Recipe for Better Recycled Tire Rubber Mat

Hello jgreg1

You don't give your Location or Country (easily done in your Member Profile and it auto-updates through all your Posts), thus general advice is given here.

When truck and car tyres were made years ago, they were always crossply, not the radials made these days.

The tyres were then hand-made, using a high proportion of natural rubber, no synthetic rubber.

The nylon addition was carefully measured also.

The proportion of Sulphur was greater.

The proportion of carbon added to the mix was greater than today.

Mixing was done in a "Bunbury Mixer" - see picture of the Bunbury mixing rollers here which kneaded the mixture until proper mixing was assured.

The early ply ratings were accurate, 10 ply being 10 actual cotton fabric plies, unlike these days where a 6 ply radial tyre may have only 2 actual plies.

The weave of the crossply tyre was diagonally cut, so the fabric ran in diagonals across the tread, from rim to rim.

The automatic crossply fabric cutter was designed right here in the Christchurch, New Zealand factory of Firestone, many years ago.

So the old car and truck tyres were thicker, stronger and lasted far longer than tyres do these days.

Of course, the tyres you are using may have been made in a Country which pretends to have proper Quality Assurance Controls in place, but does not really follow those procedures.

The resultant tyres are what you have: Thin, structurally weak with nylon fabric cords running parallel with the tyre circumference, less carbon black, less nylon, less natural rubber, less actual plies of fabric.

We use those rubber link mats here too, and I have noted that we in NZ have the same trouble as yourself.

It is not poor polymerisation, but insufficient Vulcanization which is part of the problem.

The old truck/bus crossply tyres took 2 hours 35 minutes cycle cure with partly wet steam for a typical 10.00" x 20" tyre, 2 hours 45 minute cycle for a typical 11.00" x 20" tyre.

The later thinner radial tyres are "cured" in a cycle around 45 - 50 minutes for the same size tyres.

So that's the reason the tyres just don't last: They are not made to last.

Here in Christchurch Firestone Factory all tyres used to have a serial number, made by the insertion into a slot in the mould of a pre-punched serial number, the serial numbers being consecutive, of course, and a record was made to check mileage obtained from a typical tyre.

It was discovered that small recipe alterations could enable a tyre to last well over 150,000 miles, but when Head Office was advised, the Christchurch factory was ordered to destroy the recipe details, as "We would only ever sell a set of tyres, perhaps two at most, to any car or truck.

The extra mileage was obtained by increasing the carbon black amount, then post-inflating to full pressure when the tyre was extracted from the mould, and immediately immersed in a cold water bath with the water being constantly replaced, until the tyre was cold.

This "fast cooling" altered the cross-linking obtained by the vulcanization process, the rubber being far stronger, although just as soft.

"Camelback" - The uncured rubber extrusion for retreads, was also made with the long-life recipe, with the same result after it was fixed to an old casing, and cured in a mould press, with the same post-inflation and fast cooling.

In those earlier days, it was common for a truck/bus tyre to be retreaded/recapped 10 or 12 times, car tyres 6 to 8 times too, a great saving.

What more can I say except that tyres these days are rarely recapped, except by the "Bandag" process, and often you will see a tread thrown from a modern recapped tyre - lethal if you are in the firing zone.

I trust that explains to you why the tyres and the consequent tyre mat materials just do crumble so easily these days in a "throw away" society.

Kind Regards....

Greetings from the former heartland of tire manufacturing in North America,Southern Ontario,specifically the golden horseshoe...Its amazing how tires/economic developement are related..I too had occassion to spend over a decade of my working for others for money in the rubber tire industry as a chemist..My thoughts on your problem(s) are multifaceted...First your binder system that is used to hold the pieces of recycled/already cured rubber may beinadequate to the task as you did say your proportion of car/truck tire recycled rubber has large variations...Secondly i suspect a much higher level of clays/silicas etc are in tires these days as its an excelllent way to save millions of dollars per large facility per year and still produce adequate(vs optimula easily obtainable)tires ..These increased loadings of inorganics only partially bound to the core polymers and at the microscopic level really only act as fillers of voids between entangled polymeric(organically linked)systems are likely a culprit in the breakdown of your product..At certain loading levels/with increased surface area exposed to frictional forces as in your mats the capacity of the fillers to act as tiny sandpaper to the surrounding matrix of softer polymers can not be overlooked..Add some virgin material to your mix with no added fillers and see if this does not improve your mat life ..Regards..Marty Wolf