Modification of Unsaturated Polyester Resin by Polyurethane Prepolymers

Unsaturated polyester resins (UPRs) are extensively used by the fiber-reinforced plastic (FRPs) industry. These resins have the disadvantages of brittleness and poor resistance to crack propagation. In this study, UPRs were chemically modified by reactive blending with polyurethane prepolymers having terminal isocyanate groups. Hybrid networks were formed by copolymerisation of unsaturated polyesters with styrene and simultaneous reaction between terminal hydroxyl groups of unsaturated polyester and isocyanate groups of polyurethane prepolymer. The prepolymers were based on toluene diisocyanate (TDI) and each of hydroxy-terminated natural rubber (HTNR), hydroxy- terminated polybutadiene (HTPB), polyethylene glycol (PEG), and castor oil. Properties like tensile strength, toughness, impact resistance, and elongation-at-break of the modified UPRs show considerable improvement by this modification. The thermal stability of the copolymer is also marginally better

Effect of processing parameters on the mechanical properties of short Kevlar aramid fibre-thermoplastic polyurethane composite

The effect of various processing parameters, such as nip gap, friction ratio and roll temperature, on the tensile properties of short Kevlar aramid fibre-thermoplastic polyurethane composite has been investigated and the tensile and tear fracture surfaces have been characterised using a scanning electron microscope. A nip gap of 0.45 mm, a friction ratio of 1.15 and a roll temperature of 62°C was found to give optimum mechanical properties. Scanning electron microscopy study revealed a higher extent of fibre orientation in the milling direction in the above condition.

Scanning Electron Microscopy Studies on Tear and Wear Failure of Short Kevlar Fiber-Thermoplastic- Polyurethane Composite

Tear and wear properties of short kevlar fiber, thermoplastic polcurethane (TPU) composite with respect to fiber loading-and fiber onentation has been studied and the fracture surfaces were examined under scanning electron microscope (SEM). Tear strength first decreased up to 20 phr fiber loading and then gradually increased with increasing fiber loading. Anisotropy in tear strength was evident beyond a fiber loading of 20 phr. Tear fracture surface of unfilled TPU showed sinusoidal folding characteristics of high strength matrix. At low fiber loading the tear failure was mainly due to fibermatrix failure whereas at higher fiber loading the failure occurred by fiber breakage. Abrasion loss shows a continuous rise with increasing fiber loading, the loss in the transverse orientation of fibers being higher than that in the longitudinal orientation. The abraded surface showed lone cracks and ridges parallel to the direction of abrasion indicating an abrasive wear mechanism. In the presence of fber the abrasion loss was mainly due to fiber low.

Self adhesion of short Kevlar fibre -thermoplastic polyurethane composite

The self adhesion behaviour of thermoplastic polyurethane (TPU) in itself and its composite with short Kevlar fibre with respect to contact time, temperature, pressure, and fibre loading has been studied. The adhesion strength showed two linear increments of different slopes with respect to the square root of time: with temperature and pressure of contact, the adhesion strength was improved. The maximum strength was obtained with 20 phr of short fibre in only one of the mating substrates in the peel test sample. The duration for wetting and diffusion was shifted to longer time intervals with fibres loaded in both the substrates.

Studies on the Effect of an External Flaw on the Tensile Strength of Short Kevlar Fiber-Thermoplastic Polyurethane Composites

The effect of an external flaw on the tensile strength of short kevlar fiber-thermoplastic composites has been studied with respect to fiber content, fiber orientation, location of the external flaw, and the temperature of test. The composites showed a three-step reduction in tensile strength with increasing flaw size. The critical flaw-length region was shifted to higher flaw-size levels with increasing fiber content. With increasing temperature, the critical flaw length was increased in the case of unfilled TPU, whereas it remained more or less constant in the case of short kevlar fiber-filled-TPU composite.

Studies on the Flammability of Short Kevlar Fiber-Thermoplastic Polyurethane Composite

The flammability of short Kevlar aramide fiber-thermoplastic polyurethane (TPU) has been investigated with respect to fiber loading and various flame retardant additives such as halogen containing polymers, antimony oxide/chlorine donor combination, zinc borate, and aluminum hydroxide. Smoke generation was reduced drastically, while the oxygen index was reduced marginally in the presence of short fibers. The best improvement in the oxygen index was obtained with antimony oxide/chlorinated paraffin wax combination, in the weight ratio 1:6. A 70 phr loading of aluminum hydroxide improved LOI and reduced smoke generation.

Rheological Properties of Short Polyester Fiber-Polyurethane Elastomer Composite with Different Interfacial Bonding Agents

The rheological behavior of a short-polyester-fiber-filled polyurethane elastomer composite containing different bonding agents has been studied in the temperature range 120-160°C and in the shear rate range 63-608 s-'. The composite with and without bonding agents showed a pseudoplastic behavior which decreased with the increase of temperature. Composites containing bonding agents based on polypropyleneglycol and 4,4'-diphenylmethanediisocyanate showed the lowest viscosity values at a particular shear rate, whereas composites containing a glycerol- (GL) based bonding agent showed the highest viscosity. The viscosity of the composite decreased sharply after a particular temperature (140°C) and the fall was less drastic in the composite containing a GL-based bonding agent.

Stress Relaxation of Polyester Fiber-Polyurethane Elastomer Composite with Different Interfacial Bonding Agents

The stress relaxation behavior of polyurethane elastomer and short polyester fiber filled elastomer composites with and without bonding agents at different strain levels and strain rates was studied. It was found that these compounds exhibit a multistage relaxation mechanism and that the rate of relaxation and cross-over time depend on the strain level and strain rate. The incorporation of fibers reduced the stage-I relaxation rate and increased the cross-over time of the gum vulcanisate. A higher rate of relaxation (first stage) was shown by the composites with longitudinal fiber orientation and composites with bonding agents.

