ELIMINATION OF COPOLYMER IN POLYVINYL CHLORIDE PLASTISOLS USING HIGH-SOLVATING DIBENZOATE PLASTICIZERS

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1 ELIMINATION OF COPOLYMER IN POLYVINYL CHLORIDE PLASTISOLS USING HIGH-SOLVATING DIBENZOATE PLASTICIZERS Deirdre K. Newton, William D. Arendt, and Emily L. McBride Emerald Kalama Chemical, LLC - Kalama, WA High-solvating dibenzoate plasticizers are already known for their ability to reduce gelation and fusion temperatures relative to formulas with general purpose plasticizers. [1] In this evaluation, plastisols were prepared to compare different PVC resins, homopolymer versus copolymer, as well as different plasticizers, general purpose versus high solvators. Viscosity aging was evaluated at room temperature and 4 C to determine the storage stability of each formulation. Fusion characteristics and mechanical properties were compared by gel/fusion and different processing temperatures. This data was used to demonstrate that high-solvating dibenzoate plasticizers can successfully be used to reduce fusion temperature and increase storage stability, which enables formulators to replace copolymer with homopolymer while retaining processability, improving certain mechanical properties, and reducing cost. INTRODUCTION/BACKGROUND Dibenzoate plasticizers are used in a variety of polymers, but a key market in which the use of dibenzoates yields many advantages is flexible vinyl. Plastisols, which are mixtures of PVC resin dispersed in plasticizer that will fuse into a plastic when heated. The high polarity of benzoates leads to them being high-solvators for PVC, and their unique properties and processing advantages make them attractive for use in certain products. High-solvation means gelation and fusion will happen at a lower temperature than with general purpose plasticizers, which increases speed of production and decreases energy usage, as well as increasing the size of the processing window. In addition, dibenzoates can impart other beneficial properties, such as increased stain and UV resistance, and better foam blow ratios and foam quality. [1] Currently, many industrial applications of plastisols use PVC/vinyl acetate copolymer dispersion resin. Homopolymer resins are less expensive, but there are certain benefits to using copolymer resins instead. One of the main reasons to use copolymer resins with general purpose plasticizers is for lower fusion temperature. This enables faster and more energy efficient processing which decreases the processing cost and increases output. [2]. However, the downside is that copolymers are affected by elevated storage temperature and generally have a lower tensile strength compared to homopolymers. Other properties that have effects on fusion of the plastisol are molecular weight of the resin and percent vinyl acetate content. Increasing vinyl acetate content reduces gelation and fusion temperature, but also increases paste viscosity and decreases viscosity stability. [3] This is because vinyl acetate is an internal plasticizer: it essentially softens PVC by affecting crystallite formation, resulting in a lower T g and making the resin more susceptible to solvation by plasticizers. [4] SPE ANTEC Anaheim 217 / 2542

2 The goal of this paper is to demonstrate that using high-solvating dibenzoate plasticizers, either alone or in conjunction with general purpose plasticizers, enable a move away from copolymer resin to homopolymer resin, while still retaining processability and final physical properties. This will be explored by comparing the rheology and physical properties of various combinations of resins and plasticizers, as well as homopolymer formulations with blends of plasticizers. Materials EXPERIMENTAL Three resins and five plasticizers were used in this study. The PVC homopolymer was a dispersion resin D5-22 as per ASTM D1755. Two different copolymer dispersion resins were used: a 4% vinyl ester copolymer, and a 7% vinyl acetate copolymer. The general purpose plasticizers used were diisononyl phthalate (DINP), dioctyl terephthalate (DOTP), and 1,2-cyclohexane dicarboxylic acid diisononyl ester (DIDC). The high solvating plasticizers used were: a triblend of dipropylene glycol dibenzoate, diethylene glycol dibenzoate, and propylene glycol dibenzoate (975P), and a diblend of dipropylene glycol dibenzoate and diethylene glycol dibenzoate (85P). A calcium/zinc PVC heat stabilizer was used. Plastisol and Vinyl Preparation The formulas for all the plastisols studied can be found in Tables 1 and 2 in the Appendix. Plasticizer and heat stabilizer were added to a Hobart mixer and mixed for 3 seconds on speed 1, then PVC resin was slowly added and mixed on speed 1 for 1 minutes. Samples were then degassed under vacuum for 2 minutes after reaching ~1 mmhg. Each formulation was split evenly into two containers, one of which was stored at ambient temperature (23 C) and the other was stored at elevated temperature (4 C). Viscosity and Gel/Fusion Low shear viscosity measurements were collected per ASTM D1824, with modifications. Measurements were taken at 2 RPM 3 seconds after starting the spindle rotation, and the spindle was often spindle 4 but was selected to keep the torque in the 1-9% range for accuracy. The measurements were taken initially, after 1 day, after 3 days, and after 7 days of aging. High shear viscosity measurements were collected using shear rate ramps on a TA Instruments AR2ex Rheometer equipped with a 2mm parallel plate geometry and a Peltier plate set at 25 C. The shear rate ramped from -1 s -1 and the geometry gap was set to 2 µm. Both high shear and low shear viscosity measurements were collected for both storage conditions, room temperature and elevated temperature at 4 C. Gel/fusion testing was also performed on the TA Instruments AR2ex Rheometer with the 25mm parallel plate environmental test chamber geometry. The plate gap was set at 6 µm and it was oscillated at a frequency of 1 rad/s while the temperature was ramped at a rate of 5 C/min from 4 to 2 C. Fusion SPE ANTEC Anaheim 217 / 2543

