Effects of Running Shoes with Abrasion Resistant Rubber Sole on the Exercise Capacity of the Human Body

development of industrialization, rubber has been gradually used in the manufacture of sports equip- ment for its favourable properties. This study involved the addition of C5 petroleum resin into brominated isobutylene-isoprene rubber (BIIR) and butadiene rubber (BR) while manufacturing the sole of running shoes. The effects of running shoes with abrasion resistant rubber sole on the exercise capacity of

the development of industrialization, rubber has been gradually used in the manufacture of sports equip- ment for its favourable properties. This study involved the addition of C5 petroleum resin into brominated isobutylene-isoprene rubber (BIIR) and butadiene rubber (BR) while manufacturing the sole of running shoes. The effects of running shoes with abrasion resistant rubber sole on the exercise capacity of the human body were investigated by analysing the skid resistance and abrasion resistance of the running shoes, and conducting biomechanical study on naked feet and feet wearing the shoes. The results demonstrated that the rubber sole had favourable slip resistance property and mechanical properties such as stretching, abrasion resistance, and hardness. Compared to naked feet, the peak pressure intensity of the whole step of feet wearing the newly de- veloped shoes, was significantly lower than that of feet wearing ordinary shoes. In the future, rubber can bring more comfortable experience because of its favourable properties. Keywords Rubber shoes, performance analysis of rubber sole, biomechanics * Corresponding author: Bo Wang, B. A. e-mail: wnbo_123@sina.com

B. WANG: Effects of Running Shoes with Abrasion Resistant Rubber Sole on the…, Kem. Ind. 66 (9-10) (2017) 525−530526 With the development of industry, rubber materials have been gradually applied in running shoes and studies on rubber running shoes are constantly expanding. N. J. Mills found that the design of even appearance could provide a buffer for feet and the shoes made of rubber were more durable. 8 Through investigating the buffer, tractive force and flexibility of running shoes, K. Harano found that the running shoes made of rubber could improve the comfort of running shoes and athletic ability of the human body by effectively enhancing those characteristics. 2.2 Manufacture of running shoes sole and experimental methods The materials included BIIR (Chengdu Xinlongda Rubber Products Co., Ltd., China), BR (Chengdu Xinlongda Rubber Products Co., Ltd., China), C5 petroleum resin (Chengdu Tianli Hongyuan Chemical Co., Ltd., China), white carbon black 10 (Chengdu Runze Bentu Chemical Co., Ltd., China), accelerant (Chengdu Hanhua New Material Science and Technology Co., Ltd., China), zinc oxide (Chengdu Run- ze Bentu Chemical Co., Ltd., China), paraffin oil (Cheng- du Xinhua Petroleum and Chemical (Commercial) Co., Ltd., China) and sulphur (Chengdu Xinhua Petroleum and Chemical (Commercial) Co., Ltd., China). The manufacturing tools included twin-roll mixing mill (XK-450, Qingdao Qingxiang Mechanical Co., Ltd., Chi- na), vulkameter (CL-2000E, Yangzhou Jingzhuo Testing Machinery Factory, China), Mooney viscometer (JZ-6028, Yangzhou Jingzhuo Testing Machinery Factory, China), dy- namic thermomechanical analysis apparatus (DMA-8000, Perkin Elmer Co., Ltd., USA), plate vulcanizer (SY-6210-A, Dongguan Shiyan Precise Instrument Co., Ltd., China), hardness tester (HRD-150T, Shanghai Jujing Precise In- strument Manufacture Co., Ltd., China), electric tension tester (TFW-5S, Shanghai Tuofeng Instrument Science and Technology Co., Ltd., China), abrasion machine (H-X626, Yangzhou Huahui Detection Instrument Co., Ltd., China), impact elasticity tester (CMT1000, Zhuhai Sansi Taijie Elec- trical Equipment Co., Ltd., China), and slip tester (QI-009, Dongguan Houjie Kailan Detection Instrument Factory, China). Manufacturing process was as follows: (1) BIIR and BR were mixed in a ratio of 3 : 7 after five mill runs. (2) C5 was added, followed by white carbon black. (3) After five minutes of mixing,

