Resins vinyl ester

Radical copolymerization of the cycloahphatic vinyl ester resin with methyl methacrylate monomer led to a crosslinked polymer characterized by high UV resistance. 

Styrene solutions of cycloahphatic epoxy-based divinyl ester resin (45, 50 and 55 wt % styrene) were prepared and modified with TDI at room temperature [67] (Table 19). 

Modification with TDI led to an increased viscosity of the resins, shorter gelation time in comparison with the parent resin, and to reduced exotherm peak temperature. The modified resins as well as the resins with a higher styrene concentration were more stable at elevated temperatures. An increase in TDI concentration also caused a significantly higher Tg and thermal resistance (by about 40 °C Table 20). However, the addition of TDI did not affect the hardness. The decrease in flexural strength of the prepared resins was 

Resin No Styrene concn. [%] TDI concn. [%] Density [g/cm ] Viscosity [mPas] Acid value [mgKOH/g] Gelation time [min] Peak exotherm temp. [°C] Stability at 60 °C [days] 

Resin No. Thermal resistance (Martens) [°C] Glass transition temperature Tg [°C] Impact strength (Charpy) [kl/m2] Ball TensUe indentation strength hardness [MPa] [MPa] Flexural strength [MPa] 

Typical properties of cast vinyl ester resins are listed in Table 4.5. 

The vinyl esters can, like polyesters, be divided into three groups on the basis of either elongation to break or load capability at high temperature. 

For these resins, a high heat distortion temperature goes with low elongation and vice versa. 

These resins are generally regarded as having properties between those of polyesters (Table 4.1) and epoxies (Table 4.9). This applies both to mechanical and chemical properties as well as the ease of use with various manufacturing processes. 

However, the cost of vinyl esters lies between those of polyesters and epoxies so advantages in properties have to be traded off against cost. 

A special class of unsaturated polyesters, developed for composite applications in corrosive environments, is the so-called vinyl esters and vinyl ester urethane resins. 

In Table 16.4, the UP, vinyl ester, and vinyl ester urethane resins are classified in order of chemical resistance. 

Reaction times vary from 8 to 30 h, depending on the raw materials used, the degree of condensation or molecular weight desired, and the reaction temperature employed. 

After cooling, the unsaturated polyester is discharged from the reactor into the so-called thinning tank, which has a preweighed styrene charge in it. The resin is then finished with additives, tested for quality control, and pumped to storage. 

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Vinylene shift Vinyl ester Vinyl ester resins... 

Vinyl ester resins generally offer mechanical properties superior to those of polyester matrices but at an increased cost. Vinyl esters are chemically similar to epoxy resins but are manufactured via a cold-curing process similar to that used in the manufacture of polyester resins. Vinyl esters offer superior resistance to water and chemical attack and are used in such appHcations as underground pipes, tank liners, and storage tanks (see Vinyl polymers). 

High-temperature cement formulations are basically polymer concrete. Mainly unsaturated polyesters or vinyl ester resins with allylphthalate as vinyl monomer are in use [927]. Cming is achieved with peroxides, which decompose sufficiently fast at temperamres between 120° and 200° C. Polymer concrete requires additional materials, which compensate shrinkage. 

Epoxy system curing profile, 10 17-18 Epoxy systems, post-cure for, 10 423 Epoxy vinyl ester composites, 10 452 Epoxy vinyl ester resins, 10 349 Epoxy vinyl esters, 10 383 Eprosartan, 5 187... 

The blending of DCPD resins has become an important practice. Typical blended resins include combinations of DCPD resins with isophthalic, orthoph-thalic or vinyl ester resins. Creating blends with higher-molecular-weight phthalic anhydride, isophthalic or vinyl ester resins can toughen neat DCPD resins, which are inherently brittle. In the case of vinyl ester and isophthalic and DCPD blends, a degree of improved chemical resistance and hydrolytic stability can be gained. 

In most applications, polyester and vinyl ester resins are used as the matrix materials. Epoxies are also used, although they require longer cure times and do not release easily from the pultrusion dies. Hence, thermosetting resins are most commonly used with pultrusion, although some high-performance thermoplastics such as PEEK and polysulfone can also be accommodated. In addition to the resin, the resin bath may contain a curing agent (initiator, cf. Section 3.3.1.2), colorants, ultraviolet stabilizer, and fire retardant. 