3 After the viscosity and gel/fusion testing was completed, the formulations stored at ambient temperature were fused into vinyl sheets in a Mathis LabDryer oven. The parameters were: a wet drawdown thickness of 49 mils, fan speed of 75 RPM, and bake time of 3 minutes. These sheets were used for tensile strength and hardness testing. Tensile Strength Tensile testing was performed per ASTM D638 for nonrigid plastics using Type IV test specimens and a pull rate of 2 in/min. Hardness Hardness was determined in accordance with ASTM D224 using a PTC Instruments Type A Durometer Model 36L. DISCUSSION A tensile ladder was performed on each formulation, with specimens fused every 2 C from 12 to 2 C in order to determine tensile strength development, as seen in Figure 2. The results showed that the 16 C temperature was the lowest temperature at which certain formulations reached maximum tensile strength. Figure 5 shows the tensile strength at 16 C for all formulations. The dibenzoates when blended with the GP plasticizers greatly improve fusion as shown by the tensile strength comparison to the corresponding 1% GP homopolymer formulations. The 7/3 dibenzoate/gp blends had tensile strengths comparable to the corresponding 7% copolymer formulations. Because fusion occurs over a range of temperatures, it is often not necessary to reach final fusion to adequately process plastisols and impart desirable mechanical properties. [5] However, comprehensive gelation and fusion data can still be used to compare formulations. Figure 1 compares the direct gel/fusion rheometer data of all formulations, and Table 3 summarizes the final fusion temperatures and moduli of all formulations, which is based on the crossover of G and G after peak G. Copolymer and dibenzoate formulations had the lowest fusion temperature with highest modulus, but much poorer storage stability as seen in the Brookfield viscosity results in Figure 4. The same overall trend is observed in Figure 1 as was observed in the tensile ladder, which is that the addition of dibenzoates to a homopolymer/gp system greatly improved fusion characteristics. Overall, within a set of formulations with the same resin, the dibenzoate formulations had lower fusion temperatures and higher modulus values compared to general purpose (GP) plasticizers. Higher modulus values, as seen in Table 3, indicate greater mechanical strength, which then corresponded well to the tensile strength results in Figure 2. The 7/3 dibenzoate/gp blends, the lowest of which fused at 171 C, were comparable to the 7% copolymer/gp formulations which ranged from C. As expected, the copolymer formulations stored at elevated temperature showed poorer storage stability. The more highly solvated formulations had elevated temperature storage stability that was magnitudes higher. Copolymer formulations with dibenzoate plasticizer had gelled too much to take Brookfield viscosity after only one day in the oven, and homopolymer formulations made it to day 3 before reaching the same point, which is SPE ANTEC Anaheim 217 / 2544