elasticity tester (CMT1000, Zhuhai Sansi Taijie Elec- trical Equipment Co., Ltd., China), and slip tester (QI-009, Dongguan Houjie Kailan Detection Instrument Factory, China). Manufacturing process was as follows: (1) BIIR and BR were mixed in a ratio of 3 : 7 after five mill runs. (2) C5 was added, followed by white carbon black. (3) After five minutes of mixing, accelerant and com- pounding agents such as zinc oxide were added. (4) After mixing, paraffin oil and sulphur were added. (5) The rubber was covered along the opposite direction of roller motion five times and processed by sheeting. (6) After material configuration, it was put aside for 24 h. (7) The vulcanization and Mooney viscosity of the material were tested using the vulkameter and Mooney viscom- eter. (8) It was vulcanized by the plate vulcanizer according to the test results. After the manufacture of the sample, a performance test was performed to determine whether the sample is quali- fied for the sole of running shoes. (1) The sulphuration of the sample was tested on an M-2000-FA vulkameter at a temperature of 150 °C ac- cording to AMD5289-95 standard. (2) Mooney viscosity test was performed on a GT-7080S2 Mooney viscometer according to ASTMD1646-99 standard. It was preheated by a small rotor at 100 °C for 1 min, and the test lasted 4 min. (3) The hardness of the sample was tested using a hardness tester according to ASTMD2240:2005 standard. (4) Tensile strength and tearing strength were tested us- ing an electronic tensile machine according to AST- MD412:1998 and TSAMD642:2000 standards. (5) The abrasion of the sample was tested using an abra- sion test machine according to GB9867-2008 stand- ard. (6) The slip resistance of the sample was tested using a slip resistance test machine according to TM 144 stand- ard. 2.3 Plantar pressure test Plantar pressure test was performed using an insole plantar pressure test system. 2.3.1 Selection of subjects In this study, tested were athletes wearing the test shoes with the sample sole, shoes purchased on the market with soles made of ethylene-vinyl acetate copolymer (EVA) foamed material (control shoes),

resistance test machine according to TM 144 stand- ard. 2.3 Plantar pressure test Plantar pressure test was performed using an insole plantar pressure test system. 2.3.1 Selection of subjects In this study, tested were athletes wearing the test shoes with the sample sole, shoes purchased on the market with soles made of ethylene-vinyl acetate copolymer (EVA) foamed material (control shoes), and those with no shoes. In the BIIR, which was used for manufacturing the exper- imental shoes, the dosage of C5 was 10 phr, the tensile strength was 17.4 MPa, and the elongation at break of cells was 690 %, suggesting a good molecular structure. EVA foamed material, which was used for manufacturing the control shoes, was composed of ethylene and vinyl ace- tate, and its content was 14 % – 30 %; the shoes were or- dinary brand shoes. The athletes selected were those who had done running exercise for more than one year, ran no less than 10 km every week, had no injury on the lower limbs in the last six months, and did no intense exercise within 48 h before the test. 2.3.2 Partition of plantar pressure The human plantar was divided into different parts during pressure test. The pressure data were recorded. The plan- tar pressure partition is shown in Fig. 1.

