Styrene-Butadiene Copolymers Plastics Technical Center Report #9 K-Resin SB Copolymer/Crystal Polystyrene Sheet Property Modification with High Impact Polystyrene INTRODUCTION. Many sheet extruders are using K-Resin styrene-butadiene copolymer in machine side blends with crystal polystyrene. The K-Resin provides excellent toughness, and the polystyrene provides rigidity and economics. As the amount of crystal polystyrene in the blend is increased, the impact properties and performance of the sheet are diminished. This study evaluates the effect on physical properties of the sheet when low levels of high impact polystyrene HIPS are added to the blend. PROCEDURE. K-Resin/crystal polystyrene blends containing % K-Resin were compared in this study. Chevron 371, with a nominal 18 MF, polystyrene resin was used in this trial. Dow s high impact polystyrene grade, XL-88, was chosen as the HIPS impact modifier. It is a nominal 5 melt flow and has a notched Izod impact strength of 3 ft-lbf/in. The level of HIPS in the blend ranged from.5 to %. Samples were prepared by dryblending of the components together then repelletizing the blend. One set of samples of the 5/5 blends was dryblended only to determine if there was a significant difference in sheet properties of compounded vs. noncompounded samples. The blended samples were extruded into mil sheet on a 3 1 / inch NRM extruder and injection molded into test specimens for evaluation of physical properties. These results are shown in the accompanying Tables 1 8. RESULTS. Sheet strength was measured by both falling dart and a modified gardner impact test method. The two tests yielded similar results. They showed a substantial increase in impact of all the sheet samples to which high impact polystyrene was added. At the lowest level of HIPS addition,.5%, significant improvement in sheet strength was achieved. However, sheet strength values did not increase much as higher levels of HIPS were added. This is highlighted in Figures 1 and. Haze values increased significantly as higher levels of HIPS were added. Sheet clarity remained good when.5% HIPS was added to the blend. The haze development was most easily seen in the thicker injection molded specimens (15 mils), and worst in blends containing higher levels of crystal polystyrene (See Figures 3 and ). The dryblended pellets and repelletized samples produced sheet with very similar impact properties. The haze values in the sheet were also very similar, but in the thicker injection molded specimen, the repelletized samples had better clarity. This is the result of better mixing in the sheet line than in the injection molding process. HIPS also demonstrated improving antiblocking characteristics of the blended sheet. This occurred at levels as low as.5% HIPS. 1
Styrene-Butadiene Copolymers Table 1 Properties of / K-Resin/GPPS mil Blended Sheet Modified with Dow XL 88 HIPS Property.5.75 1. 1.5. Haze, % 3. 5.3.9.9 5.8 7.1 Light Transmission, % 89. 89. 89.3 89.1 89. 88.9 Dart Drop, g/ in 3 599 57 58 35 75* 75 Tensile Yield, psi MD 75 5 3 39 5 TD 5 55 5 5 Tensile Break, psi MD 35 3 35 3 3 35 TD 35 3 5 55 15 5 Elongation, % MD 9.7 18.3 8.7 15. 3.3 17.7 TD 1..7 1.7 31 1.7 15.7 Oil Bath Shrinkage, % MD 7. 7. 3.3 9.7 35.1 37.9 TD -. -. -5. -5.8 Hunter, Color b...1...1 -b -7. -7. -7.8-7.9-8.1-8.5 Modified Gardner Impact, cm/kg.7.3..8.83.5 * Large variation Table Properties of 5/5 K-Resin/GPPS mil Blended Sheet Modified with Dow XL 88 HIPS Property.5 1.. Haze, %.. 11. 11.5 Light Transmission, % 89.3 89.1 87. 87.9 Dart Drop, g/ in 3 5 5 35 Tensile Yield, psi MD 5 37 15 TD 85 55 85 Tensile Break, psi MD 5 35 31 3 TD 5 5 55 55 Elongation, % MD 7. 1. 9. 7.7 TD 7... 3.7 Oil Bath Shrinkage, % MD.5 9.1 8. 7. TD -.3 -.9 -.1 -. Hunter, Color b.1. 1.9 1.7 -b -9.8-9. -1. -11. Modified Gardner Impact, cm/kg.75.1.15.
