HSM Origins

A New Technology With a Long History

In the 1950's, Dr William F. Watson and co-workers showed that under certain conditions uncured rubber could be softened purely by mastication.

Although this phenomenon had been observed by others, Dr Watson was able to develop a theoretical treatment of this effect, backed by experimental result. The theoretical treatment was based on mechanochemistry theory in which predictable changes to the chemical nature of a material can be achieved by applying mechanical forces.  

The principle of altering the molecular weight of a polymer through mastication is now an established technique in the rubber industry. It is reasoned that the the softening of rubber is the result of the rupturing of main-chain bonds caused by the extension of the central sections of the rubber chains.

During the last 20 years, Dr. Watson has extended this theory to cured networks, examining both sulphur and non sulphur cure systems.

As an example, for a sulphur bonded system examination of the bond strengths indicates that under certain conditions, the sulphur bonds are weaker than the carbon-carbon bonds. The bonds within the crosslink should therefore break before the carbon backbone. It can therefore be reasoned that if stress is correctly applied across the total network, then the crosslinks should break preferentially.

A number of experiments were carried out by Dr Watson in the 1980's and 1990's to verify this effect. Further work has been carried out by Watson Brown and others since 1998 on a wide range of materials and at scales up to production quantities.  

This work has shown that most materials processed in this manner can be treated as compounds that can, with the addition of a suitable cure package, be recured, or can be added to virgin stock often at percentages equal to the scrap rate within a factory.     

Whilst arguably not exactly the same as the original material, hsm processed materials can often be reformulated to perform within 10% of the original material specification. In some instances, typically resistance to shear, hsm processed materials often outperform the original material specification.

Similar results can be achieved using other curing systems, such as peroxides and bisphenols.  To achieve this effect, the temperature and the nature of the applied stress fields are critical. The ruptured bond ends are free radicals. Normally these free ends are terminated by combining with oxygen. They could be arranged to react otherwise, such as combining in pairs in the absence of oxygen, reacting with an added small-molecule radical acceptor, adding to the surface of a reinforcing filler or initiating free-radical chain reactions. 

The process is simple, does not rely on any added ingredients and can be applied to a wide range of materials and formulations.

Recent developments

A 2 kg machine and later a 20 kg production unit have been developed to perform and validate the theory on laboratory and production samples.

Since the takeover of Watson&Brown in 2013, REP have industrialized this equipment.

The REP made production unit and the 2 l machine (designed for lab samples and thus preliminary testing) are available since 2015.

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