Weibold! Academy: Recycled Rubber Output Spectrum and Rubber Granulates

Dear Readers,

Weiboold Academy LogoThis is the second article from our 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 started 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 different topics, thus providing you with important know-how for the tire recycling industry.

In the second article from our series we will start explaining about the recycled rubber output spectrum and we will cover the topic about Rubber Granulates.

Recycled Rubber Output Spectrum

An overview of the spectrum of granulation that can be achieved with various processes is as follows:

Weibold Academy Article 2 pic 1

The definition of the products and their corresponding grain sizes have been derived from Specification CWA 14243-2002 by the European Centre for Normalization (CEN) in association with the European Tire Recycling Association (ETRA).

Uncut tires and large piece shreds represent a liability (negative value) since it costs money to dispose of them. In many countries shreds are however used as fuel and will be paid for, but at a very low price. A business model based on selling tire-derived-fuel (TDF) relies on government funding for recyclers. Processing shreds further into smaller pieces opens up new markets and opportunities.

Recycled rubber is generally not a replacement for virgin or synthetic rubber, except for use in the manufacture of tires or compounds for products with similar properties. However due to historically low prices for virgin and natural rubber it is currently difficult to motivate the rubber industry using recycled material.

Rubber Granulate (European term)
Crumb Rubber (U.S. term)

The first step moving towards the reuse of scrap tires is to re-process (shred) them into small pieces with the fibers and metal removed, which is called rubber granulate. Rubber granulate can be used in a wide variety of rubber material applications. The industrial-scale based technology for re-processing scrap tires into rubber granulate started in the 1950’s and became mature in the 1990’s.

Over recent years the recycling industry has invested in modern technologies to improve the separation of the various tire components, in turn improving the quality and supply of rubber granulate. Rubber granulate has therefore become a more reliable raw material and this has given rise to the increasing number of manufacturers that are willing to explore the possibility of incorporating this material in their products.

Currently the biggest customers for consuming rubber granulate are sports pitch construction companies and molding companies. Other products that consume rubber granulate include solid wheels, floor mats, horse trails, playground surfaces, roofing materials and others.

In the following an overview about different types of granulates (differentiated by input material combinations and production methods):

Rubber granulates from car and truck tire input material

 

We estimate that more than 90 % of tire recycling companies are using a mix of car and truck tire input material.Weibold Academy Article 2 pic 2Table: Average material composition of car and truck tires (source: Aufbereitungs Technik 45 (2004) Nr. 5, A. Pehlken)

Main advantages:

  • Usually positive gate fee (especially for car tires)
  • Uniform availability worldwide
  • Relevant environmental requirements (e.g. DIN-V 18035-7) for main target industries fulfilled
  • Keeping its elastic properties also in cold climates
  • Extremely UV-resistant
  • Long lifetime (50+ years)

Main disadvantages:

  • Smelly in hot weather conditions
  • Sometimes textile contamination in sizes larger 2 mm

Rubber granulates originating from truck tires only

Truck tire rubbers contain an average synthetic rubber content of 15 % and an average natural rubber content of 30 %. There are only few tire recyclers who are specialized on 100 % input of truck tires. The availability of truck tires is much more difficult due to the following reasons: Many truck tires are retreaded and therefore have a much longer economic lifetime compared to car tires. As truck tires hardly contain any textile (except Russian truck tyres) it is highly demanded by tire recyclers. Generally gate fees are considerably lower compared to car tires. This is reflected in the market price for truck tire granulates and powders.

Rubber granulates originating from other tires or tire related materials

To complete the coverage, in the following you find an overview about rubber granulates originating from other tires or tire related materials:

  • Tires from airplanes, farming and earth-moving vehicles, etc.
  • Solid tires (e.g. forklift tires)

The above mentioned tires do not vary significantly from the average composition of car or truck tires in respect of its rubber composition. However usually these tires contain a higher natural rubber content compared to car tires. Tire from airplanes are difficult to recycle because of its very strong fiber belt (usually Kevlar fiber). We are not aware of any recycler treating airplane tires conventionally. Farming tires usually earn a good gate fee however the textile content is extremely high and without top-class cleaning equipment the resulting granulates and powders contain a lot of textile. Another side effect is a reduced processing rate. Tires from earth moving vehicles are extremely big and heavy and pre-cutting equipment is necessary to handle these tires. Gate fees are usually very high and it could be a lucrative alternative should the shredding and granulating equipment be capable of treating the chunky solid rubber pieces. Again there usually is a high natural rubber content and few textile which enables the recycler to target a premium market. Solid tires are difficult to treat and usually used as input material for rubber mulch production (mostly in the U.S. and the U.K.).

  • Buffings (German term: Raumehl; French term: fibrette) from tire retreading operations

Buffings are a by-product of tire retreading processes and/or solid tire recycling processes. During this process the remaining tread of a tire is peeled off by means of steel brushes. This process prepares the tire for reuse by e.g. gluing a new tread on to the brushed-off and cleaned tire carcass. Certain fractions of buffings are highly demanded by molding companies (e.g. for the production of playground mats). Mixed with rubber granulates the lengthy appearance of the buffings greatly increases tensile strength and elongation at break values of the finished products. Due to the lengthy shape this material is usually not recommended for in-situ construction purposes. Only few companies specialize on the treatment of buffings. Usually a separate line for classification is required. Oversizes should be regrinded, whereby fine buffing powders can usually easy be sold to compounding companies.

040527 rubber granulates - picture 040527 buffings - picture
Pictures: Comparison rubber granulates (cubical) vs. buffings (longish) (source: Robert Weibold GmbH)

 

Click here to read the first article from the Weibold! Academy series!

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