Styrolux Styrene-Butadiene Copolymer (SBC) Mechanical and Optical Properties

Transcription

1 Styrolux Styrene-Butadiene Copolymer (SBC) Mechanical and Optical Properties

2 Toughness, stiffness and clarity are key attributes of Styrolux Styrene-Butadiene Copolymer (SBC). Another significant property of Styrolux is easy blending with a variety of polymers, such as general-purpose polystyrene (GPPS), which results in cost-efficient production of transparent sheets and finished products with tailored combinations of properties. Tensile Performance stable, low-extensibility material with high tensile strength and low tensile strain at break. In contrast, the Styrolux curve has a flatter gradient, meaning lower stiffness. Once the yield point has been reached there is no rise in stress as tensile strain continues to increase. This very distinct deformation behavior leads to fracture as tensile strain increases further. This type of curve is characteristic of very tough materials. Because Styrolux 3G 55 has lower stiffness than Styrolux 656 C, the stress values on the curve are lower. Styrolux Compared to General-Purpose Polystyrene The Styrolux product line includes grades with various combinations of stiffness and toughness (Table 1). Product stiffness reduces as toughness increases. Values for modulus of elasticity (stiffness) and tensile strain at break (toughness) determined from the tensile test are important indicators for these properties. Stiffer products with higher modulus such as Styrolux 656 C are suitable for injection-molding applications. These higher stiffness products are not typically used in blends with GPPS. Tough to very tough grades such as Styrolux 684 D or Styrolux 3G 55 are used in extrusion to produce films or thermoformed sheet, since this is where extremely easy blending with GPPS is a prime requirement. Styrolux SBC Stiffness Modulus of elasticity (MPa) Toughness Tensile strain at break (%) 656 C D G 55 9 >3 GPPS Table 1: Guideline values for stiffness and toughness of Styrolux products compared with GPPS; measured by the ISO 527 tensile test. Stress-Strain Performance The stress-strain graph (Figure 1) by ISO 527 illustrates the performance of Styrolux compared with GPPS for short-term, single-axis tensile stress and low deformation rate. Alongside stiffness and toughness, the stress-strain curve here also indicates the yield stress and fracture energy, which is the area under the stressstrain curve. GPPS typically has a steep, almost straightline curve and fractures after very slight deformation. This characterizes GPPS as a stiff and dimensionally Mechanical Properties Stiffness in Blends with GPPS Styrolux is often blended with GPPS in extrusion applications. As GPPS content increases, the effect on stiffness (Figure 2) is an almost linear rise in modulus of elasticity or yield stress. This is particularly desirable for these applications. Toughness in Blends with GPPS In contrast to stiffness, the toughness of Styrolux/ GPPS blends decreases when GPPS is added. This decrease is a non-linear function of GPPS content. The reduction is somewhat smaller at lower blend levels. However, as GPPS level increases there is a very rapid drop-off in the toughness of the blend. This reduction in toughness can also be described using the tensile strain at break obtained from the tensile test (Figure 3). The sharp reduction in tensile strain at break when GPPS content in the blend is more than 4% can be seen. Blends with less than 2% of Styrolux show hardly any improvement in tensile strain at break. Tensile strain at break in the extrusion direction is generally relatively low a consequence of orientation of the rubber phase in Styrolux. Lamellar morphology of Styrolux in blends with GPPS parallel to the direction of extrusion reduces the amount of additional strain available on stretching in that direction. Depending on the Styrolux grade, blends from 3 to 8% of Styrolux with GPPS have proven successful in extrusion applications.

