Editor's note: Mike Sepe is technical director at Dickten & Masch Mfg., a molder of thermoset and thermoplastic materials in Nashotah, WI. He has provided analytical services to material suppliers, molders, and end users for more than 15 years and writes a bimonthly column for IMM called the The Materials Analyst.
The history of civilization can be told through the development of materials. In fact, the early eras of history bear the names of the materials that were dominant at that time such as Stone Age and Bronze Age. As the fabrication process for each new family of materials came under the control of the appropriate processes, lessons were learned about their unique characteristics and the associated design and performance.
More importantly, control over new materials often brought control over the surrounding world. Those who have read the history of early civilization know that the first cultures that gained a facility in working with iron quickly asserted military if not cultural superiority over those who continued to work with bronze.
More recently, the development of polyethylene in the late 1930s and its initial commercial production in the early 1940s are identified by many as key factors in the outcome of World War II. Prior to that time, the insulation used to shield the wire carrying essential communications and radar transmissions was made of rubber materials that quickly cracked and broke down in outdoor environments. Polyethylene cable sheathing had a longer mean time to failure and provided the Allies with an important strategic advantage and an early example of Information Age superiority. The case can be made that over the course of the war, polyethylene saved more lives of Western forces than uranium did.
Within each era defined by a certain material family, there are watershed moments, events that extend a technology that appears to have reached its limits. The development of phenol-formaldehyde resins by Baekland in the first decade of the 20th century, the creation of nylon and polyester fibers at DuPont in the 1920s and '30s, and the development of Ziegler-Natta catalysts that extended the range of polyethylene properties and turned polypropylene from an adhesive into a useful polymer in the 1950s are such events in the world of plastics. At each turn a creative world seized on the new opportunities offered by the revolutionary materials to manufacture products that were previously unimaginable.
Today the plastics industry is on the verge of a new revolution in materials development. Rumblings of this revolution have been in the background since the mid-1990s and the people close to the fundamental research can probably trace the active work back to the late 1980s. It is a revolution driven again by catalysts. Ironically, these materials are not new; they were known in the 1950s but were thought to be impractical because of their low efficiency. Over an extended period of time, serendipitous discoveries have moved these materials from laboratory curiosities to materials that can drive chemical reactions on a scale required for commercial practicality. As a family, they go by the name metallocene, a chemical term that describes the general chemical structure of these materials.
A New Level of Control
To understand what these catalysts mean to the business of material creation, you must first understand some of the shortcomings of the current technologies. These are shortcomings we have learned to live with, so we may not see them as such, but the reality is that polymerization, like most organic chemistry, has always been a game of probabilities. When a grade of conventional polyethylene or polypropylene is produced, the range of molecular sizes that make up the material may be quite broad. The low molecular weight fraction in such a distribution facilitates flow during processing.
However, it also contributes to reduced impact properties and may be the cause of volatilization that promotes plateout on mold surfaces and produces taste and odor problems in some applications. The presence of a small number of very large chains helps to counter the negative effects of the low molecular weight fraction. But if these become too large they can form gels. These are portions of the polymer matrix that do not soften and flow even though they are heated above their melting point. These are particularly troublesome for thin-walled products. The new catalyst systems allow for the creation of grades where both the low and high molecular weight extremes can be eliminated while still producing the desired properties.
The new level of control can also be exercised over composition. For example, commercial polypropylene is primarily made up of a material that has an isotactic structure. This means that the pendant methyl group in the polypropylene repeating unit appears in the same location throughout the chain. In conventional materials the reality is that something like 80 to 85 percent of the repeating units in the individual chains exhibit this regularity. The other 15 to 20 percent may not be so accommodating, and the strength, stiffness, and heat resistance of the material is reduced to the extent that this structural regularity is lost. These unstructured or atactic groups are not without their uses; they promote melting and flow of the polymer and can improve impact resistance, particularly at low temperatures. But their placement within the individual molecules is irregular and random.
The new catalysts change all that. Structural order can literally be controlled one unit at a time, providing unprecedented control over performance. In the past, the shortcomings produced by the randomness of polymer structure were corrected by the addition of other ingredients. Now the alteration can be accomplished within the molecule. It is a good rule of thumb that any modification made to the inherent structure of a polymer produces a better result in terms of a particular property improvement than if the same change is accomplished with the addition of a second ingredient.
