Butyl Reclaim in Innerliner Applications 1

ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS Butyl reclaim Innerliner Better processing Improved performance Reclaimed butyl rubber is an important compounding ingredient that is widely used in the tire industry. For innerliner applications halobutyl compounds are used for which partial replacement with butyl reclaim is possible. An increasing amount of butyl reclaim results in a lower air permeability enabling the manufacturer to reduce the thickness of the innerliner. Aging resistance of the compound is also improved; in particular the flex fatigue life after aging is increased considerably. The most significant processing improvement is better air venting during tire construction and curing. The results of a thorough investigation of increased butyl reclaim loading on the overall properties of various butyl compounds and halobutyl compounds will be discussed. Butylregenerat in Innerlinermischungen Butylregenerat Innerliner Bessere Verarbeitung und Eigenschaften Butylregenerat ist ein wichtiger Mischungsbestandteil fuè r die Reifenindustrie. FuÈ r Innerlinermischungen werden Halobutyl-Mischungen eingesetzt. Ein Teil des Halobutylkautschuks kann durch Regenerat ersetzt werden. Mit steigenden Mengen Butylregenerat erzielt man eine geringere GasdurchlaÈ ssigkeit und gestattet damit eine Reduktion der StaÈ rke des Innerliners. Auch erzielt man ein besseres Alterungsverhalten sowie ein geringeres Flexcracking nach Alterung. WaÈ hrend der Vulkanisation werden LufteinschluÈ sse zwischen Bladder und Innerliner durch steigende Mengen Butylregenerat verringert. Die Ergebnisse einer eingehenden Untersuchung uè ber den Einfluû von steigenden Mengen Butylregenerat in Butyl-Mischungen und Halobutyl- Mischungen werden diskutiert. Butyl Reclaim in Innerliner Applications 1 H.-J. Manuel, W. Dierkes and A. Hendriks, Maastricht (NL) Butyl rubber reclaim produced from scrap rubber materials can be used in a number of rubber compounds that use the visco-elastic nature of the reclaim to impart rubbery properties and good physical properties. Butyl rubber reclaim was introduced shortly after large scale production of regular butyl rubber commenced in the 1940's. Raw materials used for feeding the reclaiming process mainly are based on inner tubes, as these are most easily handled and in great supply. In the early days the butyl rubber was reclaimed with pan-heater processes. Here the material was ground, mixed with swelling oils and possibly reclaiming oils and heated for several hours in steam pressurised autoclaves. It was then refined on large mills and strained through extruders equipped with screens to remove contamination. Drawbacks on this process, still used in some Asian and South American countries, are the batch production and the difficulty to control the reaction thoroughly. Especially oxidation due to high temperatures is seen to decrease physical properties such as the tensile strength of the reclaim. Developments on this process were made by using high speed autoclaves reducing the reaction times to minutes and being able to control the reaction more thorough. However, the drawback of having a batch wise fluctuation is not eliminated with these developments. A continuous system was developed in the 1950's and was based on extruder equipment. One of its greatest assets 1) Presented at a meeting of the Rubber Division, American Chemical Society Orlando, Florida, September 21±24, 1999 was the reduction of fluctuations as experienced in batch productions. Further to that the process gives a much better processing control and the ability to automatise. This thermo-mechanical process [1 ± 3] is used by Vredestein in Maastricht. Here the scrap materials are cut, washed, separated from valves, cut again and fed to the extruder section. Without the aid of any chemicals the material is reclaimed through shear and heat. Finally, two straining and one refining step ensure the end product to be smooth and homogeneous. Recent developments on this process have focussed on improvements in the refining section, the lay out of the extruder and screw geometry and improvements in the analysis of the raw materials thus reducing fluctuating factors. The result is a highly consistent material with physical properties close to the original materials (as can be seen in the results displayed in this article). Experimental Testing of the material The butyl rubber reclaim is tested in two different innerliner compounds based on bromobutyl rubber and a blend of chlorobutyl with natural rubber. The butyl rubber reclaim was tested in these compounds, due to the noted good properties of the halobutyl polymer [4] and the trend to increase this amount in innerliners [5 ± 7]. A third test compound is based on regular butylrubber. The test recipes are provided in Tab. 1. The compound is mixed in a two-step process using a 2,5 liter Banbury mixer. The mixing conditions are provided in table 1. Reclaim is added on top of the original compound with the curing additives 730 KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 12/2000

