Ambient temperature-cured solution

Ambient Temperature Cured Solution Epoxy Coatings... 

In the past chemical cure linings have been employed on a wide scale. These linings, usually based on natural rubber or acrylonitrile-butadiene rubber consist of a standard lining compound with a chemical activator such as dibenzylamine incorporated in the formulation. Prior to the application of the lining to the substrate, the individual sheets of rubber are dipped or brush coated with carbon disulphide or a solution of a xanthogen disulphide in a solvent. The carbon disulphide or xanthogen disulphide permeates the rubber and combines with the dibenzylamine to form an ultra-fast dithiocar-bamate accelerator in situ, and thus the rubber rapidly vulcanises at ambient temperature. 

The reaction was carried out at 100°C for about two hours until the theoretical isocyanate content, as determined by the di-n-butylamine titration method (27), was reached. The PU prepolymer with or without tertiary amine nitrogen groups was dissolved in dry MEK to obtain a prepolymer solution of 30-40% solids. It was then mixed with a mixture of 1,4-BD/TMP (4 1 by equiv. ratio) at an NCO/OH = 1.05/1.0 ratio in the presence of T-12 catalyst (0.05% based on total weight). The reaction mixture was cast in a metal mold treated with a release agent at ambient temperature. After standing 3-5 hours at room temperature, the mold was placed in an oven and post-cured at 100°C for 16 hours. The samples were then conditioned in a desiccator for one week before testing. 

Catalyzed Pot Stability. A sample of the above BA/HHA/25X ABDA copolymer In butanol/toluene was catalyzed with IX Nacure (S/S). The viscosity was observed qualitatively and an Initial aliquot was drawn down as a 2 mil film on glass and cured (150 C/3 min or room temperature for 35-45 d). After 24 h at ambient temperature one equivalent of methanol based on ABDA was detected by GLPC In the solution. After 5 d at ambient and 24 h at 40 C, two equivalents of HeOH were present. Indicating complete alcohol exchange. The solution polymer showed no thickening. Films were also drawn down with these samples and evaluated (Table VI). 

Resorcinol differs from other phenols in that it reacts readily with formaldehyde under neutral conditions at ambient temperature. To make stable adhesives, which can be cured at the point of use, they are prepared with less than a stoichiometric amount of formaldehyde. About two thirds of a mole of formaldehyde for each mole of resorcinol will give a stable resinous condensation product. The resin is formed into a liquid of convenient solids content and viscosity. Such solutions have infinite stability when stored in closed containers. Glue mixes formed at the point of use from these solutions, on addition of paraformaldehyde-containing hardeners, will have a useful life of several hours due to two principal factors (1) the paraformaldehyde depolymerizes to supply monomeric formaldehyde at a slow rate, as determined by the pH (2) the availability of the formaldehyde is also controlled by the kind and amount of alcohol in the solvent. Formaldehyde reacts with the alcohol to form a hemiacetal. This reaction is reversible and forms an equilibrium which exerts further control on the availability of the formaldehyde. 

CHARACTERIZATION. Melting points were determined on an E. I. DuPont Series 99 Thermal Analyzer at 20°C/min. Inherent viscosities of polyamic acid solutions were obtained at a concentration of 0.5% (w/w) in DMAc at 35°C. Glass transition temperatures (T ) of the fully cured polymer films were measured by thermomechanical analysis (TMA) on a DuPont 943 Analyzer in air at 5°C/min. Films fully-cured at 300°C were tested for solubility at 3-5% (w/w) solids concentration in DMAc,N,N-dimethylformamide (DMF), and chloroform (CHCl-j). Solubilities at room temperature were noted after periods of 3 hours, 1 day and 5 days. Refractive indices of 1 mil thick films were obtained at ambient temperature by the Becke line method (11) using a polarizing microscope and standard immersion liquids obtained from R. P. Cargille Labs. 

Di(tert Butyl)p-cresol techn. pure powder 40% solution in xylene (SETA flash point 30) Prolongs (up to weeks/months) shelf life - gel time of resin + peroxide - at ambient temperature effect on cure times diminishes with rise in temperature efficient with many types of resin and peroxide fgHI... 

The same results were obtained by Ghorab and Kisher [158]. Also Sylla [159] found the reduction of ettringite content in cement pastes after 3 h of thermal treatment at temperature of 60 °C this phase disappears almost entirely after this period when the temperature of curing rises to 80 °C. The same results were found by Odler et al. [160]. It found also good relation with the composition of solution, which in the pastes subjected to thermal treatment at temperature of 90 °C have a diSerent sulphate ions concentration (Fig. 6.38). The concentration of these ions is maintained on the high level after 28 days of paste matured in water and is quicker reduced after this period [151]. However, even after 90 days it is four times higher than in the paste cured all the time in water at ambient temperature. 

TPAs are high MW acrylic copolymers supplied in organic solvents. These copolymers are typically prepared from monomers such as methyl methacrylate, styrene, or n-butyl acrylate. The selection of solvent is dictated by solubility of the resin, solution viscosity, evaporation rate, type of final coating for which it will be used, and cost. TPAs are generally used in systems that cure at ambient temperature without the need for cross-linkers. Therefore, such resins are designed with specified T so as to produce dried films with... 

The free-standing films were made by casting DMAc solutions of the poly(amic acid)s onto a dust-free glass plate and vacuum drying at ambient temperature until tack-free. Films were cured under a dynamic nitrogen atmosphere at 30 C for 0.5 h and at 100,200, 300 C each for 1 h. In situ FTIR spectra (using a heated IR cell) confirmed the cyclization process. Disappearance of peaks at ca 1220 and 1544 cm were diagnostic for reaction of the amide and add residues while appearance of new peaks at ca 1365 and 1775 cm confirmed imide formation. 

Water-dispersible resins contain carboxyhc groups which are neutralized using base or amine compounds. This solubilizes the resin in solution and also promotes pigment wetting. Film formation occurs by the evaporation of volatiles foUowed by cross-linking through ambient cure oxidative reactions or elevated temperature reactions. Solvents, most commonly glycol ethers, are used to promote film formation and improve film quahty. 

Ultra thin microporous carbon films are derived via the pyrolysis of phenolic precursors. The latter can be prepared from resorcinol-formaldehyde resins using a base catalyst. After several hours at 50°C of curing, the solution forms a stable polymeric film. Followed by a solvent exchange and ambient pressure drying, the film is pyrolysed in argon atmosphere at temperatures above 800°C. The result is an electrically conducting polymeric carbon film, the structure of which resembles the organic precursor, but shows microporosity in addition. Hereby, films with thicknesses of > 5 microns and sufficient mechanical stability can be made. 

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