Opening New Doors
Let's review a partial list of the developments made possible by the new catalysts. Polyethylenes can now be made to lower densities and with more predictable property profiles. A polyethylene with controlled side branch placement can produce the same combination of properties that could previously only be achieved with copolymers such as EVA and EEA. In EVA the material becomes softer and more pliable as the vinyl acetate content increases. More vinyl acetate means less thermal stability in the melt and higher density.
The new soft polyethylenes achieve the same properties without these sacrifices. It is now possible to produce polypropylenes that employ varying levels of isotactic, syndiotactic, and atactic structure within each polypropylene chain. This allows for an incredible degree of control over crystallinity and all of the properties that arise from it: strength, stiffness, impact resistance, heat resistance, and melting point, to name a few.
Of course, the advances go beyond the commodity level. New copolymers of ethylene and norbornene, known as cyclic olefin copolymers, are transparent, have thermal and physical properties that can compete with polycarbonate at a much lower density, do not absorb water, and resist polar solvents. Adjusting the comonomer levels moves the glass transition temperature from as low as 80C to as high as 180C, and it can go higher if needed.
Polystyrene can now be made with a semicrystalline structure. The resulting material, with glass reinforcement, has a property profile that competes with thermoplastic polyesters, nylons, and even PPS. It exhibits lower melt viscosity than any of these materials, has excellent electrical properties, and does not absorb moisture. Therefore, no drying is required prior to processing and no degradation can occur due to the presence of moisture either during processing or in field use. These syndiotactic polystyrenes also exhibit less warpage than competitive materials and have densities at the same glass loading that are 10 to 20 percent lower than the traditional engineering materials.
With such advances already accomplished and a host of others possible, it would seem natural that these discoveries would be changing the face of the industry, enabling the creation of new products the way new polymer developments have in the past. But for the most part the response from the marketplace has been less than overwhelming. In groups that I address on a regular basis regarding new materials technology, fewer than 5 percent have even heard of most of these developments and far fewer have sampled or implemented them. So what's the problem?
There are two problems, actually. One is the mania over cost reduction or, more precisely, price reduction. If cost reduction were really the focus, a reasoned approach to the manufacturing process would suggest that turning off the dryer, reducing part weight by 15 percent, eliminating or reducing warpage, and cutting cycle time and pressure required for moldfilling would translate to a cost reduction. But qualifying new materials takes a little workâan investment of time, energy, and thought to determine where the best opportunities might lie. Many engineering staffs at OEMs are so decimated by the reengineering craze of the 1990s that there is no one left to work with the processors on such projects. This assumes, of course, that molders are scouting the landscape for such creative solutions in the first place.
The alternative to such an innovative, value-added approach to cost reduction (and, unfortunately, the approach that tends to prevail in most markets) is to simply beat down the supplier of the current material for another 5 percent reduction in cost per pound or seek out a secondary supplier who can compound a reasonable facsimile of the material currently in use. So while researchers work on new polymers that incorporate all the many advantages of unprecedented control over structure and composition, molders and end users are sourcing the next generation in cheap materials.
These materials are based on streams of material that are set aside by the major manufacturers as "wide spec" or they are blends of different materials designed to achieve a particular short-term property profile. When the products made from these materials fail, as they often do after the first two or three successful lots, the cost to pick up the pieces is always much higher than the initial savings. But the pressure of short-term thinking is obviously more than most processors can withstand, and so price cutting replaces innovation as the preferred development path.
The second problem lies with the developers of the materials themselves. Innovation is seldom a welcome thing. Tom Peters jokes about the reception that the person who invented the wheel, a guy he calls George, probably got from his neighbors when he first started to roll it around. The usefulness of the device was probably not immediately obvious when there was only one prototype available. But even when the utility of the invention became apparent, Peters imagines the rest of the community saying, "Look at George, real men carry rocks on their back." In other words, really innovative ideas do not immediately take over the marketplace because the usefulness of the idea has to be articulated by the creator and strengthened by application to things that might not even have been manufacturable before. The inventors of the new polymers have been missing in action in fulfilling this role.
More Than Just a Data Sheet
Part of the reason for this is that the primary means of communicating property information about plastic materials comes in the form of a short-term property sheet, a table of single-point values documenting points of catastrophic failure on specimens of uniform nominal wall that are free of weldlines and employ optimal levels of orientation. With the exception of the heat deflection temperature, which is not a property at all, the measurements are all made at room temperature.
