Microwave devulcanization of Ground Tyre Rubber (GTR) and characterization of various types of GTR

Microwave Devulcanization of Ground Tyre Rubber (GTR) Microwave Devulcanization of Ground Tyre Rubber (GTR) and Characterization of Various Types of GTR Student : Anwar Faliq Bin Musidin Professor : Xavier Colom Fajula 10-Jun-15 [Type the abstract of the document here. The abstract is typically a short summary of the contents of the document. Type the abstract of the document here. The abstract is typically a short summary of the contents of the document.] Microwave Devulcanization of Ground Tyre Rubber (GTR) 1 Contents ACKNOWLEDGEMENT ................................................................................................................................. 3 ABSTRACT ................................................................................................................................................... 4 1. INTRODUCTION ................................................................................................................................... 7 1.1 Generation of End-of-Life Tyre .......................................................................................................... 7 1.2 Reclamation of End-of-Life Tyre ........................................................................................................ 7 1.3 Chemistry and Composition of Tyre Rubber ..................................................................................... 8 1.4 Types of Devulcanization ................................................................................................................ 10 1.4.1 Mechanical Devulcanization .................................................................................................... 11 1.4.2 Ultrasonic Devulcanization ....................................................................................................... 11 1.4.3 Chemical Devulcanization ........................................................................................................ 12 1.4.4 Biological Devulcanization........................................................................................................ 12 2. LITERATURE REVIEW ON MICROWAVE DEVULCANIZATION ............................................................. 13 2.1 Introduction to Microwave ............................................................................................................. 13 2.2 Microwave Devulcanization ............................................................................................................ 15 2.3 Studies on Microwave Devulcanization .......................................................................................... 15 3. EXPERIMENTAL ................................................................................................................................. 16 3.1 Materials ......................................................................................................................................... 16 3.2 Sample Preparation ........................................................................................................................ 19 3.3 Characterization of Microwave Devulcanization of GTR ................................................................. 20 3.3.1 Fourier Transform Infrared Spectroscopy (FTIR) ...................................................................... 20 3.3.2Thermogravimetric Analysis (TGA) ............................................................................................ 20 3.3.3 Crosslinking .............................................................................................................................. 21 3.3.4 Sol fraction ............................................................................................................................... 24 3.3.5 Ash content determination ...................................................................................................... 25 4. RESULTS AND DISCUSSION ................................................................................................................ 27 4.1 Fourier Transform Infrared Spectroscopy (FTIR) ............................................................................. 28 4.1.1 Analysis of FTIR spectra without microwave ............................................................................ 28 4.1.2 Analysis of the microwave devulcanized samples .................................................................... 31 4.2 Thermogravimetric Analysis ............................................................................................................ 