Study On Preparation Of A Nylon-like Polyester Tire Cord And Its Properties Of Rubber Composite

Textile fiber-reinforced mechanical rubber composites have been applied in many areas,such as transmission belt,conveyor belt,pneumatic tire and hose.Among them tire is probably the most common type,which is more complicated than what it appears to be and could be regarded as an organic object with a structural skeleton of tire cords fleshed with rubber compound.In which fiber cords are embedded in the rubber matrix,carrying a large scale of structural load and maintaining a stable contour of the tire,while on the other hand,rubber compound is providing cushioning effect to surface irregularities and transferring load to cords.Due to the limit of properties or price,single type of fiber cords is less likely to meet hierarchical purposes,thus hybrid or composite cords are then developed to optimize the properties.In this thesis,a nylon-like polyester was prepared by optimizing the molecular structure and morphology design of high modulus low shrinkage(HMLS)polyester fiber.Its stress-strain curve showed a high modulus typical for standard polyester cord in small deformation,while a high elongation as nylon cord at ultimate deformation,creating a hybrid effect.The main reseach contents and conclusions are depicted in the following:In the high-speed spinning of HMLS polyester fiber,physical properties of fibers at different forming stages were determined by evolution of their super-molecular structures.WAXD,SAXS,DMA,DSC and Instron were adopted to analyze the relationship between properties and super-molecular structure along the fiber spinning line.Results showed that the molecular chains of fiber were getting ordered and crystalized under the complex coupling effect of temperature and stress filed along the spinning line.Undrawn fiber was forming primary crystal structure at the first stage;structure and crystallinity were becoming perfect and growing with further stretching.Meanwhile crystal grains and crosslink of molecular chains formed a rubber-like net structure,which prohibited the mobility of molecular chains,thus leading to high modulus and low shrinkage.During the final thermal setting process,orientation factor of amorphous chains decreased slightly due to the rubber-like net structure,resulting in breaking strength decreased,breaking elongation increased accordingly,thermal dimensional stability improved as well.A new type of HMLS polyester fiber was then designed based on the early studied theory.Morphology and dual dipping process parameters of this new HMLS polyester fiber were optimized with the help of design of experiment(DOE),thus a nylon-like polyester tire cord was prepared.Twist level can improve the cohesion of fiber bundle,which had an evident effect on breaking strength,breaking elongation,fatigue property and rubber adhesion performance.Due to the lack of enough polar agents,a dual dipping system was applied to improve rubber adhesion.Molecular chains of nylon-like polyester were rearranged during the dipping process.Crystal structure was intended to be more stable under the complex effect of temperature and stress filed;low orientation factor of amorphous was the main reason to enable nylon-like polyester having this hybrid effect.Static physical properties and static adhesion to rubber compound of nylon-like polyester tire cord were evaluated.Results showed that EASL@ 66.6N(modulus)and dimensional stability index(DSI)of nylon-like polyester tire cord were laid between standard polyester and nylon cords.Breaking elongation of nylon-like polyester was around 21.7%,which was much higher than standard polyester tire cord(16.2%),and close to nylon cords(approximately 23.5%).High modulus and DSI would contribute to the handling performance;high breaking elongation would improve impact resistance property.Nylon-like polyester cord exhibited the same level of static adhesion to standard polyester cord,but lower than nylon cord,which was determined by the nature of materials.In real working condition,tire cords are subjected to periodical mechanical loading,dynamic experiments could be better to evaluate characteristics of tire cords.Results showed that dynamic modulus and dynamic DSI under different temperature were between standard polyester and nylon cords,which was in accordance to its static properties.DISC experiments revealed that prior to compression ratio of 25%,all three kind of tire cords were roughly at the same level,while beyond this ratio,fatigue resistance property of standard polyester dropped sharply,nylon-like polyester behaved similarly to nylon 6.Flex fatigue experiment showed that when surface temperature of specimen was prior to 85?,nylon-like polyester had similar dynamic adhesion property,but beyond this temperature,dynamic adhesion property of nylon-like polyester was deteriorated quickly.Nylon-like polyester tire cord presented practicable dimensional stability,comparable adhesion and a favorable fatigue resistance,combining positive characteristics of both standard polyester and nylon cords.Finally,both motorcycle and all-terrain vehicle(ATV)tires were deployed to validate the characteristics of nylon-like polyester tire cord.Result showed that high modulus and high dimensional stability of nylon-like polyester enabled tires to have a better handling performance compared to nylon control tires.Rolling resistance experiment revealed that nylon-like polyester motorcycle tire had a lower rolling resistance,which can help improve fuel efficiency.