We continue our multi-part series on plastic compounding with a posts about using cost comparison & temperature to choose the correct thermoplastic composite. So we don't have to recreate the wheel, RTP Company was nice enough to send over a white paper they put together that breaks the process down into five steps and this is step 2 of 5.
Cost Comparison & Temperature
Cost is an extremely important consideration when choosing the base resin from which you will build your composite. My experience has been that you can usually develop a composite to meet even the toughest physical requirements, but if it does not
meet the customer’s cost expectations, they will not buy it and your development efforts will be wasted!
Thermoplastic resins can be arranged into three basic categories based on their cost: low cost/commodity resins that typically have large volume market costs of less than $1.50/lb, medium cost/engineering resins that typically fall between $1.50-$3.00/lb, and the high cost/high temperature resins that usually cost above $3.00/lb.
If one compares the costs of all thermoplastic resins, they see a direct correlation between the cost and the temperature resistance of the resin.
Temperature resistance can be measured in a variety of ways: melt temperature, heat deflection temperature, glass transition temperature, and continuous use temperature; but the resins that will offer the highest capabilities in each of these categories will be the most expensive. For example, a couple of the top thermal performers
include Polyetheretherketone (PEEK) and Thermoplastic Polyimide (TPI) and both cost over $30.00/lb. This is why it is so important not to over-specify the thermal requirements of your application or you will needlessly drive up the cost
of the composite that can meet these requirements.
Although we usually discuss costs in the plastics industry in terms of $/lb, a thrifty part designer will always calculate costs in terms of the cost it
will require to produce a certain volume of parts:
$/in = $/lb X Specific Gravity X 0.0361
If you are ever outbid by a competitor in a situation where the competition has a higher specific gravity material, calculate the $/in3 and you may be surprised to find that you actually have the better price.
By combining the morphology, cost, and thermal requirements (as depicted in the following chart), one can see that you can quickly zero in on your choices to two or three resins that will best meet your application.