Preparation Optimization Design of Tennis Ball Adhesive Formula Cai Yun-tao 1,a, Shi Bo-qiang 2, b,

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1 Applied Mechanics and Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Preparation Optimization Design of Tennis Ball Adhesive Formula Cai Yun-tao 1,a, Shi Bo-qiang 2, b, 1,2 P.E. Department, Hebei University of Science and Technology, China a @qq.com b shi1978@sohu.com Keywords: NR; tackifier; Tennis Abstract. The tennis ball adhesive formula is optimized by studying the impact of reinforcing system, tackifier, vulcanization system and solvent on the performance of NR-based tennis ball adhesive. The optimizing formula of rubber is: NR 100, Carbon Black N220 30, ZnO 8.3, Stearic Acid 2.2, Phenolic Tackifying Resin 3, Sulfur 3, Accelerator D0.5.The adhesive made through such optimizing formula shows good performance and the finished tennis ball has excellent adhesion and air tightness, satisfying the design requirements. Intorduction The excellent elasticity of tennis ball is provided by the internal air inflation. Therefore, air retaining of tennis ball is an important influencing factor of its performance, which is not only related with the air tightness of tennis ball bladder, but also closely related with the adhesion of tennis ball. The vulcanization of tennis ball is very unique. Firstly, it vulcanizes the rubber into two hemispheres and puts in inflating agent. Then, these two hemispheres will be bonded together for secondary vulcanization. This indicates that the bonding of tennis ball is the bonding between vulcanized rubbers, which is more difficult than that between unvulcanized rubbers. Therefore, firm adhesion requires experiment on the adhesive formula in order to gain qualified tennis ball adhesive. This paper optimized the tennis ball adhesive formula by studying the impact of reinforcing system, tackifier, vulcanization system and solvent on the performance of NR-based tennis ball adhesive. Experiment Main raw materials. NR, SIR20, Indonesia; Carbon Black N220 and N550, Tianjin Ebory Chemical CO., Ltd.; ZnO, stearic acid, Accelerator D/CZ and Sulfur, Shijiazhuang JiJing Chemical Tech co.,ltd.; Phenolic Tackifying Resin, Yuan Tai Biochemistry Co., Ltd.. Major equipments and instruments. XK-160 open mill, Shanghai Sinan Rubber Machinery Co.,Ltd.; GT-M2000 vulkameter and GT-AI-2000S tension tester, Gotech testing Machines Inc.; Plate vulcanization machine, Qingdao Yadong Machinery Group Co.,Ltd.; rubber thickness gauges, Shanghai Movie Machinery Factory. Sample preparation. Rubbers are mixed evenly on the open mill and then mill thinning for 6 times before unloaded. Some rubber compounds are vulcanized on the flat vulcanizing machine under the vulcanization condition of 145 t 90. The rest rubber compounds are dissolved in the solvent to make rubber adhesive for peeling test. The peeling test sample preparation: coat the rubber adhesive on two pieces of 180mm 11 mm vulcanized adhesive tapes evenly. The coating length is longer than 100mm. Bond them firmly and then put in the flat vulcanizing machine for vulcanization. Then, take it out for application. Performance test. All performances are tested according to corresponding national standards. Result and discussion Reinforcing system Fillers. The impact of different fillers on the adhesive performance is shown in Table 1. The vulcanized rubber filled with carbon black N220 has the maximum hardness, tensile strength and peel strength. The vulcanized rubber filled with white carbon black has the maximum tear strength. The reinforcement of carbon black N550 is between the carbon black N220 and the white All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,15:49:26)

