Grafting more for less with reactive olefin prepolymers

Most people would agree that a winning lottery ticket would be sadly underutilized as only a bookmark.

In much the same way, plastics processors who use reactive olefin prepolymers (ROPs) as either additives or coupling agents may be short-changing themselves. But this may change if Dr. David K. Potter and Clariant (Canada) Inc. have their way.

Best understood as low weight polypropylene (PP) or polyethylene (PE) prepolymers with some reactive capability, ROPs are manufactured by numerous chemical suppliers, including Clariant, which sells them under the brand name Licocene.

Potter, a member of the department of chemical engineering at McMaster University in Hamilton, Ont., has been working with Clariant for the past six months to develop a means of helping processors manufacture cheaper, more flexible and more customized parts by improving polymer functionality through ROPs. The project is being assisted by the Ontario Centres of Excellence, a research support group.

“Traditionally, processors have added functionality to polymers by processing high viscosity and high melting point commodity resins like PE and PP together in an extruder,” Potter said. “During the extrusion process, the functional group would be attached, or grafted, onto the polymer.”

But there have always been problems to this approach, Potter noted. “First, the residence time in the extruder was limited, which meant that the amount of functionality added to the polymer was limited also, typically in the range of one per cent,” he explained. Second, he continued, the extruders tended to be big, bulky machines with large footprints. “In addition to taking up floor space, this could make it difficult to process polymers in locations close to customers,” Potter said. Third, the extruders often required expensive molds designed towards making the same volumes over and over again, which worked against flexible manufacturing.

Potter and Clariant believe that ROPs offer several advantages as a reactive agent. “Because of their low viscosity and low elasticity, ROPs can be processed in low temperature batch reactors rather than extruders, meaning that you don’t have the residence time limitations and therefore can attach a lot more functionality to the polymer,” Potter said.

Removing the extruder from the equation also makes the process cheaper and simpler, he continued. “Processors will no longer need costly molds and high clamping pressures,” he explained. “This also allows for the very cheap manufacture of articles in small volumes, and movement of the point of processing closer to the customer — right into his factory or construction site in some cases.”

The ultimate goal of using ROPs as processing agents is to facilitate what Potter described as the trend away from mass production and towards mass customization in the North American plastics industry, an idea outlined in a recent Plastics Technology Study released by the Canadian Plastics Industry Association (CPIA).

“ROPs are a step towards achieving mass customization, by making unique products for unique customers through processes that are very adaptable and materials that can be tailored with specific properties,” he said. “All the ways in which people are using grafted material right now are candidates for this approach.”

Clariant (Canada) Inc. — Pigments & Additives Division (Markham, Ont.);www.pa.clariant.com; 905-479-4700 Ontario Centres of Excellence (Toronto); www.oce-ontario.org; 416-759-6014