37 4.3 Crosslink Density ............................................................................................................................. 44 Microwave Devulcanization of Ground Tyre Rubber (GTR) 2 4.4 Sol Fraction ..................................................................................................................................... 45 4.5 Ash content determination ....................................................................................................... 45 5. PROPOSED MECHANISM OF DEVULCANIZATION ........................................... 46ACKNOWLEDGEMENT 6. CONCLUSION..................................................................................................................................... 48 7. PROPOSALS ....................................................................................................................................... 49 BIBLIOGRAPHY .......................................................................................................................................... 50 ANNEX....................................................................................................................................................... 54 Microwave Devulcanization of Ground Tyre Rubber (GTR) 3 ACKNOWLEDGEMENT Upon the completion of the Final Project report, I would like to give my appreciation to Xavier Colom, the supervisor and mentor for my project. He has been very supportive and always shares his knowledge to my colleague and me throughout the project. I would like to thank Josep Maria Dagá, who have helped me in the initial phase of the project and explained some technical aspects regarding the background of the experiment. Not forget to mention my family who has always give advices and always believe in me to be able to complete the project. Last but not least, I would like to thank my friends and colleagues, Marina Cano, Ainur Safia, Ilya Syahira, Carlos and Oscar who have always lending me a hand in the laboratory when I am in need. With the completed report, it is of my best interest to be able to contribute and to enrich the academic community, and widen the understanding especially in the field of microwave devulcanization. Anwar Faliq Bin Musidin, Terrassa, 10th of June 2015 Microwave Devulcanization of Ground Tyre Rubber (GTR) 4 ABSTRACT Three types of ground tyre rubber (GTR) are treated with microwave in order to study the effect of microwave devulcanization. The first one is the standard GTR of truck (A1) and car (A2), mechanically reactivated GTR of truck (B1) and car (B2) and GTR which has been mechanically and chemically devulcanized (C1).Various analysis techniques have been used in order to characterize the devulcanizates produced under 0 minutes, 3 minutes, and 5 minutes of exposure to microwave. From the FTIR spectra, the most prominent result can be seen from the devulcanizates of mechanical reactivated GTR (B1). Various types of bonds such as methyl group, methylene group, carbon double bonds, and carbon-sulfur bonds have been reduced due to the decrease in peaks at certain bands. Microwave Devulcanization of Ground Tyre Rubber (GTR) 5 The Thermogravimetric Analysis (TGA) of the mechanically reactivated GTR for car (B2) and chemical and mechanical devulcanized GTR (C1) shows a direct relationship of decrease of inorganic residual as the exposure time to microwave increase. The crosslink density test of standard GTR of car (A2), B1 and B2 showed an increase in crosslink density as time of exposure increase. 54 56 58 60 62 64 66 0 1 2 3 4 5 Percentage of organic material decomposition (%) Microwave exposure time (min) Percentage of organic material decomposition (%) vs Exposure time (min) A1 A2 B1 B2 C1 2,00E-04 3,00E-04 4,00E-04 5,00E-04 6,00E-04 7,00E-04 8,00E-04 9,00E-04 0 1 2 3 4 5 Average Crosslink density (mol/cm3) Microwave exposure time (min) Average Crosslink density (mol/cm3) vs Exposure time (min) A1 A2 B1 B2 C1 Microwave Devulcanization of Ground Tyre Rubber (GTR) 6 The sol fraction test was done by using acetone and all samples showed an increase in sol content as time of exposure increases. 