The utilization of waste fibers represents an important environmental benefit and great economic savings for the community. In this study short nylon fibers waste was modified with Glycidyl 3-Pentadecenyl Phenyl Ether (GPPE) in the presence of Triethylamine/Ammonium persulfate by a simple two-step procedure. The reinforcing effects of modified fibers (MNSF-2) on the vulcanization characteristics, mechanical properties, dynamic mechanical properties, and the wear resistant property of Styrene Butadiene Rubber (SBR) tread compounds were investigated. The addition of the MNSF-2 resulted in slightly lower minimum torque (
Short fibers/rubber composites exhibit combined behaviors of the soft and elastic rubber matrix as well as stiff and strong fibrous reinforcement. These composites have been successfully used in production of V-belts, hoses, tire treads, and complex shaped mechanical goods [
Fiber-matrix adhesion in short fiber-rubber composites has been a field of extensive researches [
In engineered truck tread compounds, a low content of well dispersed short fibers is usually introduced to improve mechanical and dynamic properties [
Rubber elasticity is essential for many important tire properties such as wet traction performance [
Nowadays, Management of End-of-Life Tires has become a critical problem worldwide. During the process of tire recycling, approximately 10% of waste short fibers which mainly consist of nylon, polyester, or cellulose are obtained [
Our previous research results had confirmed that short nylon fibers waste maintained their length upon mixing and had reinforcing effects on Ethylene Propylene Diene Monomer rubber [
The molecule structure of GPPE.
In this study we utilized GPPE to modified short nylon fibers waste to form adequate interfacial bonding between fibers and rubber matrix for obtaining high-performance tread compound. The reference compound used is a typical tire tread composition consisting of SBR matrix and the key ingredients. The modified method and the fibers contents on the properties of SBR tread compound were investigated.
Short nylon fibers waste with 0.5~2 cm length and 15~45
AA and APS were dissolved in purified water at certain ratio, stirring dispersion at 25°C for 1 hour to obtain fully mixed solution A. GPPE, TEA, and OP-10 were mixed in purified water, stirring at 25°C for 20min to prepare solution B.
A simple two-step method was used to modify fibers. In the first step, solution A was sprayed into short nylon fibers waste which was predispersing in a high-speed mixer at 1400r/min speed for 20min. Subsequently the resultant fibers were taken out and placed into a vacuum oven at 70°C for 2.5 hours to obtain the pretreated fibers (marked as MNSF-1). In the second step, MNSF-1 was mixed with solution B following the procedure similar to the first step to obtain the modified fiber (marked as MSNF-2). MSNF-2 was used in the rubber tread compound formula.
The modified fiber was dipped into ethyl alcohol for 12 hours then washed by deionized water several times to remove the unreacted monomer. After vacuum dried at 90°C for 24 hours, the purified fiber was characterized by FTIR and SEM.
The formulation of the compounds was as follows (parts per hundred rubber, phr): 100 phr SBR, 5 phr zinc oxid, 1.5 phr stearic acid, 1.5 phr N-cyclohexyl-N-phenyl-p-phenylenediamine, 1.8 phr N-cyclohexyl-2-benzothiazole sulfonamide, 35 phr carbon black (N330), 35 phr silica, 25 phr aromatic oil, and 2 phr sulphur. Various short fibers with different contents were compared in the formulation.
Mixing was carried out in a laboratory two-roll mill (150×300mm) at a friction ratio of 1:1.2 according to ASTM standard D 3184-80. The roll temperature was kept at about 50°C during mixing. SBR was masticated on the mill for 2 min, followed by the addition of ingredients except fibers. Fibers were added at the end of the mixing process. We added the fibers evenly to the batch and passed the batch through the mill at a nip of 2 mm continuously for 2 min, then removed the batch from the mill. Subsequently the batch was passed through the mill five times at a nip of 1mm, folding it back on itself each time. We were paying attention to maintain approximately uniform orientation of fibers in the calender direction of mill and making sure most fibers were aligned in the same direction. Afterward the master batch was sheeted out to 2 mm thickness for the vulcanization.
The vulcanization was carried out in a hot press (QLB-400×400) for the optimum cure time determined by a disc rheometer. The test specimens were punched from the molded sheet along the fiber orientation. The specimen in which short fibers paralleled to the calender direction denotes as the longitudinal orientation direction (L direction), reversely as the transverse orientation direction (T direction).
Fourier Transform Infrared spectroscopic analysis (FTIR) was carried out using the Nicolet 380 spectrophotometer (Thermos Scientific, Inc.). All samples were scanned as total reflection from 600 cm−1 to 4000cm−1.
The cure characteristics including minimum torque (
Mechanical properties of the vulcanized composites were measured by using a universal tensile testing machine (Shenzhen sans Materials Testing Co., Ltd., China) under ambient conditions (at 25 ± 2°C). Tensile strength and tear strength were tested according to ASTM: D412-06-2 and ASTM: D624-00 (2012) standard, respectively. The speed of jaw separation was 500 mm/min. The hardness of the rubber composites was measured by Shore A hardness tester as per ASTM: D2240-05(2010) standard.
