achieved almost simultaneously. In order to understand this remarkable transformation, it is necessary to define the chemical species present and the order in which these species react. By inference from the highly involved structure produced, the order and timing of these reactions is critical. In this paper, this sequence of reactions is defined and related to the physical stages of foaming evident from rise-profile and &dquo;gel-profile&dquo; measurements. From these studies, a clearer understanding is possible of the measurement of &dquo;gel-profile.&dquo;

Kinetics and Catalysis of Urethane Foam Reactions

Since the rates of chemical reactions in volved in cellular urethane formation are decisive for product quality, model reactions were kinetically investigated and the mech anism of catalysis was studied. A simple rela tionship found between the specific rate con stant and the molar ratio of alcohol/catalyst for an alcohol/isocyanate reaction catalyzed by stannous octoate suggests the formation of an activated intermediate complex. The balance between the alcohol/isocyan ate and water/isocyanate reaction rates is important. Organotin compounds promote the former rate more than the latter whereas the reverse holds for amine catalysts. The rates of both reactions, catalyzed by amines with and without stannous octoate as co catal yst, demonstrate a synergistic effect ex plained by the extra stability imparted to the activated intermediate complex by attach ment of the amine.

Polymer/Palyols, a New Class of Polyurethane Intermediates

Research and Development Department South Charleston, West Virginia 25303 number of new polyol compositions were synA thesized and evaluated as raw materials for urethane elastomers and foams. These compositions, termed POLYMER/POLYOLS, are part of the continuing search for materials which will impart superior properties to urethane flexible foams, and represent a significant advance in the technol-

Silane Effects and Machine Processing in Reinforced High Modulus Rim Urethane Composites

The demand of fuel economy for reduced motor vehicle weight has led to widespread interest in high modulus reaction injection molded urethane (RIM) for automotive exterior parts as well as for many non-automotive applications. Reinforcing fibers and fillers, combined with the versitility of urethane chemistry, are important parameters for achieving composites with stiffness and toughness while reducing coef ficients of thermal expansion.

Reaction Injection Molding: Filling of a Rectangular Mold

The present trend in fascia reaction injection molding is to ward larger, more complex parts and faster reacting systems. This has lead to short shot problems. To study this, slow motion movies were taken of filling and flow around objects in a transparent plaque mold with fascia type urethane formulations. Mold pressure and temperatures were recorded simultaneously. For fill times less than a characteristic reaction time, pres sures can be predicted assuming constant viscosity during filling. For filling times greater than the characteristic reaction time, weld lines and short shots can occur. Criteria for good filling based on the dimensional analysis of the flow field equations are developed. Flow front instability was ob served for high flow rates.

RIM Urethanes Structure/Property Relationships for Linear Polymers

Reaction Injection Molding (RIM) technology represented the major break-through in the polymer processing development of the seventies. This technology, based on the rapid mixing of co-reactive streams and subsequent feeding of the mixture into the polymerization reactor — the mold, — allows for production of large and intricate parts. The relatively low energy input that is required makes this technology especially attractive for today’s needs.

Dynamic Mechanical Properties of Liquid Reaction Molded Polyurethanes

HE AUTOMOTIVE INDUSTRY has recently introduced the &dquo;soft face&dquo; concept to Tcomply with Federal regulations on low speed impacts and to provide the consumer with damage protection. The basic components of the soft face consist of an elastomeric covering behind which is an energy management system to dissipate the kinetic energy of an impact. In order for polymers to be useful in the soft face application they must have a high, but temperature insensitive modulus over the use range, -20°F to +140°F, while maintaining flexibility and resistance to impact damage. The polymers in this investigation were designed to be produced by a relatively new process currently being referred to as Liquid Reaction Molding (LRM). LRM is basically the in situ molding of highly reactive liquid components, generally urethane intermediates. The objective of this investigation was to examine the LRM elastomers by dynamic mechanical measurements in order to assess the influence of their structures