9 14 19 24 29 0 1 2 3 4 5 Sol fraction (%) Microwave exposure time (min) Sol fraction (%) vs Exposure time (min) A1 A2 B1 B2 C1 Microwave Devulcanization of Ground Tyre Rubber (GTR) 7 1. INTRODUCTION 1.1 Generation of End-of-Life Tyre The development and rapid growth of the automotive industry as well as high demands of passenger and commercial vehicles around the world have contributed to positive impacts on the economy and job creation. However, there are also environmental problems that arise from this industry. One of them is the generation of End-of-Life Tyre (ELT). The global output of tyre is estimated at 1,5 billion units [1] and in 2008, the amount of ELTs generated were 3,4 million tonnes in Europe and 238.529 tonnes in Spain [2]. The poor disposal of tyres in may affect human health as it becomes a breeding ground for mosquitoes and rodents. Due to the slow decomposition of tyres, it poses other environmental risk such as fire. 1.2 Reclamation of End-of-Life Tyre Unlike other materials such as papers which can be recycled and manufactured into new products, the composition and the chemical structure of tyre hinders the process of recycling. The tyres are made by sulfur vulcanization of natural rubber or synthetic rubber with the addition of other additives and cured at a high temperature [3]. The result is the formation of crosslinks due to sulfur bridges which connects the carbons of the backbone chains in the rubber. The vulcanization process increases the mechanical properties of rubber and the formation of sulfur bridges are irreversible. From 1996 to 2010, the methods of dealing with the ELTs in Europe have improved, where the amount of ELTs that were dumped into the landfill reduced from 49% to 4% [1]. The rest of the ELTs are sorted according to their physical attributes. The damaged and worn out tyres are used in combustion for energy generation in boilers, power plants and kiln. Other than energy generation, the ELTs are recycled and reclaimed for the use in civil engineering and public works such as rubber mats used in playgrounds and running tracks and blended with asphalt for the use in road construction [4]. The tyres which are in a good condition or partially worn out are retreaded, reused and sent for export. The idea of retreading and reusing the tyres is considered good for the environment as there is less energy and raw materials (mineral oil, synthetic and natural rubber, etc.) used than the manufacture of new ones [5] [6]. Unfortunately, several reclaiming methods are detrimental to the environment. Such example is the obtention of energy from combustion of old tyres, which has caused debates among the members of the public due to the emission of hazardous pollutants that can cause negative health effects and problems to the environment [7] [8]. Microwave Devulcanization of Ground Tyre Rubber (GTR) 8 Since the mentioned reclaiming method does not really break the crosslinks formed from the vulcanization process inside the tyre, there are studies made for devulcanization of ground tyre rubber (GTR). The devulcanizates produced are then made into new composite materials by mixing it with fresh synthetic or natural rubber [9]. The objective of making this composite material is to enhance the mechanical properties and hence, adding the value to the GTR. 1.3 Chemistry and Composition of Tyre Rubber Before going further into the process of devulcanization, there is a need to understand the components that make up the tyres and its microstructure. The common compositions of tyres are given in the table below: Table 1: The compositions (in percentage) of car, truck and off-the-road tyre [10]. Component Car Tyre (%) Truck Tyre (%) Off-the-road Tyre (%) Rubber/ Elastomers 47 45 47 Carbon Black 21,5 22 22 Metal 16,5 25 12 Textile 5,5 -- 10 Zinc Oxide 1 2 2 Sulfur 1 1 1 Additives 7,5 5 6 Total of Carbon-based materials 74 67 76 The elastomers used in each type are usually a mix of natural and synthetic rubber and the proportions differ from one another. Natural rubber has the chemical name of cis-1,4-polyisoprene and used in higher proportion than synthetic rubber in truck and off-the-road tyre. This is due to the fact that natural rubber builds up less heat when flexed and has greater resistance from tearing at an elevated temperature [11]. The synthetic rubber used is a copolymer of styrene-butadiene rubber (SBR) and has higher proportion in car tyres, mainly because it is cheaper and relatively good resistance from abrasion compared to natural rubber [12]. Microwave Devulcanization of Ground Tyre Rubber (GTR) 15 2.2 Microwave Devulcanization In microwave devulcanization, C-S (260 kJ/mol) and S-S (225 kJ/mol) bonds are expected to be broken when microwave is applied. Theoretically, the heating of GTR happens at specific points [40], near the polar groups and hence, reducing the degradation of the main backbone chains [41]. However, it is possible that the microwave provides more than enough energy. If that is the case, the C-C (350 kJ/mol) and C=C (611 kJ/mol) [42] of the rubber backbone chain may also be broken and degradation of the devulcanizates may occur. In the case of GTR, aside from the rubber component, there is also carbon black, oxide of silica and other additives which have its own dipole rotation when microwave is applied. 