As a veteran of the polylactic acid market invasion (PLA or polylactide) in the late 1990’s, I was heartened to see a new commodity application of PLA packaging appear on the shelves of the hometown grocer.  Well, alright. MArket invasion is overstating it a bit. We were one company among several in the race to grab PLA market share.  The founders of our company were engineers familiar with corn wet milling and the starch business. In the end, the skill set that carried the day was the combination of Cargill’s agribusiness presence and Dow’s massive polymer production business expertise. We were doomed. Our place as a Coors subsidiary with a modest cornstarch and wet mill operation just didn’t give us the gravitas to make the thing happen.

PLA is the polyester of lactic acid monomer, or perhaps more accurately, lactide monomer.  I’m generally in favor of PLA as a replacement polymer for polyolefin materials. PLA ultimately sources from starch fermentation in corn steep liquor.  Our process produced lactic acid using steepliquors as a nutrient source. 

One of the reasons I left academics was the unusual chance to be part of a seemingly well funded startup aiming to commercialize a PLA process.  I’ve written about this before and won’t repeat it here. Our operation ultimately shut down within a year of my arrival due to some technology problems and a nervous group of investors- not an uncommon scenario.

My job was to come up with a comonomer for PLA to raise the glass transition temperature (Tg) and to bring down the crystallinity a bit. But first, some background.

One of the issues with PLA as a substitute commodity polymer was its relatively low Tg. PLA’s low Tg caused it to be unsuitable for contact with hot liquids.  Food contact applications are a major commodity market for polymer producers, especially if the value proposition to the consumer is the biodegradability of the product.  Commonly disposable items like coffee and soft drink cups & lids, plastic utensils, straws, and diaper components are cited as ideal applications for green polymers. In order for PLA to be substituted into the disposables market, the matter of price and performance had to be resolved.

Our projections by 1998 were that PLA would be price comparable with nylon, then roughly $1.50 / lb.  Nylon was more expensive than polyolefins/polystyrene by quite a range, so the thinking was that at least initially, PLA would be specialty polymer product selling along the applications margins. PLA would have to grow, gaining acceptance by some kind of consumer.

But what is “some kind of consumer”?  It is easy to fall into the thinking that the crucial polymer consumers are the people buying the finished goods containing the polymer. But that isn’t exactly true. There is another key group of buyers than must be satisfied. And they are tough customers.

A crucial group of people who make buying decisions are actually found upstream of the floor level consumers. They are the raw material buyers and they reside at several links on the value chain.

Let’s assume that the producer of a polymer -sold in pellet form- has produced a satisfactory product. It meets rigid specs for quality and performance.  The direct buyer of pelletized raw polymer is some kind of converter. A converter is a company that buys pelletized polymer and converts it to some variety of higher value product by the process of compounding and extrusion.  The compounder may produce films, filaments, or molded widgets. At this stage, polymer products are referred to as resins.

A compounder may be a producer of resin films or resin widgets who, in turn, supplies another manufacturer who uses the resin products for their own applications. Or, compounding may be integrated into the total manufacturing chain by one operator. A producer of things-that-contain-resin-widgets-or-films may have their own extrusion operation to contain cost.

What is critical to anyone scheming to bring a new polymer into the market is this: you have to sell the new resin to the compounder. If the new resin is more expensive, then the value proposition just got really difficult. A new (replacement) resin must have some kind of added value to the compounder and for the manufacturer downstream to  justify the disruption that its substitution is likely to cause.

What kind of disruption can polymer substitution cause?  All manufactured goods have specifications by which the manufacturer is able to distinguish acceptable from unacceptable quality. Specifications for components usually cite raw material specifications comprising physical or chemical properties, appearance, odor, or even specific commercial brands.  Swapping materials of construction or different compositions is a serious undertaking for a manufacturer of established goods. If it ain’t broke, don’t fix it.

So, a resin substitution may require the persuasion of decision makers in a multicompany value chain to effect a substitution. This is the challenge before any producer of new resins. And PLA was in the same place as it was going to market in the late 1990’s. It takes a giant company with massive resources to effect the adoption of a new resin in the marketplace. Sales efforts have to be focused on the true decision makers. These are the manufacturers of packaging materials and the industrial buyers of resin components. They have to be convinced that any new resin won’t hurt existing sales and that there be some kind of premium for going to the trouble adopting change.

So, the new bag containing Frito-Lay Sunchips is on the market and it is made of PLA. Somewhere along the line a decision has been made to risk the change. I’ll say that the bags seem to have the same appearance as the previous variety.

The only problem is the rattle. The bags have rather a loud rattle due to the considerable crystallinity of PLA.  The way to make the rattle go away is to coploymerize it with a comonomer that increases the amorphous nature of the polymer. PLA is made from enantiomerically enriched, biologically derived L-lactic acid. L-Lactic acid is used because it can be made cheaply by fermentation. The bugs only make one enantiomer.

The challenges of successfully incorporating a comonomer are many, and they are not all science related either. A comonomer must participate in ring-opening polymerization and combine with lactide. The relative reaction rates need to be in a range that allows for favorable incorporation without undue increases in reactor residence time. Comonomers can produce compositions varying from blocks of comonomer incorporation to random incorporation. It takes a lot of time and resources to work out the most desirable compositions and their respective economics.  

We were using reactive extrusion where the residence time was related to screw speed and length of the extruder. Too much residence time at reaction temperature and the PLA would carmelize or darken. Residual acid is a killer. PLA is very sensitive to residual acid in the lactide. Very small amounts can be ruinous. It shut us down.

Incorporation of a comonomer that is not an agricultural or renewable product will taint the value proposition of “Green”.  Caprolactone is an example of a comonomer that had been explored by others, but I’m not presently aware that there is a Green route to that monomer. I recall that there were patent issues that prevented us from exploring caprolactone. However, there is a good chance that the patent issues have now expired. Nothing is forever, not even patents.

Follow this link for an earlier post on this topic.

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