Table 3 Properties of / K-Resin/GPPS mil Blended Sheet Modified with Dow XL 88 HIPS Property.5 1.. Haze, % 5. 5.1 13.3 11.3 Light Transmission, % 87.9 88.8 87.1 87. Dart Drop, g/ in 19 99 71 57 Tensile Yield, psi MD 37 39 395 TD 35 95 31 3 Tensile Break, psi MD 33 31 3 3 TD 95 8 3 85 Elongation, % MD.7 5. 7. 1.3 TD 3.3. 3.. Oil bath Shrinkage, % MD 3. 31. 7.3 7.7 TD -.9-5. -.3-3.9 Hunter, Color b 1.9 1.9 1.7 1.5 -b -13. -11.5-1.3-1.7 Modified Gardner Impact, cm/kg.5 1.5 1.5 1.95 Table Properties of 5/5 K-Resin/GPPS mil Blended Sheet Modified with Dow XL 88 HIPS (Dry Blended Only) Property.5 1.. Haze, % 3.3 5. 11. 1.3 Light Transmission, % 88.8 88. 87. 87.7 Dart Drop, g/ in 3 5 7 Tensile Yield, psi MD 39 15 38 TD 85 8 8 85 Tensile Break, psi MD 39 33 335 95 TD 5 5 55 Elongation, % MD.7..7 1. TD 3.3 1. 7.7 1.7 Oil Bath Shrinkage, % MD 1.1 3. 3.5 3.8 TD -7.1-5.9-5.1-3. Hunter, Color b.. 1.8 1.8 -b -1. -1.3-1.9-11.3 Modified Gardner Impact, cm/kg.5 1.95 1..5 3
Styrene-Butadiene Copolymers Table 5 / K-Resin/GPPS Blends Injection Molded Specimen Modified with Dow XL 88 HIPS Property.5.75 1. 1.5. Haze, % 1.1.5.8 5. 3.1 37. Light Transmission, % 83.7 81.3 81. 81. 79.7 79.5 Tensile Yield, psi 9 5 55 55 55 Elongation, % 1 19 3 17 Flexural Modulus, psi 9,7 98,5 99,5 8,5 91, 9,5 Flexural Yield Strength, psi 7 7 71 7 95 Notched Izod, RT, 1/8", ft-lbf/in.18.18.17.19.19.1 Hunter, Color b 7.. 5.8. 5. 5.1 -b -15.7-1.3-17. -1.5-1.3-1. Flow Rate, g/1 min 1.1 1.5 1.3 1. 1.3 1. Table 5/5 K-Resin/GPPS Blends Injection Molded Specimen Modified with Dow XL 88 HIPS Property.5 1.. Haze, % 1.7 1.7 3.9. Light Transmission, % 8.1 79.3 78. 7. Tensile Yield, psi 5 8 5 5 Elongation, % 1 18 18 1 Flexural Modulus, psi 319,5 31,1 31,9 3, Flexural Yield Sstrength, psi 7 7 7 7 Notched Izod, RT, 1/8", ft-lbf/in..1.1.1 Hunter, Color b.. 3.. -b -19. -18.7-18. -17.7 Flow Rate, g/1 min 11.7 11.3 11. 11.5
Table 7 / K-Resin/GPPS Blends Injection Molded Specimen Modified with Dow XL 88 HIPS Property.5 1.. Haze, % 17.1 8. 3. 5. Light Transmission, % 77. 75.1 75.5 73.7 Tensile Yield, psi 51 75 5 7 Elongation, % 1 18 1 Flexural Modulus, psi 31,5 337, 335,1 33,15 Flexural Yield Strength, psi 785 77 77 775 Notched Izod, RT, 1/8", ft-lbf/in.1...1 Hunter, Color b 3.1.1.9 -.1 -b -19. -18. -18.8-17.9 Flow Rate, g/1 min 1.9 1.7 1.8 1.7 Table 8 5/5 K-Resin/GPPS Blends Injection Molded Specimen Modified with Dow XL 88 HIPS (Dry Blended Only) Property.5 1.. Haze, % 3.7 3.5 39. 