2 934 Frontiers of Manufacturing Science and Measuring Technology III carbon black. The vulcanized rubber filled with nano calcium carbonate represents the poorest performance. This is because carbon black N220 can endow the vulcanized rubber good tensile property due to its higher structure. Given smooth particle surface, carbon black N550 is the furnace black with moderate reinforcement, poorer than carbon black N220. White carbon black enjoys higher reinforcement due to its large surface area and high activity. Therefore, the adhesive shall select carbon black N220 as the reinforcing filler. Table 1 The impact of different fillers on the adhesive performance Nano-CaCO_3 White Carbon Black Carbon Black N220 Carbon Black N550 t s2 /min t 90 /min Shore A hardness/ degree % stress at definite elongation/mpa Tensile strength/mpa Elongation at break/100% tear strength/(kn m -1 ) peel strength/( kn m -1 ) Note: The rest ingredients as well as their dosages of the formula are: NR 100, Filler 25, ZnO 8.3, Stearic Acid 2.2, Rosin 3, Accelerator CZ/D 1/1, Sulfur 4. Carbon black N220 dosage. The impact of carbon black N220 dosage on the adhesive performance is shown in Table 2. Table 2 The impact of carbon black N220 dosage on the adhesive performance carbon black N220 dosage/portion t s2 /min t 90 /min Shore A hardness/ degree % stress at definite elongation/mp a Tensile strength/mp a Elongation at break/100% tear strength/(kn m -1 ) peel strength/( kn m -1 ) Note: The rest ingredients as well as their dosages of the formula are: NR 100, ZnO 8.3, Stearic Acid 2.2, Rosin 3, Accelerator CZ/D 1/1, Sulfur 4. With the increasing dosage of carbon black N220, the hardness, 200% stress at definite elongation and tear strength of the vulcanized rubber increase, whereas the tensile strength and peel strength increase first and then decrease. The tensile strength and peel strength of the vulcanized rubber reach the peak at 20 and 30 carbon black N220 dosages, respectively. This is because increased carbon black dosage may strengthen its reinforcement on the rubber, thus improving the performances of vulcanized rubber. However, excessive carbon black dosage will decrease the rubber content and reduce the bonding points between rubber and the adherend, thus lowering the peel strength. Therefore, adhesive shall apply appropriate carbon black dosage as the reinforcing filler since excessive dosage may cause the rubber over solid, hardening and embrittlement, thus lowering its bond properties. Peel strength is an important property of adhesive. Hence, 30 carbon black N220 dosages are the optimal. Tackifier. Tackifier is mainly for increasing the viscosity of adhesive surface. Tackifier can increase the adhesive diffusibility and interaction between contact surfaces. The impact of different tackifiers on the adhesive performance is shown in Table 3. The 200% stress at definite elongation and peel strength of the vulcanized rubber can be increased by adding rosin, Coumarone-indene resin or phenolic resin. This indicates their good tackify effect to rubber. The vulcanized rubber added with phenolic resin represents the best performance. This is

3 Applied Mechanics and Materials Vols because resin molecules can penetrate into the rubber molecular chain, thus increasing the distance between rubber molecular chains and lowering the acting force between molecular chains. Therefore, rubber molecular chains are further activated and easy to diffuse, thus increasing the bond property. However, the poorer tackify effect of petroleum resin may be related with its molecular structure and rubber coating during bonding. To sum up, phenolic resin is the optimal tackifier of adhesive. Table 3 The impact of different tackifiers on the adhesive performance Blank Rosin Coumarone Resin Petroleum Resin Phenolic Tackifying Resin t s2 /min t 90 /min Shore A hardness/ degree % stress at definite elongation/mpa Tensile strength/mpa Elongation at break/100% tear strength/(kn m -1 ) peel strength/( kn m -1 ) Note: The rest ingredients as well as their dosages of the formula are: NR 100, Carbon Blank N220 30, ZnO 8.3, Stearic Acid 2.2, Tackifier 3, Accelerator CZ/D 1/1, Sulfur 4. Curing System Accelerator. The tennis ball bladder is bonded from two hemispheres, which is the bonding of two vulcanized rubbers. Therefore, unvulcanized rubber adhesive is filled in the bonding interface of vulcanized hemisphere before the vulcanization bonding. To ensure the inflating agent decomposed and inflated thoroughly, adhesive needs enough time to diffuse and penetrate on the bonding interface before the vulcanization reaction. Therefore, delayed accelerant CZ is applied and accelerant D is used for activation. The impact of accelerant CZ/D blending ratio on the adhesive performance is shown in Table 4. Table 4 The impact of accelerant CZ/D blending ratio on the adhesive performance accelerant CZ/D blending ratio 0.5/1 1/1 1.5/1 2/1 2.5/1 t s2 /min t 90 /min Shore A hardness/ degree % stress at definite elongation/mp a Tensile strength/mp a Elongation at break/100% tear strength/(kn m -1 ) peel strength/( kn m -1 ) Note: The rest ingredients as well as their dosages of the formula are: NR 100, Carbon Blank N220 30, ZnO 8.3, Stearic Acid 2.2, Phenolic Tackifying Resin 3, Sulfur 4. With the increasing of CZ/D blending ratio, the t s2 of the rubber generally prolongs, whereas t 90 shortens. The hardness, 200% stress at definite elongation and tear strength of the vulcanized rubber generally increase, whereas its tensile strength and peel strength increase first and then decrease. The peel strength and tensile strength of the vulcanized rubber reach the maximum value at 1.5/ 1 and 2/1 CZ/D blending ratio, respectively.as analyzed, this is because the CZ/D blending system can improve the cure degree of vulcanized rubber, thus enabling to produce products with good hardness, stress at definite elongation, tensile strength, elasticity and dynamic property. CZ and D activate the vulcanized rubber significantly at 1.5/ 1 and 2/1 CZ/D blending ratio, thus enabling the vulcanized rubber to achieve maximum peel strength and tensile strength. However, excessive accelerant dosages (CZ/D blending ratio >2/1) will increase the crosslinking density, hardness and brittleness of the vulcanized rubber, thus disadvantageous for bonding. Therefore, accelerant dosage shall be appropriate under the premise of rubber performance, optimally 1.5/1 CZ/D blending ratio.

