Dear Readers,

Weiboold Academy LogoThis is the first article from our new monthly blog series, called “Weibold! Academy”. The idea behind these articles is to provide our readers and our newsletter subscribers with valuable knowledge about the tire recycling industry.

We start our educational series with the basics and month by month we will together dwell deeper into the world of tires and the ways of recycling them. We believe that a good knowledge foundation might be beneficial for everyone involved in the industry and each month we will cover together different topics, thus providing you with important know-how for the tire recycling industry.

Here is the first article of our new series:

Introduction on the Characteristics of the Recycled Rubber Material

What’s Inside a Tire

Weibold! Academy pic.1TREAD:
Provides traction and cornering grip

Stabilize and strengthen the tread

Protects the side of the tire from road and curb damage

Gives the tire strength and flexibility



Assures an air-tight fit with the wheel

Keeps air inside the tire

Modern tire technology blends a unique mix of chemistry, physics and engineering to give consumers a high degree of comfort, performance, efficiency, reliability and safety. Many tires are custom-designed to meet the stresses and performance needs specified by the maker of a particular model vehicle. Every tire is carefully inspected, and random samples are pulled for additional safety tests. As part of these tests, tires are x-rayed, cut apart and examined, run on test wheels, or road-tested to evaluate handling, mileage and traction performance. If properly cared for, tires can last a long time – usually from 40,000 to 80,000 miles, depending on the application. (Rubber Manufacturers Association)

The raw materials in tires include natural and synthetic rubber, carbon black, nylon, polyester and even Kevlar cord, sulphur, oils and resins, and other chemicals. These constituents form various parts of the structure of the tire, giving it strength whilst retaining sufficient flexibility to ensure that adequate road holding properties are maintained under all conditions.

The following are the average ingredients of a raw mixture:

  • Rubber: 40-60% NR, BR, SBR, NBR, IR, EPDM Responsible for basic rubber properties
  • Filler: 20-50% Carbon black of different activity, chalk, silica, Kaolin etc. Strengtheners, extender
  • Plasticiser: 1-20% Mineralicoils, aromatic and aliphatic esters, tar, polymer plasticiser Improved process ability and filler in corporation, improved flow ability of the raw mixture, rubber properties(modulus, hardness, flexibility)
  • Additives: 5-10% Crosslinkingagents, activators, accelerators, delayers, stabilisers, processing aids Influence on cross linking, protection against ageing, improved process ability.
Weibold! Academy pic.2

The vulcanization process during tire manufacturing involves reaction with sulphur that is ordinarily irreversible, making it virtually impossible for a tire to be broken down naturally to its original raw material state. Disposing of tires in an environmentally sensitive and economically viable way therefore presents major challenges. With tires, the reduce, reuse and recycle theory is not so easy to implement because of their complex nature, their durability, their varying sizes, the numbers involved and the wide geographical distribution.

Theoretically it is possible to recover oil and carbon black from tires using intense heat (e.g. pyrolysis process) but due to generally low-value quality of the output materials only very few plants of any reasonable size employing this method are in operation today. Many companies have been claiming to have solved the problems but usually lack to show industrial scale references.

Tires have a high energy value and can be utilized for the generation of electrical power and heat as Tire Derived Fuel (TDF), however, due to the chemical makeup of tires there is an inherent potential problem of atmospheric pollution. High quality filtration technology is required.

According to the United Nations Basel Convention, Identification and Management of Used tires (1998) and the European standard, CWA 14243 (2002), post-consumer tire materials and representative applications, post-consumer tires are neither a dangerous nor a hazardous material when properly treated, transported and stored. Most of the rubber used today in tire manufacturing is petroleum based synthetic rubber. A new passenger car tire contains the equivalent of +30 liters of oil while an average new truck tire requires an equivalent of +93 liters. Despite a period of falling petroleum prices there is a need for greater conservation and increased efforts to valorize the valuable resources in commercially viable, cost-effective, environmentally sound ways.

Many of the characteristics that are beneficial during their on-road life are equally advantageous when post-consumer tires are used as raw materials in applications and products. In any form, a tire retains its inherent characteristics including retarded bacteria development, resistance to mildew and mold, heat and humidity, sunlight or ultra-violet rays as well as to oils, many solvents, acids and other chemicals.

The physical characteristics of tires are also an asset as they are non-toxic, non-biodegradable; their shape, weight and elasticity make them candidates for a range of applications in whole, cut, granulated or powdered form.

During the past 20 years the variety of materials produced from post-consumer tires has expanded particularly at the extremes of the spectrum:

Civil engineers are using greater quantities of larger materials i.e., whole tires, shred and chips for such applications as sound barriers, insulation, lightweight fill, bridge abutments, among others, and have fostered the development of new uses in landfill engineering and environmental rehabilitation.

Product manufacturers are using smaller materials produced from new technologies and material blends for such products as automotive parts, sealants, coatings, pigments, as well as a range of new road surfacing and treatment materials.