From tyre to compound

Ecopneus has developed a new method for modifying the powder obtained from recycling end-of-life tyres: developing a high performance, environmentally friendly thermoplastic compound

Sustainability and recycling are two terms used with increasing frequency to describe the global change that is impacting a number of production sectors transversally, and that goes by the name, “circular economy”. Translating these concepts into reality, however, is anything but simple: valid technical solutions are indeed needed, supported by specific know-how and knowledge, but also by long-term vision. These are the building blocks for the Tyreplast project, sponsored by Ecopneus, one of the leaders in the management of end-of-life tyres (ELTs) in Italy, with the technical support of Idea Plast (more information on page 28), a company specializing in support at the development of products and projects for the recycling  and reuse of the plastic. The concept of the project is to utilize the rubber powder from recycling ELTs through new applications in the thermoplastic sector.

A sustainable filler

During the course of the project, ELT powder was transformed from a mere inert material into a unique filler a at a contained cost to develop new thermoplastic compounds, as well as other products, capable of attributing interesting technical qualities to the final product, for example, better soundproofing and anti-vibration properties. In the context of improved environmental sustainability, research has focused not just on post-consumer filler material, but also on the use of fully recycled polymer matrices: in fact, post-consumer and urban waste resins were used – like HDPE, post-consumer polyolefins, PP, PA 6, rPET and SEBS – filled with quantities of powder varying from 10% to 50% depending on the type of product. In order to evaluate the potential of these “sustainable” materials, an experiment was also conducted on the same raw materials in virgin grade.

Without the addition of a compatibiliser, the powder struggles to disperse in the polymer matrix (SEM image)

The addition of compatibiliser improves dispersion of the ELT powder in the polymer matrix (SEM image)

The experiment

Research was conducted in three stages, namely the selection of suitable powder, the choice of the type and quantity of compatibiliser to use, and then the tests for evaluating the sound proofing properties of the materials.

The most suitable type of powder was identified first of all, according to the cleaning characteristics of the product, the granulometric quality and chemical stability, and then for the best balance between technical performance and price. The selection of the compatibiliser – fundamental for the success of the project – involved the collaboration of CNR–ISMAC in Genoa, which conducted some specific tests using different matrices: recycled polyolefin blend and virgin polypropylene, TPE, polyamide 6 and recycled PET flakes. The results of the analysis conducted by scanning electronic microscopy (SEM) showed that the powder struggles to disperse in the polymer matrix (figure 1), while when a compatibiliser is present, dispersion improves significantly (figure 2). Moreover, as demonstrated by the greater variability in some parameters (figure 3), the materials obtained without additives were less homogeneous.
Once the blends and additives have been identified, some samples were produced using a laboratory extruder; in this stage technical data sheets were also developed containing information on mechanical, thermal and chemical properties, useful for subsequent experimentation by processors.

Variability in the dispersion of results between samples with and without compatibiliser

The elastic modulus and elongation at break values permitted some possible applications to be identified in sectors that do not involve too harsh mechanical stress, but do require soundproofing and anti-vibration properties. Tests for evaluating the soundproofing properties of materials – analysing in detail the influence of the powder on these parameters and also evaluating the degree of vibration dampening and thermal isolation – returned good results.
The experiment also showed that the addition of powder modifies the size stability properties of the matrix, reducing creep in a more or less accentuated manner according to the matrix selected and the relative MFR. This, however, does not influence the processing conditions. Molding tests indeed demonstrated no substantial variability in process parameters, indicating that normal injection machines present in the department can be used without modification. Even calendering tests with powder filler content of up to 50% did not pose particular processing problems.

ELTs: a valuable resource
Each year, in Europe, approximately 3 million tons of tyres reach the end of their life. In Italy, in 2016 alone, Ecopneus collected and handled 252,384 tons of ELTs, equal to about 70 per cent of the national total, using them for material or energy recycling. The processing of ELTs takes place in dedicated plants, where they are reduced into pieces between 5 and 40 centimetres in size. In addition to rubber, ELTs still contain textile and metallic fragments, and can be sent for energy recycling (for example, in cement works) or undergo additional processing to reduce the size and separate the various materials making up the ELTs. Through a second grinding stage, the material is reduced to smaller parts and divided, through physical or mechanical techniques, into the three main components of the ELTs: rubber, steel and textile fibre. The rubber is ground once again and then the recycling process begins. The fragments are than classified into two product families, characterised by different sizes: rubber granules (between 0.8 and 20 mm) and rubber powder (less than 0.8 mm) without textiles and metals.

A new end-of-life approach

In the final stage of the experiment, the technicians of Idea Plast and Ecopneus tested the performance of new compounds in real applications, selected with industrial partners who operate in the building industry and the urban design sector, and tests in technical environments are ongoing. The results and feedback from the early users have encouraged the two partners of the Tyreplast project to undertake increasingly targeted dissemination, that will lead not only to greater use of ELT powder in compounding, but also a more knowledgeable approach to managing end-of-life products, where the recycled material must be considered to be a resource and not a problem. This is also the highest sense of the “circular economy” toward which the strategic decisions by the European Union and entire production sectors in member states are headed: combining environmental protection, scientific research and the industrial world for a more prosperous and sustainable future economy.

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