B. WANG: Effects of Running Shoes with Abrasion Resistant Rubber Sole on the…, Kem. Ind. 66 (9-10) (2017) 525−530 527 A B CDE H I J F G Fig. 1–Partition of plantar pressure A stands for the first phalanx, B stands for the second to fifth phalanx, C, D, E, F and G stand for the first, second, third, fourth, and fifth metatarsal bone, respectively, H stands for arch, I stands for the inner side of heel, and J stands for the outer side of heel. 2.3.3 Test process The plantar pressure data of the right foot were collected, and the sampling frequency was set as 100 Hz. Before the test, the athletes wore test equipment and plantar pres- sure data acquisition box; system zero adjustment was per- formed. Moreover, the athletes were asked to be familiar with the sports platform. After preparation, the athletes were asked to run on the sports platform at a speed of 3 m s −1 . After 20 s of uniform motion, the plantar pressure data of the athletes were col- lected. The data for the athletes wearing the test shoes, control shoes, and no shoes were all recorded. At the end, the athletes walked on the sports platform at a speed of 1.5 m s −1 , and the other conditions remained the same; the pressure data were collected. 3 Results and discussion 3.1 Vulcanization and Mooney properties The vulcanization degree of the manufactured samples was different due to different dosage of C5. The vulcaniza- tion parameters of the sample are shown in Table 1. The experimental results are shown in Table 1. With the increase in dosage of C5, the initial torque and maximum torque of the sample and torque difference decreased gradually, and the scorch time and optimum cure time extended. This indicated that the addition of C5 could reduce the crosslinking of rubber and viscosity of rubber compound; moreover, the gap between molecule seg- ments became larger, which led to the decrease in con- centration of vulcanizing agent and accelerator, and ex- tended the curing time. With the increase in

gradually, and the scorch time and optimum cure time extended. This indicated that the addition of C5 could reduce the crosslinking of rubber and viscosity of rubber compound; moreover, the gap between molecule seg- ments became larger, which led to the decrease in con- centration of vulcanizing agent and accelerator, and ex- tended the curing time. With the increase in curing time, the initial torque and maximum torque decreased stead- ily, suggesting that the curing time had no influence on vulcanization flatness. With the increase in C5 dosage, the Mooney viscosity of the sole material greatly decreased firstly, and then tended to be stable, as shown in Fig. 1. As C5 resin acted as a sof- tener in the process of sulphuration, the molecular weight and torque of the material decreased, leading to the de- crease in Mooney viscosity. 11 When the dosage of C5 resin became saturated, it acted as filler in rubber compound and would not reduce the viscosity of the material. There- fore, when the dosage of C5 exceeded 10 phr, the Mooney viscosity tended to be stable. Table 1 – Vulcanization parameters of the material Dosage of C5 ⁄ phr Scorch time ⁄ min Optimum cure time ⁄ min Initial torque ⁄ dN m Maximum torque ⁄ dN m Torque difference ⁄ dN m 0 2.5 5.9 9.1 32.6 23.4 5 2.1 5.7 7.0 27.4 20.2 10 2.9 5.9 6.6 22.4 14.5 15 3.3 6.6 6.4 20.2 12.7 25 2.6 6.8 5.1 17.4 10.6

B. WANG: Effects of Running Shoes with Abrasion Resistant Rubber Sole on the…, Kem. Ind. 66 (9-10) (2017) 525−530528 3.2 Analysis on slip resistance and mechanical properties Table 2 suggests that the wet slip resistance of the forefoot, smooth and heal increased with the increase in C5 dos- age, indicating that the addition of C5 could significantly improve the wet slip resistance of the materials. As to dry slip resistance coefficient, the slip resistance coefficients of the forefoot, smooth and heal changed slightly, suggesting that the addition of C5 had little influence on the wet slip resistance of the material. With the increase in C5 dosage, DIN abrasion had little changes in the earlier stage, 12 but showed a sharp increase when the dosage of C5 exceeded 15 phr. This was be- cause the short chain of C5, which combined with the macromolecule segment, reduced the degree of freedom of rubber, improved the temperature of transforming to vitrification, and increased the crosslinking between the rubbers. 13 When the dosage of C5 was no more than 15 phr, the influence on the DIN abrasion of the material was low. Table 2 demonstrates that the tensile strength of the ma- terial increased firstly and then decreased, and the elon- gation at break improved constantly with the increase in C5 dosage. This was because the filler and compounding agents gradually dispersed with the increase in C5 dosage, leading to the interfacial compatibility of the material and the improvement of bonding strength between the rub- bers. When the dosage of C5 exceeded 15 phr, the adhe - sion between the two rubbers decreased, and the interac- tion between the filler and the matrix weakened, leading to the decrease in tensile strength. This was because the addition of C5 improved the action ca- pacity of molecular segment, the relative slippage between molecular segment and the activity of crosslinked network, leading to the enhancement of elongation at break. It could be concluded from Table 2 and Fig. 1 that the ad - dition of C5 changed the crosslinking density and torque of the material, and consequently

