Polyurethane Thermoset system

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

Polyurethanes Thermosetting polyurethane adhesives can be used for structural applications. They are normally two-component systems based on an isocyanate resin, the second component being one of a number of hardeners. Some thermoplastic solvent-based polyurethanes are available. 

Daron 40 Unsaturated polyester/polyurethane thermosetting blends for fiber-filled systems DSM... 

Material types such as thermosetting polyurethane resin systems are designed to have inherent flexibility, tear strength and impact resistance, which in many cases are required by the coatings. 

ASP Water-washed kaolin, Engelhard Aspun Fiber grade resins, Dow Astrawax Amide wax, additive lubricant, AlliedSignal Adac Thermoset polyester, Reichhold Attain ULDPE, Dow Aurum Polyimide resin, Mitsui Auto-Grader Online melt flow indexer, Brabender Autofiroth Pressurized rigid froth polyurethane foam systems, BASF Autoguage Automatic die. 

Premi-Gles Thermoset polyester-based molding compounds. Premix Prevail, Thermoplastic resins, Dow Prism Solid polyurethane RIM systems, Bayer... 

Thermoset systems including epoxide systems, polyesters, polyimides, and polyurethanes are cured more quicHy by microwave heating than by conventional thermal heating. This benefit of microwave heating was concluded from many studies reviewed by Zong et al. [19], with one typical example pertaining to the unimolecular imidization of a polyamic acid in N-methylpyrrohdone solution (see Scheme 1.5). 

Two chemical types generally used for pipeline repair arc epoxy and polyurethane (PU) resins. PUs have the advantage of curing at ambient temperatures via water activation, but the downside is that they are also easily hydrolysed in water and they have relatively low Tg values. In contrast, epoxy resins are more moisture stable and can be formulated to provide high Tg and environmental stability using aromatic amino compounds (Klein, 1991 Varma and Gupta, 2000). However, most thermosetting systems can only be applied on dry surfaces and are adversely affected by surface moisture and contaminants. Hence, ProAssure Wrap Extreme is a modified proprietary formulation that enhances adhesion in water environments. 

Thermoset polyurethane as a biader material for gravel systems is also under development. AppHcations could iaclude roofing systems that requite a high degree of uv light and abrasion resistance. 

The characteristics of the three most common thermoset resin systems used in pultrusion are compiled in Table 11.2 [3]. It is noteworthy that unreinforced polyesters and vinylesters shrink 7-9% upon crosslinking, whereas epoxies shrink much less and tend to adhere to the die. These epoxy characteristics translate into processing difficulties, reduced processing speed, and inferior component surface finish. It is normal practice to use resin additives to improve processability, mechanical properties, electrical properties, shrinkage, environmental resistance, temperature tolerance, fire tolerance, color, cost, and volatile evaporation. It is normally the resin, or rather its reactivity, that determines the pulling speed. Typical pulling speeds for polyesters tend to be on the order of 10-20 mm/s, whereas speeds may exceed lOOmm/s under certain circumstances. Apart from the resins characterized in Table 11.2, several other thermosets, such as phenolics, acrylics, and polyurethanes, have been tried, as have several thermoplastics (as will be discussed in Sec. 11.2.6). 

The parameter W2 is called the Arrhenius number. It varies from values of about 15 for low-activation energy systems (e.g., thermosetting polyurethanes), to values of about 40 for high-activation energy systems (e.g., phenolic molding compounds). 

Thermoset polyurethanes are cross-linked polymers, which are produced by casting or reaction injection molding (RIM). For cast elastomers, TDI in combination with 3,3,-dichloro-4,4,-diphen5lmethanediamine (MOCA) are often used. In the RIM technology, aromatic diamine chain extenders, such as diethyltoluenediamine (DETDA), are used to produce poly(urethane ureas) (47), and replacement of the polyether polyols with amine-terminated polyols produces polyureas (48). The aromatic diamines are soluble in the polyol and provide fast reaction rates. In 1985, internal mold release agents based on zinc stearate compatibilized with primary amines were introduced to the RIM process to minimize mold preparation and scrap from parts tom at demold. Some physical properties of RIM systems are listed in Table 7. 

A variety of polymers, both thermosets as well as thermoplastics, can be blended and coreacted with epoxy resins to provide for a specific set of desired properties. The most common of these are nitrile, phenolic, nylon, poly sulfide, and polyurethane resins. At high levels of additions these additives result in hybrid or alloyed systems with epoxy resins rather than just modifiers. They differ from reactive diluents in that they are higher-molecular weight-materials, are used at higher concentrations, and generally have less deleterious effect on the cured properties of the epoxy resin. 

Conventional industrial coatings materials of the thermoset type are usually acrylic, polyester, epoxy, polyurethane or silicone resins dispersed or dissolved in organic or water/ether-alcohol coupling solvents. They are cured with gas convection or electric IR ovens. The raw materials for the polymers come from petroleum feedstocks which are processed or manufactured into a finished coating system. 

There are RIM systems based on chemistry unrelated to polyurethanes that are not in significant commercial production compared to the polyurethanes. Development work has taken place with materials such as nylon. The nylon RIM material is based on caprolactam. Nylon RIM polymers offer high toughness and abrasion resistance. Polydicyclo-pentadiene is a proprietary thermoset polymer developed by Hercules. PCPD offers high-impact resistance and stiffness. It is used in the production of snowmobile components. Other polymers are used such as epoxies, polyesters, acrylics, phenolics, and styrenics. 

Although epoxies dominate the thermoset fracture literature, work has been reported on other systems, e.g., polyester resins, phenol-formaldehyde compounds, peroxide cured polystyrene, and highly crosslinked polyurethanes. In general, these materials exhibit fracture behaviors similar to epoxies, and suggest that thermosets, as a class of materials, display characteristic crack growth properties. 

In this book I have confined discussion to those polymeric materials which are cured by chemical reaction and which have found widespread application in the construction industry. As such, the book covers materials based on epoxies, polyurethanes, silicones, polysulphides, alkyds and polyesters. In addition, there is a chapter on hybrid polymer systems and one on acrylics. It is true that acrylic emulsions are not strictly thermosetting polymer systems, but their widespread use and importance made their exclusion difficult. These materials find use as coatings, sealants, adhesives, grouts, flooring compounds, repair compounds and waterproofing agents. 

THERMOSETTING POLYMERS IN CONSTRUCTION APPLICATIONS 4.10 Polyurethane leak sealers and crack-injection systems... 

Although there is considerable published literature on the relation of polyurethane properties to their chemical and physical structures, considerably less has appeared concerning the detailed nature of urethane polymerization. The thermoset nature of the classical polyurethane systems, which has provided fewer opportunities and thus less scientific interest for the study of the intermediate stages and course of urethane polymerization, likely helps account for this. 

Published information on urethane polymerization detail largely concerns thermoset urethane elastomers systems.4 13 In particular, the work of Macosko et. al. is called to attention. The present paper supplements this literature with information on the full course of linear thermoplastic urethane elastomer formation conducted under random melt polymerization conditions in a slightly modified Brabender PlastiCorder reactor. Viscosity and temperature variations with time were continuously recorded and the effects of several relevant polymerization variables - temperature, composition, catalyst, stabilizer, macroglycol acid number, shortstop - are reported. The paper will also be seen to provide additional insight into the nature and behavior of thermoplastic polyurethane elastomers. 

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