PLASTIC: THE UBIQUITOUS MATERIAL
Plastics have been an ever-growing part of our way of life – from the first synthetic plastic (Bakelite) developed by Belgian-born chemist Leo Hendrik Baekeland in 1907 , to Wallace H. Carothers’s discovery of nylon and the resulting nylon stockings rage of the 1940’s , to the Tupperware craze of the 1950’s, to metal replacement, to space age applications, and to the digital age. The rapid proliferation of plastics is not surprising because of their: (a) wide-spread availability of raw materials to produce it; (b) relatively low cost; (c) light weight; (d) excellent corrosion, chemical, and thermal resistance; and (e) good mechanical and physical properties. However, despite their excellent overall properties and benefits, plastics are not a panacea. They occasionally can and do fail in their intended service environment. Unfortunately, some of these failures wind up in litigation. When that occurs, I am often contacted by attorneys representing plaintiffs and defendants whose plastics have failed in service to act as an expert witness and determine why the plastic has failed.
Case Example 1. This case involved a 300-gallon plastic tank and valve holding concentrated acid. When the worker attempted to open the valve to transfer some of the acid to a process vessel, the valve completely broke off from the body of the tank, spraying acid onto most of the worker’s body. His burns were severe. I was retained to determine why the plastic valve broke. I carefully examined the broken valve visually, and then used x-ray radiography and a scanning electron microscope to generate high magnification images of the fracture surface. From those analyses, I found that the valve broke at the threads, and there were several very small cracks near the threads. I concluded that the valve failure was due to a combination of three factors: (a) stress cracking at the threads because the machined threads were an area of high stress concentration; (b) chemical attack of the plastic from the prolonged exposure (about 15 years) to the highly concentrated acid; and (c) fatigue cracking from in-plant vibration, and shipping of the container back and forth to the chemical supplier to be refilled over the 15-year period.
Case Example 2. This case involved the processing of a multi-layer plastic packaging film. The Plaintiff purchased a process and equipment that was reported by the supplier to provide a better product with a more cost effective and technically superior process than the industry standard process of packaging a very large-scale product. After spending millions of dollars on the equipment, and approximately two years trying unsuccessfully to get the purchased equipment and process to work effectively, the Plaintiff sued the supplier. The supplier claimed the Plaintiff did not follow the supplier’s recommendations or spend enough resources and time to get the new process to work properly.
I was retained to determine if the new process and product was feasible. Utilizing my expertise in polymer chemistry and engineering, I performed the following analyses: (a) heat transfer characterization of the plastic materials involved; (b) capability of the equipment provided by the supplier to sufficiently heat and cool the various plastic layers; (c) adhesion of the various plastic layers to each other; (d) ability to heat seal the package to achieve adequate package integrity and product shelf life; and (e) evaluation of the supplier’s methodology to scale-up the process and product from concept to feasibility to development to pilot plant scale to full production and commercialization using well-recognized industry methodologies. After thorough analyses, I concluded: (a) the process was not scale-able to economical large-scale production rates; (b) the product still needed major development work and improvements; (c) the supplier did not perform due diligence and introduced the product prematurely; and (d) the supplier materially misrepresented and overstated the technical capability, robustness, and production-readiness of the process and product.
TYPICAL REASONS FOR PLASTIC FAILURE
There are a myriad of reasons why plastics fail in service. The primary reasons, some of which are noted above, include poor material selection and design, improper processing, inadequate due diligence in developing the product and scaling it up to full production, plastic degradation due to exposure to severe outdoor environments and chemicals, thermal degradation from exposure to high temperatures, and mechanical failure from stress cracking, fatigue cracking, and inadequate strength or toughness. Plastic failure is usually due to a combination of the above factors, not a single root cause.
Many plastic material selection, melt processing, fabrication, design, and end-use environmental factors can and do contribute to why plastics fail in service. My background affords me the unique ability to piece those factors together to develop an unbiased, accurate understanding of why a plastic has failed in service.
ABOUT THE AUTHOR
Robert A. Iezzi, Ph.D., is founder of RAI Technical Solutions®, Inc. (www.rai-technical-solutions.com), a polymer technology company that provides expert witness and consulting services on plastics, paint and metal coatings, corrosion, and surface preparation/pretreatments for metals and plastics prior to painting.
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