3 Impact Strength of Styrolux Products In contrast with the relatively low deformation rate in the tensile test, high deformation rates subject the test specimens to much more powerful fracture stresses. The Charpy (ISO 179) flexural impact test carried out on test specimens of the tougher Styrolux grades produces fractures only if the specimens have been previously V-notched (ISO 179/1eA) (Table 2). Flexural impact parameters determined on injectionmolded test specimens are higher than those for loworientation specimens, because the direction of stress is identical with the preferential direction of orientation. The flexural impact test is therefore mainly used for comparative evaluation of product toughness. Values in (kj/m2) Impact Strength ISO 179/1eU Notched Impact Strength ISO 179/1eA 656 C D 1 3 3G 55 nf 5 Table 2: Guideline values for impact strengths of Styrolux grades at 23 C; nf = no fracture. Multi-Axial Impact Strength Styrolux and High-Impact Polystyrene (HIPS) Stress under practical conditions is much more likely to be multi-axial with no preferential direction rather than mono-axial. The automated ISO penetration test measures this, with central impact on a flat surface of an extruded sheet or injection-molded plaque, for example. The fracture energy is the area below the forcedisplacement curve, and this shows that toughness is markedly higher for Styrolux grades than for comparable grades of high-impact polystyrene (Figure 4). Puncture Resistance on Sheets made from Styrolux/GPPS Blends Like tensile strain at break (see Figure 3), puncture resistance as a function of Styrolux/GPPS blending ratio reduces with increasing GPPS content. Figure 5 shows this fracture behavior for 1 mm sheet made from Styrolux 684 D/GPPS blends. Here it is clear that the oil-containing polystyrene grade PS 143 E gives increased toughness. Influence of Blend Components The mechanical properties of blends are affected both by the Styrolux used and by the GPPS grade used. Styrolux Grades The variation in properties of Styrolux/GPPS blends reflects the reduction in stiffness and associated increase in toughness within the Styrolux line. Styrolux 3G 55 has particular toughness efficiency properties in blends with GPPS. When comparison is made with conventional grades, such as Styrolux 684 D, Styrolux content in terms of the amount of SBS used can be reduced by up to a quarter in blends with GPPS, e.g. PS 158 K. These blends using Styrolux 3G 55 are just as stiff as conventional blends. Styrolux 3G 55 therefore helps to reduce costs of finished parts made from Styrolux/GPPS. GPPS Grades GPPS containing lubricant PS 143 E for example gives higher toughness values than oil-free GPPS grades such as PS 158 K. Sheet toughness can be increased more by using a lubricant-modified polystyrene grade with relatively high molecular weight such as PS 165 H, giving the relative values shown in the diagram of Figure 7 for the example of a sheet made from Styrolux 684 D and GPPS blended in a ratio of 4:6. The toughness and transparency properties of the sheet here generally vary in opposite directions, so although sheet produced using PS 165 H is tougher at the same blending ratio a slight loss of transparency has to be accepted.

4 Optical Properties Excellent transparency is one of the key properties of Styrolux products. High gloss, comparable with that of GPPS, is also a feature of Styrolux SBC. Two physical variables describe transparency: light transmission and haze. Transmission measures the intensity of light passing through a test specimen after taking into account reflection losses at the two surfaces. Haze is the proportion of light scattered by more than 2.5 from the incident direction on passage through a test specimen. Transmission and Haze Styrolux Grades All Styrolux grades have very good light transmission of about 9% in the visible region (4-8 nm - Table 3). Haze rises slightly as the toughness of the products increases. Guideline Values Transmission (%) Haze (%) Refractive Index n D C D G GPPS Table 3: Transmission, haze, and refractive indices of Styrolux to ASTM D13; measured on plaques of thickness 2 mm. Blends Made from Styrolux and GPPS The transparency of blends made from Styrolux and GPPS depends on the Styrolux grade (see Table 3), the blending ratio, the GPPS grade, and the homogeneity of the blend. Blending Ratio The content of the two components has a particular effect on sheet transparency. The approximately parabolic function (Figure 8) has a minimum where the Styrolux/GPPS blending ratio is about 4:6. Other blends have increasing transparency. The relative position of the transmission values is determined by the GPPS grades used. Haze values likewise follow an approximately parabolic curve with increasing content of Styrolux, this time with a maximum at a 4:6 Styrolux/GPPS blend. GPPS Grades Oil-free GPPS grades such as PS 158 K give the best transparency in blends with Styrolux SBC. Although toughness increases with oil-containing grades such as PS 143 E at the same blending ratio, transparency reduces. Blends made from Styrolux and PS 145 D give the best balance between high toughness and very good transparency. PS 145 D gives higher flowability than PS 158 K and PS 143 E. For identical blending ratios the sequence of increasing transparency within the BASF product line is: PS 165 H < 143 E < 145 D 158 K Homogeneity Inhomogeneity reduces the transparency of Styrolux/ GPPS blends. Good mixing performance by the extruder is an important precondition for the production of high quality sheet and high-transparency injection moldings without flow streaks.