Because of all these minor components (e.g., catalysts and inhibitors, added to major ones) the cure of vinyl ester resins is very complex, involving many competitive reactions. There are some new variables to account for, such as the inhibitor and initiator concentrations and induction time. Several papers [81,96,200,201] use the mechanistic approach, claiming that the phenomenological models do not explicitly include these facts, resulting in a new parameter characterization after each change in resin formulation [96]. Despite these arguments, the phenomenological approach is the most widely used and is based on an autocatalytic model which has been successfully applied to epoxy resins. Many authors [30,34,74,199,202,203] proposed the Equation 2.30 to describe the cure kinetic of unsaturated polyesters ... 

Sheet molding compound (SMC) is a composite material that has been used as an alternative to steel for more than 30 years. SMC consists of a glass-fiber-filled unsaturated polyester and vinyl ester resin that has been compacted into a sheet. These sheets are then placed into compression molds and formed into body panels, and these panels are then coated mainly by dual-cure coatings. ... 

Hojo, H., Tsuda, K. Effects of Chemical Environments and Stress on Corrosion Behaviors of Glass Fiber Reinforced Plastics and Vinyl Ester Resin, Proc., 34th Ann. Tech. Conf., Reinf. Plast./Compos. Inst., SPI, Sec. 13-B, 1979... 

In the same way, ABS acts as a toughener for vinyl ester resins (34). Assessment of the mechanical properties suggest that a chemical reaction may have occurred between the constituents of the blends. The blends are intended as a toughening agent for interlayer toughened vinyl ester/glass composite materials. 

VINYL ESTER RESINS. The vinyl ester resins are a relatively recent addition1 to thermosetting-polymer-chemistry. Superficially, they are similar to unsaturated polyester resins insofar as they contain ethylmic lmsaturation and are cured throngh a free-radical mechanism, usually in the presence of a vinyl monomer, such as styrene. However, close examination of the chemistry and structure of the vinyl ester resins demonstrates several basic differences which lead to their unique characteristics. 

Vinyl ester resins arc manufactured through an addition reaction of an epoxy resin with an acrylic monomer, such as acrylic acid, methaciylic add. or the half-ester product of an hydroxyalkyl acrylate and anhydride. In contrast, the polyester resins are condensation products of dibasic acids and palyhydric alcohols. The relatively low-molecular-weight precise polymer structure of the vinyl ester resins is in contrast to the high-molecular-weight random structure of the polyesters. 

Of particular importance in describing the difference between these two families of resins are the locations of die reactive unsaturation. In the polyester resin, these groups are located along the backbone of die polymer with terminal hydroxyl or carboxylic acid groups. The vinyl ester resins contain no significant acidity but terminate in reactive vinyl ester groups. Because of the location of these reactive sites, the vinyl ester resins will homopolymerize as well as coreact with various vinyl monomers. 

The free-radical cure mechanism of the vinyl ester resins is well understood. In most respects, it is similar to that of the unsaturated polyester resins. To initiate the curing process, it is necessary to generate free radicals within Ike resm mass. Organic peroxides are tlie most common source of free radicals. These peroxides will decompose under the influence of elevated temperatures or chemical promoters, e.g., organometallics or tertiary amines, to form free radicals. Generation of free radicals also can be effected by ultraviolet or high-energy radiation applied directly to the resin system. The free radicals thus formed react to open the double bond... 

TABLE 1. PROPERTIES OF TYPICAL UNCURED VINYL ESTER RESINS... 

P. H. Cook, Dow Chemical USA., and operating unit of the Dow Chemical Company. Freeport, TX. Vinyl Ester Resins David A. Cooney, National Cancer Institute, Bclhesdu, MD. hltp //wvvw. nci.nih.gov/. Enzyme Therapeutic... 

Core-shell rubber (CSR) particles are prepared by emulsion polymerization, and typically exhibit two or more alternating rubbery and glassy spherical layers (Lovell 1996 Chapter 8). These core-shell particles are widely used in thermoplastics, especially in acrylic materials (Lovell, 1996), and have also been used to modify thermosets, such as epoxies, cyanates, vinyl ester resins, etc. (Becu et al., 1995). 

