Last year we carried a mini-series on additives. This covered such materials as rubber pieces, PVC wire insulation, carpet scrap and nonwoven felt. We also stressed the importance of fibres in providing cohesion, hence shear strength to a surface, and also contributing to shock absorption. Because of their significant importance, this month we dedicate a complete Footing Facts to fibres. Fibres have been used for thousands of years. In fact the earliest use of fibres by man is thought to be around 34,000 years ago. The flax fibres could have been used to make clothing, but also in structural application such as rope and twine, and thread. These fibres of course were natural, and included cotton, jute, wool and silk. Such fibres have served man well for thousands of years, offering strength, warmth and comfort. They also, conveniently, biodegrade quickly.
However, deficiencies in natural fibres, and man’s quest for technological advancement saw the development of synthetic fibres in the 20th century. Synthetic fibres are built using chemistry by joining small molecules together into long chains – so-called polymers. These polymers, or plastics as we tend to call them are extruded through holes and the polymer is usually stretched to thin the strands down and make them stronger. The most widely used synthetic fibres today are polyester which is used mainly for clothing, polypropylene used mainly for carpets, and nylon which is used for clothing, carpets and industrial applications.
One key property that sets these synthetic fibres apart from natural fibres is their reaction to water – natural fibres tend to be attracted to water and therefore absorb it (hydrophilic), whilst synthetic fibres tend not to be so attracted to water and absorb much less (hydrophobic). Because synthetic fibres are less water-loving, they also biodegrade more slowly.
Synthetic fibres can be useful additives in equestrian footings. Because they biodegrade slowly they will not rot when left in wet sand. Natural fibres on the other hand can rot in an equestrian surface environment, and it causes us some alarm when we come across surface suppliers and installers who are selling natural fibres such as rayon as additives. Of the synthetic fibres, polyester is probably the ideal choice because it is not too water hating, nor too water loving. It is at home in a watered sand arena, and in a non-watered coated (wax or polymer) surface. On the other hand polypropylene, whilst ideal for a coated surface, is extremely hydrophobic (water hating) and not compatible with watered sand footings. However there are some well known suppliers out there in the industry who sell products containing polypropylene fibres for watered arenas.
The physical dimensions of the fibres is vitally important. The diameter, or thickness, known in the industry as denier is one characteristic. Cheaper fibres tend to be thicker, but these are not ideal as additives because they do not blend well with sand and easily separate and rise to the surface.
The caption shows the footing from an arena we visited recently where the arena manager was at his wits end trying to constantly re-mix the fibres back into the footing. We advised that the wrong size fibres had been used. The next caption shows one of his fibres next to an Attwood fibre under a microscope – although the image is not entirely clear it can be seen that our fibre is at least half the diameter. And it’s not just miscibility that suffers with large diameter fibres. These products are sold by weight, and incorporated by weight – a typical incorporation level might be 2%. If a fat fibre product is used, say 2x the diameter of a thinner product, and you buy 1000Kg, you will get only ¼ or 25% of the number of fibres that you would with the thinner product. If the fatter product was 3x as fat then you would only receive 1/9th or just over 10% the number of fibres. (Notice it’s a square relationship).
The length of the fibres is also important and we showed a graph last year of the effect of fibre length on the shear strength of Attwood’s polymer coated Pinnacle product.
Too short and the surface is too loose, too long and the surface is too stiff and can’t be harrowed.