the addition of C5 improved the action ca- pacity of molecular segment, the relative slippage between molecular segment and the activity of crosslinked network, leading to the enhancement of elongation at break. It could be concluded from Table 2 and Fig. 1 that the ad - dition of C5 changed the crosslinking density and torque of the material, and consequently the hardness and impact resilience decreased with the increase in C5 dosage. The decrease in impact resilience suggested the enhancement of shock resistance of the material. Table 2 – Influence of C5 dosage on the slip resistance coefficient and mechanical properties C5 dosage ⁄ phr Tensile strength ⁄ MPa Hardness (Shore A) DIN abrasion ⁄ mm 3 Slip resistance coefficient (dry)Slip resistance coefficient (wet) forefootsmooth heel forefootsmooth heel 0 14 71.2 97.2 1.14 0.96 0.79 0.47 0.46 0.43 5 16.2 65.8 99.7 1.09 1.07 0.87 0.49 0.52 0.46 10 17.4 62.3 99.5 1.1 1.06 0.83 0.5 0.55 0.47 15 17.5 59.7 100.1 1.14 1.08 0.79 0.53 0.6 0.5 20 14.3 53.7 112.3 1.03 1.07 0.85 0.55 0.67 0.52 0 5 10 15 20 25 30 elongation at break ⁄ % impact resilience ⁄ % C5 dosage ⁄ phr elongation at break impact resilience 0 100 200 300 400 500 600 700 800 900 0 0 10 15 20 25 30 Fig. 3–Influence of dosage of C5 on the elongation at break and impact resilience 0 20 40 60 80 100 120 0 5 10 15 20 25 C5 dosage ⁄ phr Money viscosity Fig. 2–Influence of C5 dosage on the Mooney viscosity

B. WANG: Effects of Running Shoes with Abrasion Resistant Rubber Sole on the…, Kem. Ind. 66 (9-10) (2017) 525−530 529 3.3 Pressure test on rubber sole, naked feet, and ordinary sole The peak pressure is shown in Fig. 4. 5 10 15 20 250 A B C D E F G H I A B C D E F G H I J J peak pressure ⁄ kPa Peak plantar pressure when walking Peak plantar pressure when jogging peak pressure ⁄ kPa division of planta pedis division of planta pedis testing shoes ordinary running shoes naked feet testing shoes ordinary running shoes naked feet 05101520253035404550 Fig. 4–Peak plantar pressure when walking and jogging Fig. 4 demonstrates that the peak plantar pressure of feet wearing shoes when walking was obviously lower than that of naked feet; the position with high plantar pressure pre- viously had significantly pressure. It could be concluded that by wearing the running shoes excessive pressure and generation of local pain could be avoided, and comfort during walking improved. The pressure on the feet wearing the test shoes was distrib- uted more evenly compared to ordinary shoes. Except the first metatarsal bone whose pressure had slightly increases, the pressure of the other parts had remarkably reduced. This indicated that the sole, which was made of BIIR and BR, could more effectively reduce plantar pressure and im- prove comfort. 4 Conclusion This study investigated the properties of BIIR and BR, and developed the sole of running shoes with BIIR, BR, and C5 petroleum resin. Experiments were carried out to prove that the rubber could improve the strength, hardness, ten- sile strength, and abrasion resistance of running shoes soles. The exercise test suggested that the shoes could effectively reduce plantar pressure and enhance comfort. This work provides a reference for the manufacture of running shoes with rubber. List of abbreviations and symbols BIIR– brominated isobutylene-isoprene rubber BR – butadiene rubber EVA– ethylene-vinyl acetate phr– parts per hundred rubber References Literatura 1. K. Pyo, J. Choi, J. Lee, C. Park, Improvement of Frictional Property of BR/CIIR Composite Rubber for Shoes Out-

