UP resin

Figure 18 Tensile strength of B.M.C. molded plastics as dependent on their fiber content. %fibers = g fibers/100 g UP resin.

Tests by Roe et al. [63] with unidirectional jute fiber-reinforced UP resins show a linear relationship (analogous to the linear mixing rule) between the volume content of fiber and Young s modulus and tensile strength of the composite over a range of fiber content of 0-60%. Similar results are attained for the work of fracture and for the interlaminate shear strength (Fig. 20). Chawla et al. [64] found similar results for the flexural properties of jute fiber-UP composites. 

Figure 20 Influence of fiber content by volume on tensile strength. Youngs modulus, work of fracture, and interlaminate shear strength of one-dimensional jute fiber-reinforced UP resins [63].

In manufacturing and processing in GRP plant, styrene and solvents must be extracted to prevent excessive concentrations in the air. In 1987 the permitted work-place concentration for styrene was reduced from lOOppm to 20ppm. From 31-12-94 values above 20ppm are no longer permitted where UP resins are processed manually. Exact measurement of concentrations is essential and suitable extraction systems installed. 

In MTHPA-EP and iso-UP resins, the strength of the resin below the corroded layer of specimen was same as that of before immersion. Assuming that the corroded layer has no strength, the prediction of strength after immersion was made by estimating the corrosion depth in the following way. 

Various methods ofachieving preconcentration have been applied, including Hquid -hquid extraction, precipitation, immobihzation and electrodeposition. Most of these have been adapted to a flow-injection format for which retention on an immobihzed reagent appears attractive. Sohd, sihca-based preconcentration media are easily handled [30-37], whereas resin-based materials tend to swell and may break up. Resins can be modified [38] by adsorption of a chelating agent to prevent this. Sohds are easily incorporated into flow-injection manifolds as small columns [33, 34, 36, 39, 40] 8-quinolinol immobilized on porous glass has often been used [33, 34, 36]. The flow-injection technique provides reproducible and easy sample handhng, and the manifolds are easily interfaced with flame atomic absorption spectrometers. 

Maleic anhydride [R1 equals -CH=CH- in Eq. (2.7) cis isomer] is reacted with aliphatic diols to form low molar mass unsaturated polyesters, UP. For molar masses higher than 1000 g/mol, products are diluted with a liquid vinyl monomer, most often styrene. This reactive mixture, generally called unsaturated polyester, UP resin, can be transformed into crosslinked polymers through a free-radical chain polymerization (see Sec. 2.3). 

Similarly to UP resins, VE resins consist of an unsaturated oligomer dissolved in styrene. The unsaturated oligomer is based on the epoxy chemistry (Sec. 2.2.4). When one mole of a DGEBA monomer is reacted with 2 moles of (meth)acrylic acid, an a, oo-di(meth)acrylate oligomer is obtained ... 

VE resins are more expensive than UP resins. They are used as matrices for glass-liber composites when a better corrosion resistance is needed. 

Triallyl cyanurate (TAC) and triallyl isocyanurate (TAIC) are used as crosslinking agents for methacrylates and UP resins to improve heat and solvent resistance as well as thermooxidative stability. 

Figure 8.3 Phase diagram for styrene (S)-unsaturated polyester (UP) prepo-lymer-PVAc ternary blends at T = 23°C,-D- UP Mn = 1690 g.moMand Mw/ Mn = 7.5 -o- UP Mn = 1480 g.mor1 and Mw/ Mn = 3.1. The dashed triangle represents the formulation range of typical industrial UP resins. (Reprinted from Suspene et al., 1991, Copyright 2001, with permission from Elsevier Science)...

In the case of modified UP resins, the situation is complicated by the fact that an inmiscibility region develops between the monomer and polymer also. Complex morphologies may result, such as the bicontinuous structures obtained for PVAc - UP resin blends when < )M0 > 7 wt%. 

The world wide consumption in 1997 of urea- and melamine-formaldehyde resins was 8xl06 nr phenolic resins 2.8 xlO6 m UP-resins 2.9 xlO6 t and EP-resins 1.5 x 106 t. 

Fig. 4. Shear rate-controlled relaxation experiment at f= 0.5 s (conditioning), 500 s (shear thitming), and 0,5 s" (relaxation) of 3% N20 and H18 dispersed in VE and UP resins.

For N20 dispersions in UP and VE resins a different behavior is observed. N20-VE resin dispersions containing 65% of resin show liquid behavior with low storage modulus and G < G". Addition of styrene increases the storage modulus with G > G". Hence, a viscoelastic solid is obtained. N20-UP resin dispersions with a resin content of 65% already show the properties of a viscoelastic solid ((7 > ( ). However, addition of styrene only slightly increases the storage modulus. 

SMC is a flat sheetlike compound, produced on a continuous moving belt process. The thermoset precursor is an UP-resin composed of an unsaturated polyester... 

The first derivatives of conductivity itself and of its logarithm are shown in Figure 13.2b, and it is obvious that the graph of the first derivative of In a is useless because the data are skewed and scattered. On the other hand, if the first derivative of untransformed conductivity is plotted the reaction periods become obvious. The first derivative of conductivity is zero while there is no change, and increases if the rate of reaction increases, as in the first part of the propagation period the unsaturated polyester (UP) resin crosslinking reaction of (in this example) when the rate is controlled by... 

FIGURE 13.3 (a) The Arrhenius plots of the rates of UP resin radiation-initiated crosslinking in the tem-... 

By using the point at which the first derivation of raw conductivity data became zero at the end of the reaction, vitrification time of radiation crosslinked UP resins was determined. Vitrification times in the range 293-345 K were approximately constant below upper liquid-liquid transition temperature but exhibited significant temperature dependence above the transition, which can be seen in the Arrhenius plot in Figure 13.3b. In the same manner, electrical field dependence of vitrification was also observed—the stronger the field, the earlier the system reached vitrification. 

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