2.3 Studies on Microwave Devulcanization One of the earliest study on microwave was a patent awarded to Goodyear Tire in 1978 and claimed that the application of 41Wh – 177 Wh per pound of EPDM rubber is sufficient to break the C-S and S-S bonds but not enough to break C-C bonds [43]. Roussy et al. found that the devulcanization of EPDM rubber happened at 280 oC. Karabork et al. [44] made a composite of SBR with microwave devulcanized GTR. The devulcanized GTR was analysed using thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The thermogram form the TGA showed that the residue was 35 % of the original weight and corresponds to the additives used such as silica and carbon black. The FTIR analysis proved that there are a breaking of S-S bonds and a few C-C and C-S bonds were broken due to the microwave devulcanization. Similar study by A. Zanchet et al used microwave devulcanized SBR scraps and made a composite by mixing it with fresh SBR [45]. The remaing residue from the thermogram was between 41 to 45 % of the original weight. The difference of residual % from the previously mentioned study was mainly due to the difference of composition of SBR and GTR. D. Hirayama did a study on microwave devulcanization of SBR and proved by FTIR the breakdown of S-S bonds and a few C=C bonds. The absence of C=C bonds may affect negatively if it were to be made into composites because the C=C bonds are needed for the formation of sulfur crosslinks. The tensile strength of the composites made from the devulcanizates by Karabork et al. [44] and A. Zanchet [45] increased, but only in a specific amount of devulcanizates. The exposure to microwave also differs for GTR and scrap SBR in order to achieve the desired increase in physical properties. Microwave Devulcanization of Ground Tyre Rubber (GTR) 16 3. EXPERIMENTAL 3.1 Materials There are three types of samples used in this experiment. The first one is the standard GTR of truck (A1) and car (A2). The second is the mechanically reactivated GTR of truck (B1) and car (B2). The last sample is the GTR which has been mechanically and chemically devulcanized previously (C1). Samples A1, A2, B1 and B2 have more or less the same texture and feels like a fine powder when touched. Meanwhile, C1 has a different texture to it. It feels crumbly and loosely packed. When a little pressure is applied, it turns into a fine powder. These GTR samples are obtained from Gestión Medioambiental de Neumáticos S. L. (GMN) and have an average particle size of between 400 to 600 microns. Potassium bromide is used to make the pellet for the FTIR analysis of the GTR. Acetone is used in the determination of sol content of the GTR and toluene is used in determining the crosslink density for the swelling test and is obtained from Panreac Química S.L.U. Figure 3: GTR used for microwave devulcanization. Type of GTR Figure A1-Truck Standard GTR Microwave Devulcanization of Ground Tyre Rubber (GTR) 17 A2-Car Standard GTR B1-Truck Mechanically Reactivated GTR Microwave Devulcanization of Ground Tyre Rubber (GTR) 18 B2-Car Mechanically Reactivated GTR C1-Chemical & Mechanical Devulcanizati on Microwave Devulcanization of Ground Tyre Rubber (GTR) 19 3.2 Sample Preparation The microwave devulcanization process is done by using a modified domestic microwave oven, Daewoo KOR-6L35 with the maximum power output of 700 W. A stirrer is added to the microwave and is made of polytetrafluoroethylene to ensure even exposure of microwave to the GTR. During the devulcanization process, around 15 g of each GTR sample is placed inside a 300 ml beaker. The stirrer is set at 20 rpm. The samples are then exposed to the microwave treatment for 0, 3 and 5 minutes at 700 W. After each treatment, the temperature of the devulcanizates is recorded. Figure 4: The setup of modified microwave oven with stirring system. Microwave Devulcanization of Ground Tyre Rubber (GTR) 20 3.3 Characterization of Microwave Devulcanization of GTR The microwave treated samples are then characterized using a few analysis techniques: 3.3.1 Fourier Transform Infrared Spectroscopy (FTIR) 5 to 6 mg of each sample is incorporated into 300 mg of potassium bromide and grinded into fine powder. The sample and powder are formed into pellet by using Specac pellet hydraulic press at 10 tonnes of force. The spectrometer used is Nicolet Avatar 320 FTIR, equipped with CsI optics. Any changes of GTR microstructure before and after the microwave treatment can be observed by using the spectra produced. Figure 5: Nicolet Avatar 320 FTIR Spectrometer (left) and some of the KBr with GTR pellet used (right). 