Thermoset resins covers an extremely wide range, including phenol formaldehyde polymers, aminopolymers, PUs, epoxies, and thermoset polyesters, which include the alkyd and unsaturated vinyl ester resins. Of special interest at the present time are those that comprise the resin component of liber-reinforced composites that are finding increasing use in commercial and defense sectors, where fire resistance is of paramount importance. Typical resins used are those listed in Table 2.4 along with typical, respective LOI values in descending order of increased inherent fire resistance. 

Chigwada et al.36 have combined polyhedral oligosilsesquioxanes (POSS), which are cage-like hybrid molecules of silicon and oxygen, with TCP (tricresylphosphate) in poly(vinyl ester) resins (PVE). POSS molecule contains nonreactive organic functionalities allowing solubility and compatibility of the POSS with various polymers. POSS was incorporated alone (3-10 wt %) in PVE, and four compositions were made with TCP at 4wt % POSS + 4wt % TCP and 5wt % POSS + 5, 10, 15 wt % TCP. Fligh reductions in PHRR and THR were noticed. Nevertheless, the POSS/ TCP combination did not exhibit better performances than compositions with only 5 or 10 wt % of TCP alone. 

FRP materials are made up of the polymer and reinforcing fibers. The polymer is typically a thermoset polymer thermoplastics can be used as well. Some typical thermoset polymers used are epoxy resins, unsaturated polyester resins, epoxy vinyl ester resins, phenolic resins, and high performance aerospace resins such as cyanate esters, polyimides, and bismaleimides. These resins... 

For commodity applications, there are four major classes of resins that are used in FRP applications. They are phenolic resin, epoxy resin, unsaturated polyester resin, and epoxy vinyl ester resins. A more complete description of these types of resins and their many variations can be found in Handbook of Thermoset Plastics. This is not a comprehensive list of resins used in composite manufacture, as commodity materials like polyurethanes and isocyanurate resins are sometimes used as well to make FRP parts. However, these materials are not covered in this chapter owing to their limited use, but, the principals of fire safety that apply for the resins described subsequently apply to these materials as well. 

Epoxy vinyl ester resins are a special class of unsaturated resin. This resin is made by capping an epoxy resin with methacrylic acid and then dissolving in styrene monomer to the desired viscosity. This gives mechanical properties similar to epoxy resins, but the processibility (low viscosity allowing for resin infusion processes) of an unsaturated polyester resin. As with unsaturated vinyl esters, the most common fire retardant vinyl ester resin is based on a resin made from a halogenated system, tetrabromobisphenol A. The level of bromine in the resin and the presence of antimony will determine the fire performance of the resin. These resins are normally used for corrosion resistant equipment or when fire performance and high mechanical properties are required. It is very difficult to get a low smoke value with a brominated vinyl ester resin again due to the fact that bromine... 

Two resins were used to do the first study on laminate construction. The first was a brominated epoxy vinyl ester resin with antimony pentoxide and the second was a brominated unsaturated polyester resin. They were both promoted to cure at room temperature with methyl ethyl ketone peroxide catalyst. The panels were then postcured at 250°F (121°C) for 8 h. Panels were prepared that varied in glass content from 25% to 70% and panel thickness varying from 0.05 in. to 0.25 in. and were tested at the same testing facility. A summary of the FSI test data for the first set of panels tested are shown in Figures 23.1 and 23.2. This graph in Figure 23.1 plots the FSI value versus the panel thickness. This data would indicate that the thickness of the test panel has no effect on the measured... 

Gilman, J.W., Kashiwagi, T., Nyden, M., Brown, J.E.T., Jackson, C.L., Lomakin, S., Giannelis, E.P., and Manias, E., Flammability studies of polymer layered silicate nanocomposites Polyolefin, epoxy, and vinyl ester resins, in Chemistry cmd Technology of Polymer Additives, Al-Malaika, S., Golovoy, A., and Wilkie, C.A., (Eds.), Blackwell Science, Oxford, U.K., 1999, Chapter 14, pp. 249-265. 

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