Polyester resins flexural strength

Carbon-Fiber Composites. Cured laminates of phenoHc resins and carbon-fiber reinforcement provide superior flammabiHty resistance and thermal resistance compared to unsaturated polyester and epoxy. Table 15 shows the dependence of flexural strength and modulus on phenoHc—carbon-fiber composites at 30—40% phenoHc resin (91). These composites also exhibit long-term elevated temperature stabiHty up to 230°C. 

Figures 10 and 11 show the weight change and the retention of strength for iso-phthalic unsaturated polyester resin (iso-UP). These behaviors show almost the same tendency as MTHPA-EP, however, as shown in Figure 12 the concentration influences flexural strength and the strength becomes minimum at the concentration of 30wt%. This behavior is thought to depend on contradictory tendency of the wetability and the reactivity with the concentration.

Figure 7. The pH of aqueous silane treament (1%) on SiO vs. flexural strength of polyester castings (50% 5 fim minusil in resin).

The procedure to obtain nanocomposites based on unsaturated polyester resins leads to improvements in the order of 120% in the flexural modulus, 14% in flexural strength and 57% increase in tensile modulus with 4.7% of clay slurry content. Thermal stability augments and the gelation temperature increases to 45 °C, as compared to that of the resin (Fig. 31.6). It seems that adding water to the MMT allows better intercalation of polymer chains into the interlamellar space. Because clay is first suspended in water, this improves dispersion and distribution of the particles in the resin matrix. Longer gelation times lead to more uniform and mechanically stronger structures and to yield stresses (Fig. 31.7). Enhanced polymer-clay interactions are revealed by XPS in this case (Fig. 31.8). 

In 1971, one of the first pipes was installed in the UK in London in the form of 1.17 X 0.61 m egg shaped profiles. A polyester felt mat tube impregnated with an isophthalic polyester resin was installed and cured in place. After 20 years, a section of the pipe was taken out of service and the strength properties were measured. The cured-in-place pipe retained its properties and still had a flexural strength that was 30% over the initial installation requirements. The parts showed no sign of wear or deformation. Several other pipe sections have been checked after years of service and found to be virtually unchanged. 

The work emphasized shredded carpet selvage to which various amounts of cut waste fibers such as nylon 6, nylon 6,6, polyester, and cotton were added. Fabric bits of waste denims and cotton-polyester fabrics were also used. The waste carpet blend was then coated with phenolic or urea formaldehyde resins that were dispersed in a water base. The composites contained various amounts of different fibers or fabrics and 7.5-20 wt% adhesive solids with respect to the fiber content. The fibers were spray coated and molded in a heated press at 150-200°C and 3.4 MPa. Test results show that one can achieve high flexural moduli of 2.4-2.S GPa with face yam, that is, fibers that bind to the matrix snch as nylon, polyester, and cotton. These values together with flexural strengths of 34-48 MPa make the products suitable for many outdoor and transportation applications. 

Table 4.40 Influence of temperature on short term flexural strength retention of FRP laminates, fabricated from several types of polyester resin (typical).

Figure 13. Flexural strength of the copolymers of the precipitates of y-MPS hydrolyzates and unsaturated polyester resin.

---