Corrosion-Resistant Polyester Resins Based on Eastman TMPD Glycol eastman
Contents Introduction....................................... Resin Preparation, Physical Properties, and Cure............. Resin Synthesis.................................. Notes on Curing.................................. Field Testing Pipes.................................. Testing Castings.................................... Summary.........................................
Introduction In the corrosion-resistant equipment industry, products are engineered to withstand the attack of extremely harsh environmental products such as sulfuric acid, hydrochloric acid, and hypochlorite solutions. Unsaturated polyester resins have become widely accepted in this industry because of their ability to prevail in such conditions without the degradation usually evident in products manufactured from metals, such as steel and aluminum.the resulting composite materials can be found in storage tanks, process tanks, pipes, etc. The branched, asymmetrical structure of TMPD glycol permits the preparation of noncrystalline polyesters. A sterically hindered secondary hydroxyl group and the hydrophobic nature of this glycol combine to contribute outstanding performance and resistance to acids, alkali, and other corrosive environments. The bulky molecular structure prevents the close packing of resin molecules, imparting lower density to unsaturated polyester resins in comparison with PG-based formulations. This provides the advantage of allowing a higher number of parts to be produced per unit weight of resin. The highly hindered secondary hydroxyl group of TMPD glycol does react more slowly during resin synthesis than do primary or less hindered secondary hydroxyl groups. As a result, special synthetic considerations are required to produce resins that provide the stated performance levels. Eastman recommends the use of a synthesis catalyst and a cook stabilizer to facilitate the synthesis of TMPD glycol-based resins. This market consists of both relatively low-cost, general-purpose corrosion resistant resins produced from propylene glycol (PG), isophthalic acid (PIA), and maleic anhydride (MA); and premiumquality resins based primarily on either bisphenol A (BIS A), vinyl ester (VE), or halogenated (HAL) unsaturated polyester (NPG glycol/chlorendic anhydride/ma) formulations. Laboratory evaluations have demonstrated many advantages of TMPD glycol in corrosion-resistant applications. However, for improved processability and cure characteristics, resin formulations should consist of a blend of TMPD glycol and PG with PIA/MA rather than using TMPD glycol as the sole glycol component. HO Unsaturated polyester resins based on TMPD glycol provide superior corrosion resistance in comparison to general-purpose resins and have other performance advantages that are useful in the fabrication of corrosion-resistant products. In addition, TMPD glycol-based polyesters are more economical than premium-quality formulations while providing comparable performance. TMPD Glycol OH OH OH Propylene Glycol
Resin Preparation, Physical Properties, and Cure Table Composition and Physical Properties of Laboratory- Prepared Unsaturated Polyesters TMPD Glycol/ Physical Properties PG/PIA a //MA b PG/PIA//MA Glycol weight ratio 7/ Glycol excess, mole % 0 0 Acid molar ratio, sat:unsat acids c : : Maleic content, wt % c 9 6 Acid number 0 0 Molecular weight, M n,00,600,00,600 Viscosity, Gardner U V V Viscosity in % styrene, cp 00 600 Color, Gardner Density in 0% styrene, kg/l (lb/gal).0 (8.7).09 (9.) Typical reaction time, h Catalyst, butylstannoic acid, wt % 0. a Manufactured by Eastman Chemical Company. b Double slash indicates first stage reactants and second stage reactants. c To maintain comparable maleic content in each of the resin formulations, it is necessary to adjust the acid molar ratios due to the higher molecular weight of TMPD glycol compared with PG (6. vs. 76.0, respectively). Resin Synthesis. Purge with nitrogen and charge first stage reactants to a reactor equipped with a heating mantle, agitator, partial condenser, temperature probe, water trap, and total condenser. Refer to Eastman publication N-.. Slowly melt contents and increase temperature to 00 C.. Process at 00 C until an acid number of is reached.. Cool to 80 C and add maleic anhydride.. Reheat to 00 C and process to an acid number of. 6. Cool to 0 C and rapidly add styrene monomer inhibited with 00 0 ppm hydroquinone. For the TMPD glycol-based formulation, a catalyst (0.% butylstannoic acid) was also added.