3.3.2Thermogravimetric Analysis (TGA) Each sample is analysed using Mettler Toledo TGA/SDTA 851. About round 13,5 mg of sample is placed inside an alumina crucible. The measurement is conducted in an inert environment, with a flow rate of 20 ml/min of nitrogen gas and heating rate of 20 oC/min. The temperature starts at 40 oC and ends at 600 oC. The TGA enables us to determine any changes of composition of GTR and the decomposition curve. Microwave Devulcanization of Ground Tyre Rubber (GTR) 21 Figure 6: Mettler Toledo TGA used in the analysis. 3.3.3 Crosslinking The crosslinking test is done by making a sheet of rubber made from the GTR. 61 g of GTR of each sample is put into a square mould of outside dimension 19 cm x 19 cm and inside dimension of 16 cm x 16 cm with a thickness of 0,26 cm with steel plates. The mould is then pressed using Collin P200E hot plate press at a temperature of 220 oC for 12 minutes. The obtained rubber sheet is then removed from the mould and is cut into tiny squares of . Figure 7: Collin P200E hot plate press used in making the rubber sheet. Microwave Devulcanization of Ground Tyre Rubber (GTR) 22 Figure 8: Square mould for making the rubber sheet. Figure 9: The cut rubber sheet used for swelling test with toluene. The diagram shows the dried sample (left) and the swollen sample (right). The dimension is recorded to calculate the volume and the weight is recorded. The tiny squares from various part is then soaked inside a small container containing about 2 ml of toluene for 72 hours. After that, the swollen specimen is weighed and left to dry for 24 hours at room temperature. The weight of the dried specimen is recorded once again. The crosslink density can be calculated using Flory-Rehner equation [46]: Microwave Devulcanization of Ground Tyre Rubber (GTR) 23 Equation 2: Flory-Rehner equation ( ) ( ) Where: Crosslink density (mol/cm3) Molar volume of solvent - toluene (106,13 cm3/mol) [46] Rubber solvent interaction parameter (0,3795) [44] Volume fraction of rubber in swollen sample The volume fraction of rubber in swollen sample is calculated by using the following equation: Equation 3: Formula to calculate the volume fraction of rubber [47] ( ) ( ) ( ) Where: Weight of swollen specimen Weight of the dried specimen (24 hours at room temperature) Density of solvent – toluene (0,8669 g/cm3) [48] Density of the specimen Crosslinking density refers to presence of crosslink inside the specimen. The solvent did not dissolve the network of crosslinks, but instead swells it by entering the spaces inside the crosslink cluster. The following illustrates the network of crosslinks: Microwave Devulcanization of Ground Tyre Rubber (GTR) 24 Figure 10: The illustration of crosslink network inside a polymer [3] The solvent particles enter the crosslink cluster and as a result push the network junctions away from each other. The higher the value of crosslink density, the network junction moves away less and there is less volume expansion of the specimen due to swelling [49]. 3.3.4 Sol fraction The sol content refers to the soluble part of the sample. The determination of sol fraction is done by Soxhlet extraction, using acetone as the solvent. Figure 11: The Soxhlet extractor (left) and the cellulose thimble used (right) Microwave Devulcanization of Ground Tyre Rubber (GTR) 31 4.1.2 Analysis of the microwave devulcanized samples In this part, the FTIR spectra of all the samples which have undergone microwave treatment is presented and discussed. A1 Spectra FTIR Spectra 3: Spectra for A1 at 0, 3, and 5 minutes of microwave exposure. In A1 spectra, there seems to be no change in methyl group (1385 cm-1), sulfur bridge (470 cm-1), carbon-sulfur bond (611 cm-1), methylene group (710 cm-1). However, there is a decrease in C=CH (1018 cm-1) due to the microwave devulcanization and an increase in SiO2 (1092 cm-1) content, most probably due to oxidation. In this case, backbone chain breaking is happening. Microwave Devulcanization of Ground Tyre Rubber (GTR) 32 A2 Spectra FTIR Spectra 4: Spectra for A2 at 0, 3, and 5 minutes of microwave exposure between 1800 cm-1 to 1200 cm-1. With the microwave time of 5 minutes, the peak at 1437 cm-1 is very prominent and corresponds to the (CH2) scissoring. FTIR Spectra 5: Spectra for A2 at 0, 3, and 5 minutes of microwave exposure between 1500 cm-1 to 900 cm-1. 1093 1382 1410 1021 GTR A25 GTR A23 GTR A20 1000 1200 1400 Wavenumbers (cm-1) There is an increase in 1440 cm-1 and 1993 cm-1 (SiO2) while a reduction of the band 1385 cm-1 and 1021 cm-1 (black carbon) and confirms that the microwave treatment reduce the quantity of black carbon. 