4 represented by the arrows going off the graph in Figures 6 and 7. Storage stability is the primary reason why homopolymer formulations can be optimized using blends of dibenzoates and GP plasticizers. Blending the two dramatically increases the storage stability and reduces the fusion temperature. CONCLUSIONS Dibenzoate plasticizers allow for more formulation choices based on required properties. It has been demonstrated that they can be used to replace copolymer resin with homopolymer resin for reduced cost. Issues of storage stability and viscosity can be solved by optimization of the dibenzoate/gp plasticizer blend. ACKNOWLEDGEMENTS The authors of this paper would like to acknowledge Emerald Kalama Chemical for permission to submit this paper. DISCLAIMER The information contained herein is believed to be reliable, however is based upon laboratory work with small scale equipment and does not necessarily indicate end-product performance. Because of variations in methods, conditions and equipment used commercially in processing these materials, Emerald makes no representations, warranties or guarantees, express or implied, as to the suitability of the products for particular applications, including those disclosed, or the results to be obtained. Full-scale testing and endproduct performance are the responsibility of the user. Emerald Performance Materials shall not be liable for and the customer assumes all risk and liability for use and handling of any materials beyond Emerald s direct control. Nothing contained herein is to be considered as permission, recommendation nor as inducement to practice any patented invention without permission of the patent owner. REFERENCES [1] Grossman, Richard F., ed. Handbook of Vinyl Formulating. 2nd ed. Hoboken, NJ: John Wiley & Sons, 28. [2] Garcia, L. G. Fusion of PVC-Vinyl Acetate Copolymer Plastisols. J Vinyl Addit Techn 3, no. 3(1981): [3] Johnston, Christian W., Brower, Charles H. Effect of Acetate Content on Physical Properties of Copolymer Plastisol Resin. SPE Journal (1967): [4] Nass, Leonard I., and Charles A. Heiberger, eds. Encyclopedia of PVC. 2nd ed. Vol. 1. New York: Marcel Dekker, [5] Daniels, Paul H., Brofman, Carl M., and Harvey, Gary D. Meanginful Evaluation of Plastisol Gelation and Fusion Temperatures by Dynamic Mechanical Analysis. J Vinyl Techn 8, no. 4(1986): SPE ANTEC Anaheim 217 / 2545

5 APPENDIX Table 2: 1% Plasticizer Formulations Material PHR by weight PVC dispersion resin 1 Plasticizer 7 Ca/Zn heat stabilizer 3 Table 1: GP/High-Solvator Formulations Material 7/3 GP/HS (PHR) 3/7 GP/HS (PHR) PVC dispersion resin 1 1 GP Plasticizer High-solvating plasticizer Ca/Zn heat stabilizer 3 3 Table 3: Gel/Fusion, G'xG" in Ascending Order by Temperature Sample Temp ( C) G (Pa) 7% co/975p % co/85p % co/dinp % co/dotp % co/didc homo/85p:dotp % co/975p % co/85p homo/975p homo/85p homo/975p:dotp homo/975p:dinp homo/85p:dinp % co/dinp homo/dotp:85p homo/dotp:975p homo/dinp:85p homo/dinp:975p % co/didc homo/dinp homo/dotp homo/didc % co/dotp SPE ANTEC Anaheim 217 / 2546

6 Tensile STrength (psi) Storage Modulus, G (Pa) Temperature ( C) homo/85p homo/975p 4% co/dinp homo/85p:dotp homo/85p:dinp homo/975p:dotp homo/975p:dinp 4% co/dotp homo/dotp:975p homo/dotp:85p homo/dinp:85p homo/dinp:975p 7% co/dinp homo/dinp homo/dotp 7% co/dotp Figure 1: Gel/Fusion Comparisons of 1% Plasticizer Formulation and 7/3 Blends Temperature ( C) DINP 975P 85P DOTP DIDC DOTP/85P DOTP/975P DINP/85P DINP/975P 85P/DOTP 975P/DOTP 975P/DINP 85P/DINP Figure 2: Homopolymer tensile strength development: 3 min fuse time, 75 rpm fan speed. SPE ANTEC Anaheim 217 / 2547

7 Tensile Strength (psi) Viscosity (mpa s) Viscosity (mpa s) Initial 7 day Total increase Figure 3: Room temperature storage stability at 23 C, homopolymer. 7/3 order Note: Naming convention for blends is always in DINP 975P 85P DOTP DIDC DINP 975P 85P DOTP DIDC Initial 7 day Total increase 4% vinyl ester 7% vinyl acetate Figure 4: Room temperature storage stability at 23 C, copolymer Homopolymer 4% Copolymer 7% Copolymer Figure 5: Tensile strength of plastisols fused at 16 C. SPE ANTEC Anaheim 217 / 2548

8 Viscosity (mpa s) Viscosity (mpa s) Initial 7 day Total increase 2 Figure 6: Elevated temperature storage stability at 4 C, homopolymer DINP 975P 85P DOTP DIDC DINP 975P 85P DOTP DIDC Initial 7 day Total increase 4% vinyl ester 7% vinyl acetate Figure 7: Elevated temperature storage stability at 4 C, Copolymer SPE ANTEC Anaheim 217 / 2549