The Research On Dipping Process And Performance Of HMLS PEP Cords

Due to excellent mechanical properties and dimensional stability, high-modulus andlow-shrinkage (HMLS) polyethylene terephthalate (PET) Cords were widely used as reinforcedcomposites for car tires, seat belts, industrial hose, and other fields. The interface bondproperties of composite material would directly affect the comprehensive performance. PETfiber was relatively a chemical inert polymer, and as a result, it merely possessed insufficientadhesion to rubbers. The traditional resorcinol formaldehyde latex (RFL) adhesive had still pooradhesion to PET fiber. So new surface treatment and bonding technology were required toimprove the adhesion between PET Cords and rubber.In this work, the effect of bonding-activated agent on the heat shrinkage, mechanicalproperties, crystallinity and thermal stability of HMLS and activated HMLS PET cords werestudied. Then the bonding formation and failure mechanism between PET fibers and rubberwere discussed through one-step process for dipping activated HMLS PET cords and two-stepprocess for dipping HMLS PET cords.Through the studies of bonding-activated agent, PET properties improved evidently,including lower shrinkage, higher breaking strength maintance and smaller breaking elongation.X-ray diffraction showed that crystallinity slightly increased after activation. The activatedreaction might take place from amorphous to prospective area. TG result displayed that thetemperature and remained quality of thermal decomposition increased, which meant theimprovement of thermal stability.The research of one-step process for dipping activated HMLS PET Cords in RFL andisocyanate-contained RFL adhesives showed that the best dipping time was both120s. H-pullforce significantly increased about12-18%due to the addition of reversibly blockedpolyisocyanate. FTIR-ATR analysis indicated that the bonding-activated agent was introducedinto the surface of PET, and doughty covalent crosslinking generated between vinyl pyridineand hydroxyl-group from phenolic. Scanning Electron Microscopic(SEM) showed that adhesivewas significantly adhered to PET surface after RFL and isocyanate-added RFL dipping. A standard H-pull test in which the cord pulled out was clean, that is, had little or no latex rubberadhering to it so that interface slipped. TG result stated clearly that thermal stability improvedobviously by RFL dipping.Two-step process for dipping HMLS PET cords demonstrates that the best dipping time is120seconds for pre-coated step and180seconds for the second step. On this basis, orthogonaltest drew that influence of technological parameters on the final adhesive performance wasshown in descending order as follows: deblocking temperature> heat setting temperature> heatsetting time> deblocking time> epoxy: water (mass ratio). Meanwhile, variance analysisshowed that the deblocking temperature, heat setting temperature and time have remarkableeffect on adhesive properties. Finally, the best process parameters were obtained: thedeblocking temperature was200℃, heat setting temperature was200℃, heat setting time was60s, deblocking time was90s and epoxy: water (mass ratio) was1:130. And then the result ofsingle factor experiment had the same changing tendency with the orthogonal experiment.FTIR-ATR analysis demonstrated that there were covalent cross linking occurredsimultaneously between the epoxy resin and the surface of PET cords as well as RFL adhesives.Double butadiene among RFL fillet was cross-linked with double bond of rubber in order toform good adhesion. SEM images sh3bowed that the surface of the pulled out cord wassubstantially completely coated with rubber, which was characteristic of cohesive failure. TGanalysis indicated that thermal stability improved after two-step dipping process.