pressure and enhance comfort. This work provides a reference for the manufacture of running shoes with rubber. List of abbreviations and symbols BIIR– brominated isobutylene-isoprene rubber BR – butadiene rubber EVA– ethylene-vinyl acetate phr– parts per hundred rubber References Literatura 1. K. Pyo, J. Choi, J. Lee, C. Park, Improvement of Frictional Property of BR/CIIR Composite Rubber for Shoes Out- sole, Polym. Korea 37 (3) (2013) 255–261, doi: https:// doi.org/10.7317/pk.2013.37.3.255. 2. Y. Wang, W. Y. Zhou, L. Li, A. M. Zhang, SEBS modified reclaimed rubber microcellular foaming material as the sole of the shoe, Polym. Mater. Sci. Eng. 26 (12) (2010) 148–151, url: http://caod.oriprobe.com/articles/25909767/ SEBS_Modified_Reclaimed_Rubber_Microcellular_Foami. htm. 3. Y. Zhang, S. X. Li, W. L. Guo, Z. W. Deng, The Effects of Bromination Condition on the Microstructure of Bromi- nated Butyl Rubber, J. Petrochem. Univ. 23 (1) (2010) 27–29, url: http://en.cnki.com.cn/Article_en/CJFDTo- tal-SYHX201001007.htm. 4. X. Yang, Y. Zhang, Y. Xu, S. Gao, S. Guo, Effect of octadec- ylamine modified graphene on thermal stability, mechan- ical properties and gas barrier properties of brominated butyl rubber, Macromol. Res. 25 (3) (2017) 270–275, doi: https://doi.org/10.1007/s13233-017-5035-7. 5. C. A. D. Silva, H. Budde, M. Menzel, U. Wendler, M. Bart- ke, M. Weydert, M. Beiner, Self-assembled structure and relaxation dynamics of diblock copolymers made of po- lybutadiene and styrene/butadiene rubber, RSC Adv. 6 (56) (2016) 50460–50470, doi: https://doi.org/10.1039/ C6RA06786G. 6. S. S. Choi, K. H. Chung, C. Nah, Improvement of prop- erties of silica-filled styrene-butadiene rubber (SBR) compounds using acrylonitrile-styrene-butadiene rubber (NSBR), Polym. Adv. Technol. 14 (8) (2010) 557–564, doi: https://doi.org/10.1002/pat.367. 7. J. Liang, S. Chang, N. Feng, Effect of C5 petroleum resin content on damping behavior, morphology, and mechan- ical properties of BIIR/BR vulcanizates, J. Appl. Polym. Sci. 130 (1) (2013) 510–515, doi: https://doi.org/10.1002/ app.39202. 8. N. J. Mills, Chapter 13-Running shoe case study, in Poly- mer Foams Handbook, 2007, pp. 307–327, doi: https:// doi.org/10.1016/B978-075068069-1/50014-3. 9. K. Harano, The Athletic Shoes, Nippon Gomu Kyokai- shi 83 (5) (2010) 133–137, doi: https://doi.org/10.2324/ gomu.83.133. 10. A. F. Plante, C. Peltre, J. Chan, T. Baumgartl, P. Erskine, M. Apesteguía, I. Virto, Green Carbon, Black Carbon, White Carbon: Simultaneous Differentiation

The study investigates the effects of rubber soles on exercise capacity.