Analysis run by F.lli Maris through LCA methodology on the patented devulcanization process using a co-rotating twin-screw extruder, EVOREC RUBBER line
Introduction
The aim of this study is to investigate the environmental impacts of the patented Maris devulcanization process by using a co-rotating twin-screw extruder (EVOREC RUBBER line); the investigated recycled materials are gaskets in ethylene-propylene diene monomer (EPDM), sulfur vulcanized, deriving from the automotive sector. The study has been performed in collaboration with Department of Chemistry and NIS – INSTM, University of Turin.
Maris devulcanization process is a thermo-mechanical process that doesn’t involve the use of devulcanizing agents, supercritical CO2 or solvents. It is possible to devulcanize different rubber curing systems (for instance sulfur base or peroxide base). Although different thermo-mechanical devulcanization processes by co-rotating twin-screw extruders (cTSE) have been proposed, their practical implementation has not been completely satisfactory till now.
Devulcanization produces a second raw material from a free-flowing form feedstock which is produced by sorting and grinding operation, obtaining a re-usable material in a virgin blend without altering its characteristics. The inlet feedstock needs to be contaminants free – especially metal contamination. The feedstock quality in terms of homogenization and selection is one of the main fundamental factors to get a good quality devulcanized material.
The methodology used to perform the analysis of environmental impacts is the LCA and data used to configure the system refer to a real plant – Maris EVOREC RUBBER line, with a 58mm c-TSE – that carries out the devulcanization of EPDM waste from automotive gaskets.
Goal and scope definition
The analysis examined the production of the integrated system that allows the devulcanization process of 120 kg/h of EPDM. The goal was to demonstrate how the devulcanization process allows to reduce environmental burden associated with the life cycle of rubber product. In those terms, through the quantification of resources, energy consumption, emission and waste it is possible to calculate the environmental burden of a product or a process.
LCA calculation
The first step of the study was the definition of the boundary (Fig. 2) for the analysed system (Fig. 1).
The second step was the Inventory Analysis with the aim of identifying and quantifying the raw materials, resources, energy consumption, outputs and emission related to the functional unit considered.
Finally the third step was the impact assessments where the set of resources and emissions from the previous step are converted into a series of environmental impact categories. To determine the relative contribution of the considered categories. To determine the relative contribution of the considered categories, the impact were also assessed on a global level by normalization.


Comparative analysis
The study was extended by including two comparative analyses.
To highlight the impact generated by the production step, in the first comparison the production of 1 kg of virgin EPDM compound (v-EPDM) with 1 kg of EPDM obtained from EVOREC RUBBER process has been considered. a “cut-off” system was considered which involve the exclusion from the system boundaries of all the impacts attributable to the previous life of the material.
The second comparison (Fig.3) takes into account the different physicochemical properties of the devulcanized material and the virgin one, comparing two different system models, each of which allows to obtain two rubber products. For System 2 the product 2 is the combination of 30% of r-EPDM and 70% of v-EPDM which shows the same physicochemical properties of a product generated using 100% of virgin rubber (System 1).
It can be observed that in System 1 the end-of-life phase occurs by incineration, while in System 2 the first product undergoes a devulcanization process that allow its recycling and there is a 5% loss of material during the devulcanization process due to loss of material.
As shown, the analysis of the two system is greatly simplified if the equivalent processes are neglected (boxes crossed out in red).
For System 1, only impacts associated with the incineration process of 1 kg of rubber and the production of 3.15 kg of virgin EPDM compound need to be considered. Instead, for System 2, it’s enough to consider the impacts for the devulcanization process, which allows to obtain 0.95 kg of r-EPDM, and the impacts to produce 2.2 kg of v-EPDM compound.

Comparative analysis – first comparison
The devulcanization process allows to obtain EPDM with considerably lower impacts compared to the virgin one. In fact, the value for the r- EPDM is on average one order of magnitude smaller than those calculated for v-EPDM. Fig. 4 shows the comparison between the normalized environmental impacts of 1 kg of v-EPDM and r-EPDM.

The normalized results were reported to show the relative contributions of the impacts among the considered categories, when switching from v-EPDM to r-EPDM. As regards the v-EPDM, the most relevant impact is related with the category Resource use (fossils) that is mainly caused by the energy consumption, from the Italian national mix, during the phases of the devulcanization process.
Comparative analysis – second comparison
Fig. 5 shows that impacts generated in System 2, configurated assuming one recycling phase of the EPDM, are lower than impacts in System 1 (modelled using always virgin EPDM); this trend is common for all impact categories.

For both compared systems, the main impacts are obtained for the category Resource use (fossils).
In conclusion, both comparisons made in this study underline how recycled EPDM, obtained through a thermo-mechanical devulcanization process, allows to limit the environmental impacts compared to the production of virgin material.