Table 1. Butyl rubber test recipes Bromobutyl compound Chlorobutyl/NR compound Butyl compound Step 1: Maximum mixing temperature: 135 8C 135 8C 160 8C BIIR 100.00 CIIR 70.00 IIR 100.00 CB N660 60.00 SMR 20 30.00 CB N375 55.00 Koresin resin 4.00 CB N660 60.00 Par.oil 25.00 Struktol 40MS 7.00 Koresin resin 4.00 Stearic acid 1.00 Par. Oil 8.00 Struktol 40MS 7.00 Zinc oxide 5.00 Stearic acid 2.00 Par. Oil 8.00 ODPA 1.00 Maglite D 0.15 Stearic acid 2.00 MBTS 1.50 Step 2: Maximum mixing temperature: 90 8C 90 8C 100 8C Zinc oxide 3.00 Zinc oxide 3.00 MBTS 0.50 Sulphur 0.50 MBTS 1.50 TMTD 1.00 Sulphur 0.50 Sulphur 1.75 adjusted to compensate for the increased polymer content. Tab. 2 lists the different test methods used to analyse the influence of butyl rubber reclaim on the properties. Mooney viscosity (Monsanto Mooney 1500S) and rheometer curve (Monsanto 100S, ODR type at 160 8C) were determined to indicate processing properties. The green strength is determined by stretching unvulcanized test bars towards breaking or the end of the test zone and measuring the peak value in the stress strain curve. After vulcanization of the compounds moduli, tensile strength, elongation at break and tear strength are determined on a Monsanto tensometer 10. These physical properties are also measured after aging the tensile bars for 72 h at 125 8C in a circulating hot air oven. Hardness was tested with a Frank Shore A hardness tester. After aging the material for 168 h at 120 8C in a circulating hot air oven flex life was determined with a DeMattia flex tester. Permeability was measured according to ISO 2782. Test pieces with a thickness of 0.8 mm are measured at 65 8C with procedure B, vertical capillary tube method, at 5 bar pressure difference. Results and discussion Butyl reclaim in inner liner compounds based on bromobutyl rubber and based on 70 phr chlorobutyl and 30 phr natural rubber Influence on processing behavior The curing characteristics of the compound are influenced by the addition of reclaim: scorch time is reduced by approximately two seconds per phr reclaim added to the compound. The curing time is not influenced. It should be noted that no changes were made to the curing system in order to adjust the scorch time for the purposes of this test. If desired, the scorch time can be influenced by a variation in the sulfur/ accelerator ratio. Table 2. Test methods Mooney viscosity ASTM D1646 Curing behavior ODR, 160 8C, arc. 3 Modulus Tensile strength ASTM D412 Elongation at break Hardness (Shore A) ASTM D2240 Tear strength [N] ISO 816 (Delft) Flex fatigue resistance ISO 132 (De Mattia) Permeability Calculated (65 8C, 149 8F) DIN 53536 Fig. 1 to 7 provides an overview of the influence of butyl rubber reclaim on the properties of an innerliner compound based on 100 phr bromobutyl rubber and of an innerliner compound based on 70 phr chlorobutyl and 30 phr natural rubber. For the bromobutyl compound the green strength increases while for the chlorobutyl/natural rubber compound it slightly decreases. But as the green strength of the chlorobutyl/natural rubber compound is relatively high, also due to the addition of 30 phr natural rubber, this should not cause a problem. From experiments with other types of reclaim and practical experiences it is known that the processing behaviour of compounds with reclaim improves. Calander shrinkage and extrusion die swell are reported to decrease. This probably is caused by the fact that the reclaim partly is comparable to a pre-crosslinked rubber, which is often used to improve on processing behaviour. Influence on the physical properties of the compound For the chlorobutyl/natural rubber based compound the modulus and tensile strength are reduced with the introduction of small amounts of reclaim. The addition of higher concentrations does not result in a further reduction of these properties. Elongation at break is increased, similar to the effect on tensile strength: a significant increase for small loadings, and reaching a plateau for higher loadings. For the bromobutyl based compound the modulus, tensile strength and elongation at break are not influenced. Important improvements for the bromobutyl compound as a result of the addition of butyl rubber reclaim includes an increase in tear strength and decrease in air permeability. An approximately 6 % improvement in permeability for a reclaim loading of 30 phr was noted. For the chlorobutyl/natural rubber compound tear strength is reduced but air permeability is influenced positively in the same order of magnitude as for the bromobutyl compound. During adhesion measurements of the bromobutyl compound, no separation of the rubber and fabric was observed, indicating that the bonding strength to fabric KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 12/2000 731

Fig. 1. The influence of butyl rubber reclaim on the Green Strength of halogenated innerliner compounds Fig. 2. The influence of butyl rubber reclaim on the modulus at 300 % of halogenated innerliner compounds Fig. 3. The influence of butyl rubber reclaim on the Tensile Strength of halogenated innerliner compounds Fig. 4. The influence of butyl rubber reclaim on the Elongation at break of halogenated innerliner compounds Fig. 5. The influence of butyl rubber reclaim on the Tear Strength of halogenated innerliner compounds Fig. 6. The influence of butyl rubber reclaim on the adhesion of halogenated innerliner compounds 732 KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 12/2000