5. Light Transmission, % 7. 7.1 7.8 7.3 Tensile Yield, psi 5 75 Elongation, % 18 18 17 18 Flexural Modulus, psi 31,5 31,75 315,5 31,1 Flexural Yield Strength, psi 735 735 7 77 Notched Izod, RT, 1/8", ft-lbf/in.1..18.19 Hunter, Color b 3.8. 1.. -b -17. -1.8-17. -1. Flow Rate, g/1 min 1. 1.8 1.3 1. CONCLUSIONS. Low levels of high impact polystyrene can significantly improve sheet impact properties of K-Resin/crystal polystyrene blend sheet. The HIPS also strengthens the sheet across the transverse direction, which makes the sheet more resistant to breakage. Adding.5 % HIPS to the sheet is approximately equivalent to increasing the K-Resin content by more than 1%. The amount of haze in the sheet increases as the percentage of HIPS is increased. Most blends should contain less than 1% HIPS to maintain maximum part clarity. Precompounding of the HIPS into the blend did not offer advantages in either impact or clarity of the blended sheet. 5
Styrene-Butadiene Copolymers Figure 1 Dart Drop Test Sheet 1 K-RESIN/GPPS / BLEND 1 K-RESIN/GPPS 5/5 BLEND DART DROP, gm/ in 8 3 599 57 58 55 75 DART DROP, gm/ in 8 3 5 5 35.5.75 1. 1.5..5 1.. 1 K-RESIN/GPPS / BLEND 1 K-RESIN/GPPS 5/5 DRY BLEND DART DROP, gm/ in 8 19 99 71 57 DART DROP, gm/ in 8 3 5 7.5 1...5 1.. Figure Modified Gardner Sheet Impact MODIFIED GARDNER IMPACT, cm/kg 3.5 3..5. 1.5 1..5 K-RESIN/GPPS / BLEND.7.3..8.83.5 MODIFIED GARDNER IMPACT, cm/kg 3.5 3..5. 1.5 1..5 K-RESIN/GPPS 5/5 BLEND.1.75.15..5.75 1. 1.5..5 1.. MODIFIED GARDNER IMPACT, cm/kg 3.5 3..5. 1.5 1..5 K-RESIN/GPPS / BLEND 1.5.5 1.5 1.95 MODIFIED GARDNER IMPACT, cm/kg 3.5 3..5. 1.5 1..5 K-RESIN/GPPS 5/5 DRY BLEND 1.95.5 1..5.5 1...5 1..
Figure 3 Haze Percentage Sheet 1 1 1 1 8 K-RESIN/GPPS / BLEND 3. 5.3.9.9 5.8 7.1 1 1 1 1 8 K-RESIN/GPPS 5/5 BLEND.. 11. 11.5.5.75 1. 1.5..5 1.. 1 1 1 1 8 K-RESIN/GPPS / BLEND 5. 5.1 13.3 11.3 1 1 1 1 8 K-RESIN/GPPS 5/5 DRY BLEND 3.3 5. 11 1.3.5 1...5 1.. Figure Haze Percentage Injection Molding K-RESIN/GPPS / BLEND K-RESIN/GPPS 5/5 BLEND 5 3 1.1.5.8 5. 3.1 37. 5 3 1.7 1.7 3.9. 1 1.5.75 1. 1.5..5 1.. K-RESIN/GPPS / BLEND 5. K-RESIN/GPPS 5/5 DRY BLEND 5. 5 5 3 17.1 8. 3. 3 3.7 3.5 39. 1 1.5 1...5 1.. 7
Styrene-Butadiene Copolymers