1382 1410 1629 GTR A23 GTR A20 GTR A25 1200 1400 1600 1800 Wavenumbers (cm-1) Microwave Devulcanization of Ground Tyre Rubber (GTR) 33 FTIR Spectra 6: Spectra for A2 at 0, 3, and 5 minutes of microwave exposure between 800 cm-1 to 400 cm-1. B1 Spectra FTIR Spectra 7: Spectra for B1 at 0, 3, and 5 minutes of microwave exposure. 459 716 GTR A20 GTR A23 GTR A25 500 600 700 800 Wavenumbers (cm-1) Microwave Devulcanization of Ground Tyre Rubber (GTR) 34 In B1 spectra, there is a reduction of –CH3 group (1383 cm-1 ), SiO2(1111 cm-1) , C=CH (1022 cm-1) , -CH2 (713 cm-1) and C-S (606 cm-1 and 586 cm-1). In this case, there is more backbone chain breaking compared to the A1 and A2 sample and still no decrease in S-S bridge (466 cm-1). B2 Spectra FTIR Spectra 8: Spectra for B2 at 0, 3, and 5 minutes of microwave exposure from 1800 cm-1 to 1100 cm-1. For B2, there is a decrease in peak at 1407 cm-1 which corresponds to the breaking of backbone chain =CH2. 1384 1407 1463 1633 GTR B20 GTR B25 GTR B23 1200 1400 1600 1800 Wavenumbers (cm-1) Microwave Devulcanization of Ground Tyre Rubber (GTR) 35 FTIR Spectra 9: Spectra for B2 at 0, 3, and 5 minutes of microwave exposure from 1500 cm-1 to 800 cm-1. FTIR Spectra 10: Spectra for B2 at 0, 3, and 5 minutes of microwave exposure from 800 cm-1 to 400 cm-1. The peak at 716 cm-1 (-CH2-) ,611 cm-1 and 524 cm-1 (both C-S) show a decrease of peak when exposed to microwave for 5 minutes and confirms the bond breaking. However the band at 465 cm-1 (S-S) do not change and no sulfur bridge breaking occurs. 1037 1384 1407 1463 1101 GTR B20 GTR B25 GTR B23 1000 1200 1400 Wavenumbers (cm-1) 465 524 611 716 *GTR B23 *GTR B20 *GTR B25 500 600 700 Wavenumbers (cm-1) Microwave Devulcanization of Ground Tyre Rubber (GTR) 36 C1 Spectra FTIR Spectra 11: FTIR spectra for C1 at 0, 3, and 5 minutes of microwave exposure. In the spectra of C1, there is practically no change in peak except a decrease of peak at 1117 cm-1 (SiO2), as the exposure time to the microwave increases. The decrease of inorganic residue such as SiO2 means the microwave increases the decomposition of organic components of GTR and proves the changes in microstructure. 872 456 710 1022 1117 1384 GTR C3 *GTR C0 *GTR C5 600 800 1000 1200 1400 Wavenumbers (cm-1) Microwave Devulcanization of Ground Tyre Rubber (GTR) 37 4.2 Thermogravimetric Analysis TGA Curve 1: Curve for A1 at 0, 3, and 5 minutes of microwave exposure. TGA Curve 2:Differential TGA curve for A1 at 0, 3, and 5 minutes of microwave exposure. Sample: GTR A10, 13,4700 mg Sample: GTR A15, 13,5900 mg Sample: GTR A13, 13,4620 mg Step -60,5077 % -8,2230 mg Step -60,9876 % -8,2150 mg Step -59,8634 % -8,0588 mg mg 5 6 7 8 9 10 11 12 13 14 min °C50 10 0 15 0 20 0 250 300 35 0 400 45 0 50 0 550 0 2 4 6 8 10 12 14 16 18 20 22 24 26 STARe S W 1 2 . 1 0E E T-UP C B arc el onaTE CH: M E TTLE R Sample: GTR A 13, 13,4620 mg Sample: GTR A 15, 13,5900 mg Sample: GTR A 10, 13,4700 mg mgmin^ -1 -1, 6 -1, 4 -1, 2 -1, 0 -0, 8 -0, 6 -0, 4 -0, 2 0, 0 min °C50 10 0 15 0 200 250 30 0 35 0 40 0 45 0 50 0 550 0 2 4 6 8 10 12 14 16 18 20 22 24 26 STARe S W 1 2 . 1 0E E T-UP C B a rc e l on a TE CH: ME TTLE R Microwave Devulcanization of Ground Tyre Rubber (GTR) 38 TGA Curve 3: Curve of A2 at 0, 3, and 5 minutes of microwave exposure. TGA Curve 4: Differential TGA curve of A2 at 0, 3, and 5 minutes of microwave exposure. Sample: GTR A 23, 13,7000 mg Sample: GTR A 20, 13,5000 mg Sample: GTR A 25, 13,5000 mg Step -64,1567 % -8,7895 mg Step -61,8821 % -8,3541 mg Step -57,0205 % -7,6978 mg mg 5 6 7 8 9 10 11 12 13 14 min °C50 10 0 15 0 20 0 25 0 30 0 35 0 400 450 500 550 0 2 4 6 8 10 12 14 16 18 20 22 24 26 STARe S W 1 2. 10E E T-UP C B a r c el ona TE CH: M E TTLE R Sample: GTR A25, 13,5000 mg Sample: GTR A20, 13,5000 mg Sample: GTR A23, 13,7000 mg mgmin^ -1 -1, 4 -1, 2 -1, 0 -0, 8 -0, 6 -0, 4 -0, 2 0, 0 min °C50 10 0 15 0 20 0 25 0 30 0 35 0 40 0 45 0 50 0 55 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 STARe S W 12. 1 0E E T-UP C B arc el ona TE CH: ME TTL E R Microwave Devulcanization of Ground Tyre Rubber (GTR) 39 TGA Curve 5: TGA curve of B1 at 0, 3, and 5 minutes of microwave exposure. TGA Curve 6: Differential TGA curve of A1 at 0, 3, and 5 minutes of microwave exposure. Step -61,8219 % -8,3954 mg Step -59,8907 % -8,0852 mg Step -60,8470 % -8,2143 mg Sample: GTR B10_2, 13,5800 mg Sample: GTR B13_2, 13,5000 mg Sample: GTR B15, 13,5000 mg mg 5 6 7 8 9 10 11 12 13 14 min °C50 10 0 15 0 20 0 25 0 30 0 35 0 400 450 500 55 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 STARe S W 12 . 