Notes on Curing A copromoter should always be used for roomtemperature curing of resins based on TMPD glycol. DMA (N,N-dimethylaniline) and DMAA (N,N-dimethylacetoacetamide) have been found to be effective copromoters when used with cobalt promoters (refer to Eastman publications GN-96, N-, and N-7). It is important to note that the cure window for maximizing the physical properties of fabricated equipment is more narrow for TMPD glycol-based resins than for resins based on PG. The additional time required to optimize the cure for these resins will pay significant dividends in terms of performance of the equipment produced. Some cure systems for TMPD glycol-based resins are shown in Table. Table Room-Temperature Cure Systems for Unsaturated Polyester Resins Based on TMPD Glycol/PG/PIA//MA TMPD Glycol/PG/PIA//MA Cure Systems Promoters, wt % a Cobalt octoate (6% Co) 0. 0. 0. Copromoters, wt % DMA 0. 0. Eastman DMAA 0. Catalyst, wt % MEKP.0.0. Inhibitor, ppm Eastman Hydroquinone (HQ) 0 00 0 Eastman Mono-t -butylhydroquinone 0 00 0 (MTBHQ) Properties Gel time, min 9 Time to peak exotherm, min 0 8 7 Peak exotherm, C ( F) 79 () 8 (6) 88 (70) a Based on total resin weight.
Field Testing Pipes Fiberglass reinforced pipe samples were prepared by a fabricator of commercial equipment using the experimental TMPD glycol/pg/pia//ma resin, a commercial PG/PIA//MA, and a commercial BIS A resin. The pipe samples were installed in a feed line from a chemical manufacturing process to a waste treatment facility at Eastman. The feed line provided an extremely severe environment for testing. The line carried a strong aqueous solution of sulfuric and hydrochloric acids containing small amounts of low molecular weight organic solvents, dissolved gases such as sulfur dioxide, and acid salts at temperatures varying from to 9 C (8 to 00 F). This environment would be considered too corrosive for metal pipes. After 6 months exposure, the pipe sections were removed and examined. The results indicated the formulation based on TMPD glycol provided better performance than formulations based on either the general-purpose or the premium-quality corrosion-resistant resin. Pipe Samples (6 Months Exposure) TMPD glycol/pg/pia These in-service test results agree with laboratory data on unreinforced castings that unsaturated polyester resins based on TMPD glycol/pg/pia//ma provide better performance than commonly used corrosion-resistant resins. PG/PIA BIS A
Testing Castings The corrosion resistance of unreinforced castings was evaluated by determining the percentage of original flexural strength retained after accelerated aging in various chemical environments for specified test intervals. The castings were prepared in the laboratory to 8-inch thickness and cured for hours at 70 C (8 F), hour at 00 C ( F), and hour at 0 C (0 F) using 0.% benzoyl peroxide as a catalyst. Note: Elevated temperature cures generally do not require the use of copromoters. The overall corrosion resistance of the castings is shown in Figure. The castings prepared with resins based on TMPD glycol were found to have excellent resistance to corrosive environments. These samples provided better flexural strength retention than samples prepared with the PG/PIA//MA resin in most environments tested. The TMPD glycol/pg/pia//ma resin exhibited favorable strength retention when compared with the commercial formulations as well. Figure Flexural Strength Retention of Castings (6 Months Exposure). wt % Sodium Hypochlorite @ C (.6 F) wt % Sulfuric Acid @ 99 C (0. F) wt % Hydrochloric Acid @ 99 C (0. F) wt % Sodium Hydroxide @ 66 C (0.8 F) Distilled Water @ 9 C (99. F) 0 0 0 60 80 00 0 0 Vinyl ester (VE) Halogenated unsaturated polyester (HAL) Bisphenol A (BIS A) Propylene glycol/ isophthalic acid (PG/PIA) TMPD glycol/propylene glycol/isophthalic acid (TMPD/PG/PIA) Summary % Retention Data from this study demonstrates that resins based on TMPD glycol offer excellent corrosion resistance properties that exceed the performance of both low-cost, general-purpose corrosion-resistant resins and of more expensive, premium-quality resins in many chemical environments. High performance and low cost makes TMPD glycol an attractive choice for manufacturers and fabricators of corrosion-resistant polyester-based composites.
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