Studies on the curing of short polyester fiber-polyurethane elastomer composite with different interfacial bonding agents

The cure characteristics of short fiber-polyurethane elastomer were studied with respect to different fiber-matrix bonding agents. A hexamethylenetetramine- resorcinol -hydrated silica based bonding agent was found to affect the stability of the composite. A new bonding agent, TP resin, based on polymeric toluenediisocyanate and polypropylene glycol has been developed. Cure characteristics of the composite with and without TP resin at different fiber loadings were also compared. Minimum torque, scorch time and optimum cure time increased with fiber content. Maximum torque was consistently higher with TP resin at all fiber loadings.

Thermal degradation of short polyester fiber polyurethane elastomer composite

The thermal degradation of short polyester fiber reinforced polyurethane composites with and without different bonding agents has been studied by thermogravimetric analysis . It was found that degradation of the polyurethane takes place in two steps and that of the composites takes place in three steps. With the incorporation of 30 phr of fiber in the matrix , the onset of degradation was shifted from 230 to 238 ° C. The presence of bonding agents in the virgin elastomer and the composite gave an improved thermal stability . Results of kinetic studies showed that the degradation of polyurethane and the reinforced composites with and without bonding agents follows first -order reaction kinetics

Thermal degradation of short kevlar fibre thermoplastic polyurethane composite

The thermal degradation of short kevlar fibre-thermoplastic polyurethane (TPU) composites has been studied by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). TGA showed that the thermal degradation of TPU takes place in two steps with peak maxima (T1max and T2ma,) at 383°C and 448°C, respectively. In the presence of 10-40 phr of short kevlar fibres, T1_ and T2max were shifted to lower temperatures. The temperature of onset of degradation was increased from 245 to 255°C at 40 parts per hundred rubber (phr) fibre loading. Kinetic studies showed that the degradation of TPU and kevlar-TPU composite follows first-order reaction kinetics. The DSC study showed that there is an improvement in thermal stability of TPU in the presence of 20 phr of short kevlar fibres.

Studies on polyurethane elastomers based on liquid natural rubber

In the present study, the photochemical depolymerisation of NR in toluene, in presence of H202 and a homogenizing solvent (Methanol/Tetrahydro— furan) so as to get hydroxyl terminated liquid natural rubber (HTNR) has been carried out. The copolymeri— sation of this product with butane 1,4 diol and toluene 2,4 diisocyanate in presence of a catalyst, dibutyl tin dilaurate, to produce polyurethanes with HTNR soft segments is also reported. The preparation of block copolymers based on poly(ethylene oxide) with varying molecular weights and HTNR are also discussed along with a detailed study on their thermal and mechanical properties

“Studies on short polyester fiber - polyurethane elastomer composite with different interfacial bonding agents”

The work presented in this thesis is regarding the development and evaluation of new bonding agents for short polyester fiber - polyurethane elastomer composites. The conventional bonding system based on hexamethylenetetramine, resorcinol and hydrated silica was not effective as a bonding agent for the composite, as the water eliminated during the formation of the RF resin hydrolysed the urethane linkages. Four bonding agents based on MDI/'I‘DI and polypropyleneglycol, propyleneglycol and glycerol were prepared and the composite recipe was optimised with respect to the cure characteristics and mechanical properties. The flow properties, stress relaxation pattern and the thermal degradation characteristics of the composites containing different bonding agents were then studied in detail to evaluate the new bonding systems. The optimum loading of resin was 5 phr and the ratio of the -01 to isocyanate was 1:1. The cure characteristics showed that the optimum combination of cure rate and processability was given by the composite with the resin based on polypropyleneglycol/ glycerol/ 4,4’diphenylmethanediisocynate (PPG/GL/MDI). From the rheological studies of the composites with and without bonding agents it was observed that all the composites showed pseudoplastic nature and the activation energy of flow of the composite was not altered by the presence of bonding agents. Mechanical properties such as tensile strength, modulus, tear resistance and abrasion resistance were improved in the presence of bonding agents and the effect was more pronounced in the case of abrasion resistance. The composites based on MDI/GL showed better initial properties while composites with resins based on MDI/PPG showed better aging resistance. Stress relaxation showed a multistage relaxation behaviour for the composite. Within the-strain levels studied, the initial rate of relaxation was higher and the cross over time was lesser for the composite containing bonding agents. The bonding agent based on MDI/PPG/GL was found to be a better choice for improving stress relaxation characteristics with better interfacial bonding. Thennogravimetirc analysis showed that the presence of fiber and bonding agents improved the thennal stability of the polyurethane elastomer marginally and it was maximum in the case of MDI / GL based bonding agents. The kinetics of degradation was not altered by the presence of bonding agents

Cure Characteristics of Short Polyester Fiber-PolyurethaneElastomer Composite with Interfacial Bonding Agents Based on Polymeric 4,4'-Diphenylmethanediisocyanate

Cure characteristics of short polyester fiber-polyurethane composites with respect to different bonding agents (MD resins) based on 4, 4' diphenylmethanediisocyanate (MDI) and various diols like propyleneglycol (PG), polypropyleneglycol (PPG) and glycerol (GL) were studied. Tmax. - Tmin. of composites having MD resin were found to be higher than the composite without MD resin. Minimum torque and Tmax. - Tmin., scorch time and optimum cure time were increased with the increase of MDI equivalence. Optimum ratio of MDI / -of in the resin was found to be within the range of 1-1.5. It was observed from the cure characteristics that for getting better adhesion between short polyester fiber and the polyurethane matrix the best choice of MD resin was one based on MDI and 1:1 equivalent mixture of polypropyleneglycol and glycerol.