Synthetic rubber may gain in use with new process


The grating sound of worn-out wiper blades scraping across wet windshields may be a bygone irritation if a University of Maryland researcher can perfect a rubber that resists damage from ozone exposure the way its fans think it will.

The United States entered the rubber-making business under a cloud of war. The Japanese invasion of the Malayan Peninsula with all its rubber trees in the early weeks of World War II produced a rubber scare in the United States, driving American chemists to cook up synthetic rubber from a mix of coal and oil.

The synthetic rubber industry survived, but current-generation products commonly wear out faster than the natural product, usually because of three factors -- friction, heat and ozone degradation or "dry rot."

Now, by using the energy of electrons to cure the material, Dr. Joseph Silverman, a University of Maryland College Park scientist, believes he has developed a synthetic rubber that is tougher and longer-lasting.

"It resists abrasion and ordinary degradation much better than ordinary SBR [styrene butadiene rubber], which is the cheapest and most common kind of synthetic rubber," said Charles H. Church, director of advanced concepts in technology assessment for the U.S. Army, which funded the research.

The electron-beam process that Dr. Silverman and his engineering colleague, Dr. Walter Chappas, use to cure the material "offers revolutionary potential," said Michael E. Montie, a nuclear engineer with General Dynamics Corp., a Virginia-based defense contractor for tanks, cruise missiles and submarines.

Until now, the process has been used for plastic pouches for packaging turkeys and for curing plastic-coated wiring to make it less likely to burn. What's new, Mr. Montie said, is applying the technique "to create new materials with properties that cannot now be made." For example, the process makes common synthetic rubber resist dry rot, he said.

Dry rot causes windshield wiper blades to wear out and tires to crack by degrading the rubber from the outside in.

The electron-beam technology also will allow scientists "to create advanced composite material, such as plastics, that have characteristics and strengths they did not have before," Mr. Montie said.

Proponents of the University of Maryland technology said the new process should cost less in energy and labor than using heat to bond together layers of fibers, and it may add to the durability of products.

Before rubber is cured, it has the consistency of "a very viscous dough," Dr. Silverman explained. The dough is actually made up of many strings of rubber that are somewhat like "freshly cooked slippery spaghetti," said Dave Kerluke, a businessman who has contracted with the Canadian military to use the UM technology.

Curing the rubber gives it form and durability, because it links adjacent chains of molecules somewhat like spaghetti that sits, gets cold and sticks together in some places, Mr. Kerluke said.

In developing his curing process, Dr. Silverman, a professor of materials and nuclear engineering, added less sulfur than is used in heat curing and partially cured the rubber with heat and pressure. Then he bombarded it with millions of volts of electron energy from a $1.5 million electron accelerator in his laboratory.

Just one blast from the accelerator is equivalent to 10 lethal doses. The 9-foot-long accelerator is behind a thick concrete wall and steel door for the safety of human operators in an adjacent control room.

Use of the electron energy allows Dr. Silverman to link the rubber molecules at low temperatures with little or no sulfur. The scientist said he thinks that is why "my rubber resists use and abuse at higher temperatures much better."

The first application of Dr. Silverman's super rubber has been on tank tread pads, which wear out and cost the Army $100 million a year to replace. Dr. Silverman said the pads proved to be "far superior" to regular synthetic rubber pads on pavement, but not on gravel and rough terrain. Army testers said the pad started separating from the back plate of the treads, and they don't plan to use it.

However, Atomic Energy of Canada Ltd. in Ottawa made 700 tank tread pads of rubber cured with the University of Maryland process during the latter half of 1990, and 600 Canadian tanks will be fitted with them, said Mr. Kerluke, the company's market development manager. Another 100 pads will be tested on a specially constructed area that includes pavement and rough terrain.

In six months, Mr. Kerluke said, results should be in on whether the UM researchers' rubber lasts longer than conventional synthetic rubber or the rubber from trees.

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