10E E T-UP C B a rc e l o naTE CH: M E TTL E R Sample: GTR B15, 13,5000 mg Sample: GTR B13_2, 13,5000 mg Sample: GTR B10_2, 13,5800 mg mgmin^ -1 -1, 4 -1, 2 -1, 0 -0, 8 -0, 6 -0, 4 -0, 2 0, 0 min °C50 10 0 15 0 20 0 25 0 30 0 35 0 40 0 45 0 50 0 55 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 STARe S W 12. 1 0E E T-UP C B arc e l o n aTE CH: M E TTLE R Microwave Devulcanization of Ground Tyre Rubber (GTR) 40 TGA Curve 7: Curve of B2 at 0, 3, 5 and 8 minutes of microwave exposure. TGA Curve 8: Differential TGA curve of B2 at 0, 3, 5 and 8 minutes of microwave exposure. mg 5 6 7 8 9 10 11 12 13 14 min0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 Step -55,4784 % -7,5051 mg Step -58,0535 % -7,7850 mg Step -56,1620 % -7,5426 mg Step -59,3199 % -8,0082 mg &B28 B28, 13,5000 mg &B23 B23, 13,4300 mg >R B25 wN2 GTR B25 wN2, 13,4100 mg >R B20 GTR B20, 13,5280 mg mg 5 6 7 8 9 10 11 12 13 14 °C50 10 0 15 0 20 0 250 300 350 400 45 0 50 0 55 0 STARe S W 12 . 10E E T-UP C B a rc e l o n aTE CH: ME TTLE R mg 5 6 7 8 9 10 11 12 13 14 min0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 Sample: B28, 13,5000 mg Sample: B23, 13,4300 mg Sample: GTR B25 wN2, 13,4100 mg Sample: GTR B20, 13,5280 mg mg°C^-1 -0, 05 5 -0, 05 0 -0, 04 5 -0, 04 0 -0, 03 5 -0, 03 0 -0, 02 5 -0, 02 0 -0, 01 5 -0, 01 0 -0, 00 5 0, 0 00 0, 0 05 °C50 10 0 15 0 20 0 25 0 30 0 35 0 40 0 45 0 50 0 55 0 STARe S W 12. 1 0E E T-UP C B arc el ona TE CH: M E TTLE R Microwave Devulcanization of Ground Tyre Rubber (GTR) 47 After the treatment, the S-S bonds remains constant, while the backbone chain is broken. The SiO2 is no longer attached to the elastomer and the carbon black has been converted into CO2. During Microwave Treatment After Microwave Treatment Initial network Microwave Devulcanization of Ground Tyre Rubber (GTR) 48 6. CONCLUSION From the FTIR spectra of all the samples, the spectrum of B1 which is the mechanical reactivated for truck GTR gives us the best result. It has the most groups and bonds which are broken by microwave. The bonds broken are of –CH3 group, SiO2, C=CH, -CH2 and C-S. However, the microwave process did not break the S-S bonds, which is the main purpose of the study. We can say that the microwave treatment works fairly well because even if there is no S-S bonds broken, there is still C-S bonds which are broken. The second conclusion that can be drawn from this study is that the microwave treatment does affect the elastomeric components (rubber backbone chains) as well as the inorganic components. The TGA proves the decrease in inorganic residue due to microwave process. These inorganic components of GTR may have been destroyed due to the friction of dipole rotation in it due to the application of microwave. The generated heat is great enough to convert it into CO2. The crosslinking test suggests that the revulcanization of the elastomer inside the GTR is possible due to the increase in crosslink density in the rubber sheet. However, the temperature must be sufficiently high in order to reactivate the residual sulfur and C=C bonds which is responsible for sulfur bridge inside the elastomer. Further studies may be done to determine if the increase in crosslink density can improve the tensile strength of the formed rubber sheet. The first conclusion that can be drawn is that the chemical and mechanical devulcanized GTR (C1) has the least amount of microstructural and sol fraction change. Unlike the standard GTR and the mechanically reactivated GTR, C1 gives the least change be it in FTIR , crosslink density (between 3,4 x10-4 to 3,7 x10-4) and sol fraction percentage (between 9,5% to 15%) . The chemical and mechanical devulcanization process really affects the performance of the GTR. The second conclusion that we can get from this experiment is that the microwave treatment do increase the organic component decomposition by altering the microstructures of the GTR. This statement is backed by the result of FTIR and TGA. The final conclusion i, microwave devulcanization is suitable for certain types of GTR. This can be seen in sample C1, where all the characterization analysis proved that it has the smallest change in parameter of all the samples even if the exposure time to microwave is increased. Further studies can be done to Microwave Devulcanization of Ground Tyre Rubber (GTR) 49 ensure that the microwave devulcanization is suitable to be used on all types of GTR and gives a constant result. 