4 936 Frontiers of Manufacturing Science and Measuring Technology III Sulfur. The impact of sulfur dosage on adhesive performance is shown in Table 5. It demonstrates that with the increasing dosage of sulfur, t s2 of the rubber changes slightly, whereas t 90 increases gradually. The hardness of vulcanized rubber generally increases, whereas its tensile strength and peel strength increase first and then decrease, which reach their peak at 3 sulfur dosages. As analyzed, increased sulfur dosage enables rubber to produce more cross bonds during vulcanization, thus increasing the crosslinking density and prolonging the curing time under same curing temperature. Furthermore, with the increasing dosage of sulfur, the stress at definite elongation and crosslinking density of the vulcanized rubber increase, thus increasing the cohesion. However, excessive sulfur dosages will result in excessive crosslinking density, thus resulting in reduced effective network chains and uneven load-bearing of network chains. Meanwhile, excessive crosslinking density is against diffusion, thus increasing brittleness but lowering the bond strength of the rubber. Therefore, excessive sulfur dosages (>3) will lower the tensile strength and peel strength of the vulcanized rubber. To sum up, 3 sulfur dosages are the optimal. Table 5 The impact of sulfur dosage on adhesive performance accelerant CZ/D blending ratio t s2 /min t 90 /min Shore A hardness/ degree % stress at definite elongation/mp a Tensile strength/mp a Elongation at break/100% tear strength/(kn m -1 ) peel strength/( kn m -1 ) Note: The rest ingredients as well as their dosages of the formula are: NR 100, Carbon Blank N220 30, ZnO 8.3, Stearic Acid 2.2, Phenolic Tackifying Resin 3, Accelerator CZ/D 1.5/1. Solvent. Rubber adhesive refers to the pulp made by dissolving rubber compounds into organic solvent. During the rubber dissolution, solvent molecules diffuse among rubber molecular chains and linear rubber molecules will absorb abundant solvent molecules, thus increasing their volumes as swelled. After a certain time, the space between rubber molecular chains increases, thus decreasing attraction between them and finally dissolved and dispersed in the solvent. Therefore, the intermiscibility between rubber and solvent, namely, the principle of similarity-intermiscibility, shall be taken into account when selecting solvent. The rubber compound (ingredients including: NR 100, Carbon Blank N220 30, ZnO 8.3, Stearic Acid 2.2, Phenolic Tackifying Resin 3, Accelerator CZ/D 1.5/1, Sulfur 3) is dissolved in toluene, gasoline and toluene/gasoline blending (volume ratio 1:1), respectively for rubber adhesive preparation. Their peel strengths are 6.7, 7.8 and 5.5 kn m -1, respectively, indicating that gasoline rubber adhesive has the best bonding effect, followed by toluene and toluene/gasoline blending successively. As analyzed, the solubility parameter of rubber is 7.9. According to the principle of similarity-intermiscibility, the closer the solubility parameter of rubber with that of solvent is, the better the intersolubility will be. This will result in distancing rubber molecular chains, obvious adhesive diffusion and penetration on two hemisphere interfaces of tennis ball, good interfacial layer structure and bond property, as well as high peel strength. Therefore, gasoline is the optimal solvent of adhesive. Summary The optimized tennis ball adhesive has good bond property and high strength. It not only can satisfy the tennis ball performance requirement, but also has good production and application value.

5 Applied Mechanics and Materials Vols References [1] Ma Hongxia, Li Yaocang, Research progress of new environment-friendly adhesives for pigment printing, China Adhesives.10(2010)47-50 [2] Tang Minghui, Lichao, In-situ preparation of precipitated silica/nr nano-composites, China Elastomerics. 04(2009)14-16

6 Frontiers of Manufacturing Science and Measuring Technology III / Preparation Optimization Design of Tennis Ball Adhesive Formula /