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. 2022 Nov 11;14(22):4853.
doi: 10.3390/polym14224853.

Recycling of EPDM via Continuous Thermo-Mechanical Devulcanization with Co-Rotating Twin-Screw Extruder

Valentina Brunella  1 , Veronica Aresti  1 , Umberto Romagnolli  2 , Bruno Muscato  2 , Marco Girotto  2 , Paola Rizzi  1 , Maria Paola Luda  1
Affiliations

Recycling of EPDM via Continuous Thermo-Mechanical Devulcanization with Co-Rotating Twin-Screw Extruder

Valentina Brunella et al. Polymers (Basel). .

Abstract

Devulcanization represents the recycling of choice for a homogenous rubber waste stream because it allows revulcanization of samples previously devulcanized, making the life of the rubber virtually endless, according to the principles of circular economy. Among the many devulcanization processes, the thermo-mechanical one is the most appealing because it is a continuous process, easy to be industrialized. In this paper a comprehensive set of analyses (FTIR, TGA, DSC, elemental analyses, Py-GC/MS, swelling tests) were carried out on a post-industrial ethylene propylene diene monomer (EPDM), thermo-mechanical devulcanized in a co-rotating twin-screw extruder with different process parameters (thermal and screw profile, rpm). Results of the swelling test according to the Flory-Rehner theory and Horikx analyses show that the higher the thermal profile and the higher the rpm, the higher is the percentage of devulcanization. The quality of the devulcanized sample in terms of sol fraction and percentage of random scissions depends on the process conditions. The screw profile concurs to the efficiency of the devulcanization: the different number of kneading elements and more in general the screw profile composition affects the percentage of devulcanization, making the results in some tests more dependent on the screw speed.

Keywords: EPDM; co-rotating twin-screw-extruder; devulcanization; recycling; waste valorization.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure A1
Figure A1
MS spectrum of 4-ethylidene-1-cyclopentene, r.t 3.39 min.
Figure A2
Figure A2
MS spectrum of 3-ethylidene-1-cyclopentene r.t 3.45.
Figure A3
Figure A3
MS spectrum of benzothiazole, r.t 11.17 min.
Figure A4
Figure A4
MS spectrum of methylbenzothiazole, r.t 12.19 min.
Figure A5
Figure A5
MS spectrum of 2-(methyl mercapto)benzothiazole r.t 16.17 min.
Scheme 1
Scheme 1
(a) Reclamation; (b) Devulcanization.
Figure 1
Figure 1
Extrusion layout-Maris EVOREC RUBBER. 1. Extruder, 2. gravimetric feeder, 3. gravimetric pump, 4. side degassing unit, 5. vacuum pump, 6. water bath, 7. cooling and drying belt, 8. devulcanized rubber strip.
Figure 2
Figure 2
FTIR of RM EPDM, either original or extracted or after-SW. Blue line: original; orange line: extracted; red line: after SW.
Scheme 2
Scheme 2
Mechanism of formation of 4-ethylidene-1-cyclopentene (and 3-ethylidene-1-cyclopentene) from 5-ethylidene-2-norbornene unvulcanized units of EBN-EPDM by pyrolysis.
Figure 3
Figure 3
Pyrogram of the extracted EPDM RM.
Scheme 3
Scheme 3
Crosslinking mechanism for EBN-EPDM with benzothiazole-based accelerators and mechanism of formation of benzothiazole from ENB monosulfide residue from EPDM vulcanized with sulfur and 2-mercaptobenzothiazole accelerator.
Figure 4
Figure 4
Molecular ion extracted pyrograms of: (a) RM after-acetone extraction; (b) RM after-SW; (c) a devulcanized sample (test 5) after-acetone extraction; (d) the same devulcanized sample after-SW.
Figure 4
Figure 4
Molecular ion extracted pyrograms of: (a) RM after-acetone extraction; (b) RM after-SW; (c) a devulcanized sample (test 5) after-acetone extraction; (d) the same devulcanized sample after-SW.
Figure 5
Figure 5
Composition of the original EPDM RM.
Figure 6
Figure 6
Composition of original RM and original devulcanized samples.
Figure 7
Figure 7
Tg values of original, after-extraction and after SW samples series.
Figure 8
Figure 8
Horikx plot: red circles represent samples devulcanized using screw 1, green circles screw 2, yellow circles screw 3, light blue circles screw 3 10% H2O, dark blue circles screw 3 15% H2O. Blue line refers to the random model and orange line to the crosslinking scission model according to Horikx models.
Figure 9
Figure 9
%sol and %random for all samples.
See this image and copyright information in PMC

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