The uselessness of this information is becoming institutionalized in our information age. Material suppliers have always made use of the disclaimer in fine print at the end of these documents, but recently some major suppliers have begun to display the disclaimer prominently in the introduction to the data sheet section of their websites.
At least one supplier brings up the disclaimer in a pop-up window that requires the user to read the verbage disavowing any relationship of the numbers to real-world performance. In order for users to gain access to the data sheets, they must not only read the disclaimer but also must click on an "Agree" icon provided at the bottom. If the user doesn't agree, access will not be granted to the data sheets. In other words, before we let you see our property information you have to agree that it's meaningless. This is tacit admission of the futility associated with generating these numbers in the first place.
In spite of this "emperor has no clothes" scenario, there is very little information provided about materials outside the realm of the data sheet. This is particularly true at the commodity level and very unfortunate for the new technology materials, because their real value does not come through in the data sheets.
There is no way to capture the advantages of a narrow-molecular-weight-distribution HDPE or a cyclic olefin copolymer by resorting to the old, tired formula of tensile strength, flexural modulus, HDT, and notched Izod impact. It requires an intelligent discussion of physical, electrical, and chemical resistance properties as a function of temperature, time, and load. No one doing a cursory search of a large material database is likely to be drawn to these materials by the types of numbers that we tend to use for "performance" assessment.
The second problem that the material suppliers have is that they bought into the "price is everything" philosophy. With billions invested in new technology, they seem unable to leverage the strategic advantage of innovation. Instead, they either try in vain to compete with the second- and third-level compounders on price, or they mothball the technology and pronounce it unmarketable in today's competitive climate.
Going Against History
At risk in all of this is a series of developments in polymer technology that could revolutionize the way materials are made and sold, improve old products, and enable new products. It may mark the first time in recorded history that we have consciously eschewed new breakthrough technology in favor of supposed cost advantage.
Of course, history teaches that there is no winning in turning away from the practice of doing things better. The cultures that mastered the new technologies of advanced materials won the wars and spread their cultures in favor of those that would not or could not change. Imagine in retrospect how ludicrous it would be to have a buyer pass on the new iron tools of 700 BC because the raw material was more expensive or a new furnace that runs at higher temperatures might be required to process it. Or the designer who decided to stay with the old rubber insulation for radar cables in 1941 because the new polyethylene was too costly and required a strange, new machine to coat the wire.
There have been times in history when the lure of high-volume production and the availability of discretionary spending have prodded manufacturers into cheapening their products for short-term gain. By the time the Roman Empire reached its heights it had produced something unique in the ancient world: a substantial middle class. This middle class had extra money to spend, and one of the things that this money was spent on was marble statuary. Previously these statues had been the hallmark of the upper class and they were therefore prized by those with newfound prosperity.
This produced a large increase in demand for the sculptors who worked in the center of Rome's market district. The need for higher production rates meant that products that would normally be too low in quality to sell could be doctored and salvaged for sale to the less discerning middle-class newcomers. Rather than scrapping a statue or working for long hours to repair damaged surfaces, the imperfections in the marble were filled with wax. The wax matched the color of the marble and looked good, but when the statues stood in the hot sun, the wax melted and the imperfections became obvious. Some of the sculptors, rather than surrender to the low-end tactics, distinguished their work by putting signs up in their work areas that read "sin ceres," or, without wax. This phrase is the origin of our word sincere.
The notion of sincerity in materials and manufacturing may seem like soft stuff. But without a commitment to better ways of doing things, there can be little improvement in technology. Materials are a key element of this dynamic. Part of the genius of the early days of the DuPont and General Electric polymer laboratories was that no one knew exactly what the product of their work would be. But the drive for innovation and the need to provide solutions to real-world problems brought forth some of the product names that are the icons of our industry today.
Without innovation, competition devolves into a reliance on the ineptitude of the competition. This is not a sustainable advantage. Metallocenes are the breakthrough of this time; there will be others. Here's hoping that the innovative process will be revived and that the integrity of a company's products still means at least as much as the price of a company's stock. Otherwise, the story of the plastics industry in the 21st century may parallel the story of the steel industry of the 20th century.
Dickten & Masch Mfg. Co.
(262) 369-5555, ext. 572