14 PIGMENT AND RESIN TECHNOLOGY November 1991 Letter fro m America by Paintman USA Estimating strength of bond between matrix resin and capacity of 30 million pounds a year, after considering technical capabilities, on-line quality control, problem fibre reinforcement solving capacity and the safety records of each firm. Estimates of the strength of the bond between the matrix The result of this partnership is a high-performance resin and the fibre reinforcement in polymer-matrix composites can now be made by a non-destructive resin which is said to be setting new standards for technique recently patented by Wen-li Wu , a scientist at recycled materials and is ideally suited for monolayer the National Institute of Standards and Technology, blow moulding of household chemical, motor oil other Gaithersburg, Maryland. non-food and non-drug containers. Laser energy heats a very small area of the composite Water-based release agent specimen. The resulting thermal expansion between fibre and resin causes debonding to occur, which A new water-based, environmentally-safe release agent produces a measurable acoustical emission. In general, is said to replace solvent-based formulations used to the stronger the interfacial bond, the weaker the release thermoset resins from a variety of tooling acoustical signal. surfaces. Based on a blend of silicone resins and oils in a water emulsion, Aqualease 6102 from George Mann For most composites, the reinforcement and matrix and Co., Proidence, Rhode Island, exhibits improved materials have different coefficients of thermal expan corrosion resistance, and contains no hazardous solvents. sion. As a result, heating or cooling can cause debonding It is suggested for use with urethane elastomers, at the interface due to the build-up of thermally induced epoxies, polyesters, and vinyl esters, to provide excellent stress. release and better film formation than previous water- The new method also can be used to monitor the based products. Best used wit h hot moulds (150°F and interply strength. In a PMC, all the fibres withi n a ply are above), this material mixes easily with water to form a oriented in the same direction. This orientation direction release agent ready to use on aluminium, steel, epoxy changes only between plies. For a given ply, a thermal and urethane mould surfaces. expansion occurs mainly at directions perpendicular to the fibres. What results is a mismatch in the direction of preferred thermal expansion between plies, which can induce large interply thermal stresses and lead to failure. Silicon based polymer binders Scientists at Southwest Research Institute, San Antonio, Debonding events in both instances are monitored by Texas, reportedly have developed silicon-based polymer an acoustic-emission detector. Instead of measuring the binders that can be used to make tough, heat-resistance thermal stress, which depends on the local temperature ceramics. and local temperature gradients, the laser-power level at The organometallic polysilazanes have a complex, which debonding occurs is taken as an index of the three-dimensional structure consisting of an inorganic debonding stress. backbone with organic appendages. When a ceramic The detected debonding emission signal (or signals) containing a new binder is fired, the polymer decomposes can be correlated to thermal-power levels in a number of to form silicon-nitride (Si N ) "whiskers," which toughen ways, including amplitude of the emission signal, 3 4 the overall structure. acoustic-event counts, total acoustic energy, rise time, The U.S. Air Force Office of Scientific Research is and duration. In examples shown here, the area under currently funding a programme to study the relationship the acoustic-signal curve (the total acoustic energy) is between the preceramic polymer's 3-D structure and plotted vs laser power to reveal information about the that of the derived ceramic. fibre/matrix interfacial strength of graphite-reinforced Other so-called preceramic polymers are commercially epoxy and polyphenylene sulphide. available, but they yield only a small amount of ceramic: typically less than 50 wt%. The new polysilazanes, High performance resin however, have a conversion rate greater than 90 per Solvay Polymers Inc. and Chemtrusion Inc. have formed cent. These high yields mean that the firing operation a partnership to produce a new high-density polyethylene has little effect on the part's shape and size. As a result, called "Fortiflex" XF855. The resin has a 25 per cent complex-shape parts such as turbine blades become content of recycled plastics including ground milk, water candidates for injection moulding. The polymers also and juice bottles. can be produced as low-viscosity liquids, which can be The work between the two companies started with used to make fibre-reinforced ceramics and ceramic small run development trials and feasibility studies. coatings. Solvay chose Chemtrusion, a small company with a
Pigment & Resin Technology – Emerald Publishing
Published: Nov 1, 1991
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