7. PROPOSALS For future studies, the following points can be taken into account in order to improve the result of this experiment: a) For the crosslinking test, a new way to form the rubber sheet must be introduced. The hot plate press must be operated at a temperature lower than 160 oC to avoid revulcanization of the GTR. If it is possible, only use hight pressure to form the rubber sheet at a room temperature. As a result, the crosslink density can be decreased as the exposure time of microwave increase. If combined with the sol fraction obtained, the Horikx’s theory can be applied to relate whether a selective bond breaking can be achieved with microwave devulcanization. b) The rubber sheet can be cut into standard shape for tensile strength testing. 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Microwave Devulcanization of Ground Tyre Rubber (GTR) 54 ANNEX Annex 1: The table of crosslink density calculation. Sample Width (cm) Length (cm) Height (cm) Volume of Dry Sample, Vd (cm3) Weight of Dry Sample,Wd (g) Density of Sample, ρ2=Wd/Vd (g/cm3) Weight of Swollen Sample, a1 (g) Weight of Swollen Sample After Drying, a2 (g) Weight of Toluene Absorbed , a1-a2 (g) Volume Fraction of Rubber, Vr Crosslink Density, ρc (mol/cm3) A10(1) 0,960 1,200 0,260 0,30 0,324 1,082 0,897 0,296 0,601 0,283 3,53E-04 A10(2) 1,110 1,200 0,260 0,35 0,407 1,175 1,115 0,38 0,735 0,276 3,32E-04 A10(3) 1,290 1,050 0,250 0,34 0,389 1,149 1,07 0,356 0,714 0,273 3,24E-04 A10(4) 1,480 1,450 0,260 0,56 0,615 1,102 1,662 0,57 1,092 0,291 3,78E-04 A13(1) 1,200 1,180 0,270 0,38 0,383 1,002 0,831 0,302 0,529 0,331 5,25E-04 A13(2) 1,120 1,240 0,260 0,36 0,363 1,005 0,835 0,289 0,546 0,313 4,57E-04 A13(3) 1,160 1,320 0,250 0,38 0,424 1,108 0,923 0,332 0,591 0,305 4,27E-04 A13(4) 1,220 1,290 0,260 0,41 0,360 0,880 0,831 0,275 0,556 0,328 5,13E-04 A15(1) 1,020 1,000 0,260 0,27 0,279 1,052 0,785 0,246 0,539 0,273 3,24E-04 A15(2) 1,280 1,250 0,250 0,40 0,443 1,108 1,215 0,384 0,831 0,266 3,02E-04 A15(3) 1,180 1,080 0,240 0,31 0,360 1,177 0,982 0,313 0,669 0,256 2,77E-04 A15(4) 1,160 1,180 0,240 0,33 0,380 1,157 1,034 0,316 0,718 0,248 2,56E-04 A20(1) 1,470 1,210 0,260 0,46 0,462 0,999 1,381 0,439 0,942 0,288 3,68E-04 A20(2) 1,103 1,079 0,266 0,32 0,351 1,109 0,972 0,322 0,65 0,279 3,41E-04 A20(3) 1,164 1,138 0,266 0,35 0,360 1,022 1,026 0,338 0,688 0,294 3,89E-04 A23(1) 1,130 1,120 0,260 0,33 0,299 0,909 0,654 0,234 0,42 0,347 5,96E-04 A23(2) 1,125 1,167 0,249 0,33 0,349 1,068 0,831 0,295 0,536 0,309 4,40E-04 A23(3) 1,036 1,171 0,249 0,30 0,316 1,046 0,766 0,262 0,504 0,301 4,12E-04 A25(1) 1,040 1,220 0,260 0,33 0,336 1,019 0,797 0,271 0,526 0,305 4,25E-04 Microwave Devulcanization of Ground Tyre Rubber (GTR) 55 A25(2) 1,164 1,264 0,246 0,36 0,379 1,047 0,926 0,306 0,62 0,290 3,75E-04 A25(3) 1,381 1,157 0,247 0,39 0,415 1,052 0,753 0,344 0,409 0,409 9,40E-04 B10(1) 1,250 1,080 0,270 0,36 0,401 1,100 1,042 0,373 0,669 0,305 4,27E-04 B10(2) 1,221 1,118 0,284 0,39 0,409 1,055 1,109 0,384 0,725 0,303 4,20E-04 B10(3) 1,187 1,093 0,272 0,35 0,379 1,074 0,993 0,357 0,636 0,312 4,51E-04 B13(1) 1,110 1,360 0,260 0,39 0,389 0,991 0,889 0,354 0,535 0,367 6,91E-04 B13(2) 1,052 1,061 0,255 0,28 0,287 1,008 0,719 0,263 0,456 0,331 5,28E-04 B13(3) 1,025 1,324 0,256 0,35 0,376 1,082 0,924 0,343 0,581 0,321 4,86E-04 B15(1) 1,500 1,380 0,270 0,56 0,537 0,961 1,163 0,443 0,72 0,357 6,43E-04 B15(2) 1,365 1,131 0,272 0,42 0,393 0,936 0,828 0,313 0,515 0,360 6,59E-04 B15(3) 1,425 0,939 0,271 0,36 0,355 0,979 0,76 0,295 0,465 0,360 6,56E-04 B20(1) 1,090 1,090 0,270 0,32 0,363 1,132 0,887 0,337 0,55 0,319 4,80E-04 B20(2) 1,140 1,110 0,260 0,33 0,394 1,198 0,975 0,355 0,62 0,293 3,85E-04 B20(3) 1,160 1,380 0,270 0,43 0,492 1,138 1,203 0,45 0,753 0,313 4,54E-04 B23(1) 1,180 1,330 0,270 0,42 0,450 1,062 0,984 0,397 0,587 0,356 6,37E-04 B23(2) 0,960 1,250 0,250 0,30 0,345 1,150 0,761 0,297 0,464 0,325 5,04E-04 B23(3) 1,240 1,240 0,260 0,40 0,456 1,141 1,002 0,391 0,611 0,327 5,11E-04 B25(1) 1,300 1,400 0,270 0,49 0,354 0,720 0,726 0,297 0,429 0,454 1,27E-03 B25(2) 1,290 1,440 0,270 0,50 0,495 0,987 1,002 0,407 0,595 0,375 7,37E-04 B25(3) 1,360 1,140 0,260 0,40 0,431 1,069 0,862 0,349 0,513 0,356 6,36E-04 C10(1) 1,000 1,110 0,270 0,30 0,282 0,941 0,821 0,248 0,573 0,285 3,59E-04 C10(2) 1,047 0,875 0,257 0,24 0,221 0,939 0,667 0,194 0,473 0,275 3,28E-04 C10(3) 1,101 0,976 0,261 0,28 0,289 1,030 0,845 0,264 0,581 0,277 3,33E-04 C13(1) 1,020 0,940 0,260 0,25 0,254 1,019 0,742 0,224 0,518 0,269 3,11E-04 C13(2) 1,081 1,114 0,254 0,31 0,322 1,053 0,904 0,293 0,611 0,283 3,53E-04 C13(3) 1,351 0,898 0,260 0,32 0,318 1,008 0,928 0,292 0,636 0,283 3,53E-04 C15(1) 1,190 1,160 0,270 0,37 0,371 0,995 1,021 0,325 0,696 0,289 3,72E-04 C15(2) 0,870 1,410 0,263 0,323 0,330 1,023 0,923 0,303 0,620 0,293 3,84E-04 Microwave Devulcanization of Ground Tyre Rubber (GTR) 56 C15(3) 0,983 1,437 0,264 0,37 0,376 1,008 1,065 0,339 0,726 0,286 3,64E-04