5 Tensile stress [MPa] GPPS Styrolux 656 C Styrolux 3G 55 Penetration energy [Nm] PS 158 K PS 143 E 1 2 Tensile strain [%] GPPS content in Styrolux 684 D [%] Figure 1: Stress-strain curves for Styrolux 656 C, Styrolux 3G 55, and GPPS measured by the ISO 527 tensile test. Figure 5: Penetration energy as a function of GPPS content to ISO 663-2; measured on 1 mm sheet. Modulus of elasticity [MPa] D 3G GPPS content in Styrolux [%] Figure 2: Stiffness of Styrolux/GPPS blends; modulus of elasticity measured to ISO 527. Figure 6: For comparable toughness: reduction in Styrolux content by up to 25% using Styrolux 3G 55 (size of circles = measure of toughness). Tensile strain at break [%] Transverse Parallel Tensile strain at break [%] PS 158 K content in Styrolux 3G 55 [%] 158 K 145 D 143 E 165 H Figure 3: Tensile strain at break as a function of GPPS content (PS 158 K) in Styrolux 3G 55; measured on 1 mm sheet to ISO 527. Figure 7: Influence of polystyrene grade on toughness of sheet made from Styrolux 684 D and GPPS (blending ratio 4:6); measured to ISO 527. Force [N] HIPS Styrolux 684 D Transmission [%] PS 158 K PS 145 D PS 143 E Displacement [mm] Share of Styrolux [%] Figure 4: ISO penetration test on disks (diameter 5 mm, thickness 1 mm) for Styrolux 684 D compared with high-impact polystyrene. Figure 8: Transmission of Styrolux as a function of GPPS content and of GPPS grades; measured on sheet of thickness 1 mm to ASTM D13.

6 Styrolux SBC Styrolux is BASF s trademark for a portfolio of clear styrene-butadiene copolymers that offer a unique combination of outstanding clarity, exceptional toughness and low density resulting in a high-performance material that offers a significant yield advantage over many other clear materials. Designed with versatility and processability in mind, Styrolux SBC may be the right material to help make your products better. For more information about Styrolux SBC, please contact us at styrolux@basf.com. About BASF BASF: The Chemical Company. We don t make a lot of the products you buy. We make a lot of the products you buy better. BASF Corporation, headquartered in New Jersey, is the North American affiliate of BASF AG, Ludwigshafen, Germany. Rated in FORTUNE magazine as America s Most Admired Chemical Company, we employ about 1, people in North America. BASF is the world s leading chemical company: The Chemical Company. Our portfolio ranges from chemicals, plastics, performance products, agricultural products and fine chemicals to crude oil and natural gas. As a reliable partner to virtually all industries, BASF s intelligent solutions and high-value products help customers to be more successful. BASF develops new technologies and uses them to open up additional market opportunities. We combine economic success with environmental protection and social responsibility, thus contributing to a better future. Further information on BASF is available on the Internet at While the descriptions, designs, data and information contained herein are presented in good faith and believed to be accurate, it is provided for your guidance only. Because many factors may affect processing or application/use, we recommend that you make tests to determine the suitability of a product for your particular purpose prior to use. NO WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE MADE REGARDING PRODUCTS DESCRIBED OR DESIGNS, DATA OR INFORMATION SET FORTH, OR THAT THE PRODUCTS, DESIGNS, DATA OR INFORMATION MAY BE USED WITHOUT INFRINGING THE INTELLECTUAL PROPERTY RIGHTS OF OTHERS. IN NO CASE SHALL THE DESCRIPTIONS, INFORMATION, DATA OR DESIGNS PROVIDED BE CONSIDERED A PART OF OUR TERMS AND CONDITIONS OF SALE. All trademarks are owned by BASF AG or BASF Corporation. 26 BASF Corporation BASF Corporation 1 Campus Drive Florham Park, NJ 7932 Visit us online at