(canvas) is higher than the internal strength of the rubber. For the chlorobutyl/natural rubber based compound adhesion to the carcass is slightly improved. Fig. 7. The influence of butyl rubber reclaim on the Permeability of halogenated innerliner compounds Aging behavior of the bromobutyl compound is improved by the addition of reclaim (Fig. 8): the greater amount of reclaim which is loaded, the smaller the reduction in tensile strength and elongation at break after aging. No influence on tear strength is found. The aging of the chlorobutyl/natural rubber compound is improved in terms of tensile strength, elongation at break and tear strength (Fig. 10). The improvements are less pronounced when compared to the bromobutyl compound. For both compounds the most important improvement is the increase in flex fatique resistance as can be seen in Fig. 9 and 11. Flex life is determined after aging for 168 h at 120 8C. In addition to the influence on physical properties, an influence on raw material costs is found (Fig. 12). For both compounds the addition of 10 phr butyl rubber reclaim results in a cost reduction of one percent, based on current Western European prices for the ingredients used in the compounds. Fig. 8. The influence of butyl rubber reclaim on the aging properties of a bromobutyl rubber compound; Aging conditions: GE, 125 8C, 72 h Fig. 9. The influence of butyl rubber reclaim on the flex fatigue resistance of a bromobutyl compound after aging; Aging conditions: GE, 120 8C, 168 h Fig. 10. The influence of butyl rubber reclaim on the aging properties of a chlorobutyl/natural rubber compound; Aging compounds: GE, 125 8C, 72 h Fig. 11. The influence of butyl rubber reclaim on the flex fatigue resistance of a chlorobutyl/natural rubber compound after aging; Aging conditions: GE, 120 8C, 168 h KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 12/2000 733

Butyl reclaim in a compound based on regular butyl rubber Influence on processing behavior The curing characteristic of the compound is influenced by the replacement of 20 phr butyl rubber with the same amount of recycled butyl rubber. A longer scorch time and curing time are found in the compound containing reclaim. The compound viscosity is not influenced. Influence on the physical properties of the compound No influence is found for modulus (300 %), hardness or tear strength. Tensile strength and elongation at break are slightly reduced (Tab. 3). The overall aging properties are improved as can be seen in Tab. 4. Less influence of the aging process is found in the case of tensile strength, elongation at break and hardness. Conclusions Fig. 12. Influence of butyl rubber reclaim on the price of halobutyl compound The introduction of butyl rubber reclaim in halobutyl innerliner compounds results in significant improvement in processing behavior and in the performance of this compound. The most important properties of an innerliner such as impermeability, aging resistance in general and flex fatigue resistance after aging in particular are improved. The reduction in permeability allows a parallel reduction of the innerliner thickness, with positive influence on tire weight and on raw material costs. The total price reduction can reach nearly ten percent in the case of a compound loaded with 30 phr of reclaim. That butyl rubber reclaim is a valuable raw material in inner liner compounding is evidenced by the fact that it is utilized by most tire manufacturers. Table 3. The influence of butyl rubber reclaim on the properties of a regular butyl rubber compound Property Relative value of the property (%) Scorch time 105 Curing time 121 Mooney viscosity 98 Modulus 300 % 105 Tensile strength 89 Elongation at break 94 Hardness Shore A 98 Tear strength 100 Permeability 96 Compound of the results above: 80 phr IIR and 36 phr butyl rubber reclaim. Compound with 100 phr IIR and 0 phr reclaim: relative value of the properties is 100 % Table 4. The influence of butyl rubber reclaim on the aging properties of a regular butyl rubber compound. Aging conditions: 100 8C, 14 days Property Relative value of the property after aging (%) (Before aging: 100 %) 100 phr IIR 80 phr IIR 0 phr reclaim 36 phr reclaim Tensile strength 80 83 Elongation at 60 65 break Hardness Shore A 111 109 Tear strength 60 65 In a follow-up study the effect of high filler loadings is also studied, to look at compounds with better property/price performance [8]. References [1] H.J. Manuel, Nat. Rubber Conf., Natal Drakensberg, South Africa, Oct. 15±16 (1999). [2] W. Dierkes, Tire Technology Int. '98, 170±175 (1998). [3] H.J. Manuel and W. Dierkes, Rapra Review Report on Recycling of Rubber Vol. 9, report 99 (1997). [4] Bayer AG, Handbuch fuer die Gummi-Industrie, Guetersloher Druckservice GmbH, Guetersloh, 2nd ed. (1991). [5] A.J.M. Sumner, TyreTech '98, London, June 15 ± 16 (1998), paper 3. [6] A.J.M. Sumner and S.R. Haigh, proceedings of Int. Rubber Conf., Seoul, Korea, April 25 ±29 (1999), 163 ±169. [7] T.A. Mills, Nat. Rubber, Conf., Durban, South Africa, Oct. (1997). [8] H.J. Manuel, ACS-Rubber Division, Dallas, 4±6 April (2000), paper 62. The authors Henk-Jan Manuel is Manager R&D at Vredestein Rubber Resources BV. Anita Hendriks is R&D Officer at Vredestein Rubber Resources. Wilma Dierkes was with Vredestein Rubber Resources until spring 1999 as Manager Product Application Development. Corresponding author: Mr. Henk-Jan Manuel Vredestein Rubber Resources B.V. Lage Frontweg 2a NL-6200 AK Maastricht 734 KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 12/2000