Wear resistance, representing in terms of volume loss, was performed using Akron-type abrasion tester WML-76.
Dynamic Mechanical properties were investigated using Netzsch DMA tester 242; the temperature sweep test was performed; i.e., the temperature was scanned from -20°C to 80°C at 5°C/min under frequency and tensile strain of 1Hz and 1%, respectively.
The morphology of fibers and the tensile fractured surface of composites were measured by using Scanning Electron Microscopy (XL-30FEG, Philips, Inc.) at an accelerating voltage of 10kV. The surface was sputter coated with a thin layer of gold before SEM observation.
The FTIR spectra of GPPE and fibers before and after modification are shown in Figure
FT-IR spectra of GPPE and short fibers with and without modification.
Furthermore it can be seen from Figure
Chahira Makhlouf [
Grafting mechanism.
The modified fiber (MNSF-2) was incorporated into SBR tread compounds formula. The effects of fiber contents and orientation on properties of tread compounds were investigated.
The cure characteristics of tread compounds with 2phr fibers and without fibers are shown in Figure
Effects of short fibers on cure characteristics of tread compounds.
Figures
Effects of MNSF-2 content on cure characteristics of tread compounds.
Effects of MNSF-2 content on t10 and t90 of tread compounds.
The superior interface adhesion of the modified fiber compounds to the unmodified fiber (NSF) has been verified by mechanical properties measurements as shown in Figure
Effects of fibers content and the orientation on mechanical properties of compounds.
The modified fibers showed reinforcing effect on rubber compounds. With the increase of MNSF-2, the tensile strength increased to a maximum value and then decreased slightly. Both modulus and tear strength of fiber compounds were significantly higher than that without fibers. The highest tear strength value was observed in 8phr MNSF-2 reinforced SBR compounds, with 31.9% increase compared to the gum rubber. Meanwhile, elongation at break value of MNSF-2/SBR compounds was higher than that of NSF/SBR compounds. It is known that the rigid short fibers are apt to restrict rubber matrix from deformation which contribute to elevated modulus and tear strength of composites [
MNSF-2 contents on stress-strain curves.
The introduction of C15 carbon chain group enhanced the hydrophobicity of MNSF-2, promoting the uniform dispersion of this fiber within rubber matrix. Meanwhile, the cocrosslinking reaction might occur between the MNSF-2 fiber and SBR during vulcanization process, resulting in improved interface bonding and comparative mechanical properties of the modified fibers/SBR tread compounds. Furthermore, the superior elongation at break of MNSF-2/SBR compounds confirmed the formation of flexible interfacial bond between fibers and rubber matrix [
In terms of the anisotropy characteristic, fibers aligned in L direction showed higher mechanical properties than in T direction, which should be due to the high L/D ratio and orientation of short fibers.
The effect of short fibers content on the wear volume of tread compounds is shown in Figure
Short fiber contents on wear volume of tread compounds.
The effects of modified fiber content on dynamic mechanical properties of the tread compound at various temperatures between -20°C and 80°C are shown in Figure
MNSF-2 content on E′ and
The relationship between MNSF-2 content and
The relationship between MNSF-2 content and
The SEM micrographs of short fibers and fractured surface of compounds are shown in Figure
SEM of short fibers and tread compounds.
NSF
MNSF-2
NSF tread compound
MNSF-2 tread compound
In this work short nylon fibers waste modified with GPPE was obtained by a simple two-step procedure. The effects of short fibers on vulcanization characteristics, mechanical properties, dynamic mechanical properties, and wear resistance of SBR tread compounds were investigated.
The fiber modified method and fibers contents affected the curing properties of rubber compounds. The addition of the MNSF-2 resulted in slightly lower
The deterioration of tensile strength and elongation at break of tread compound containing NSF was apparent. Conversely, the modified fibers showed reinforcing effect on tread compounds. The tensile strength values of compounds increased with MNSF-2 content, passed through a maximum value, and then reduced slightly. The modulus and the tear strength of compounds increased significantly with fiber loadings. The highest tear strength value was observed in 8phr MNSF-2 reinforced SBR compounds, with 31.9% higher than that of the gum compound, while elongation at break of the MNSF-2 compound maintains a relative high value than the NSF/SBR compounds.
The addition of NSF exaggerated abrasive volume of compounds at high fiber content. However, the wear resistance of MNSF-2 compounds is superior to that of NSF compounds and comparable with that of gum compound. The DMA results reveal that E′ and
The data used to support the findings of this study are available from the corresponding author upon request. There are no linked research data sets for this submission. The following reason is given: data will be made available upon request.
The authors declare that they have no conflicts of interest.
We would like to acknowledge the Science & Technology Key Program of Guangzhou, China (Grant No. 2013Y2-00116), South China Tire & Rubber Co., Ltd., for supporting this research.