Kraton Kraton™MD SEBS MD6945
- Product Name: Kraton Kraton™MD SEBS MD6945
- Factroy Site: Yinchuan, Ningxia, China
- Price Inquiry: sales8@ascent-chem.com
- Manufacturer: Ascent Petrochem Holdings Co., Limited
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- Kraton Kraton™MD SEBS MD6945 is typically used in formulations when hardness and melt-flow rate must be controlled within specific ranges.
| HS Code | 669830 |
| Product Name | Kraton™ MD6945 |
| Polymer Type | SEBS (styrene-ethylene/butylene-styrene) block copolymer |
| Molecular Structure | Linear triblock copolymer |
| Styrene Content | 20 wt% |
| Physical Form | Dusted pellets |
| Color | White to off-white |
| Specific Gravity | 0.91 |
| Density | 0.91 g/cm³ |
| Bulk Density | Approximately 0.5 g/cm³ |
| Shore A Hardness | 45 |
| Melt Flow Rate | Approximately 5 g/10 min at 230°C/2.16 kg |
| Tensile Strength | Approximately 30 MPa |
| Elongation At Break | Approximately 500% |
| 300 Modulus | Approximately 3.5 MPa |
As an accredited Kraton Kraton™MD SEBS MD6945 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Kraton MD6945 SEBS supplied in 25 kg moisture-resistant paper bags, palletized for industrial handling and storage. |
| Container Loading (20′ FCL) | Kraton MD6945 SEBS is palletized and loaded into a 20-foot FCL container, secured and documented for compliant ocean shipment. |
| Shipping | Shipping description for Kraton™ MD SEBS MD6945: solid SEBS polymer pellets supplied in moisture-resistant bags or octabins on pallets. Not classified as dangerous goods (UN not applicable). Keep dry, cool, and out of direct sunlight; avoid heat, moisture, and packaging damage during transport and storage. |
| Storage | Store in a cool, dry, well-ventilated area away from direct sunlight, heat, sparks, and open flames. Keep containers tightly closed to prevent moisture, dust, and contamination. Protect from strong oxidizers and avoid prolonged high temperatures. Use first-in, first-out stock rotation; no special storage conditions are generally required for this SEBS polymer. |
| Shelf Life | Kraton™ MD SEBS MD6945 has a recommended shelf life of 24 months when stored in original, unopened packaging under dry, ambient conditions. |
Medical fluid transfer tubing based on Kraton™ MD6945, a clear high-flow hydrogenated styrenic block copolymer with supplier-published nominal Shore A hardness of 35 and melt flow rate of 22 g/10 min at 230°C/5 kg by ASTM D1238, is first compounded on a co-rotating twin-screw extruder with an L/D ratio of 40:1, screw speed 350–500 rpm, and barrel temperatures from 160°C to 200°C. The compound formulation typically contains 100 phr MD6945, 10–30 phr polypropylene homopolymer, 10–25 phr medicinal-grade white mineral oil, and 0.05–0.3 phr hindered phenolic antioxidant. Barium sulfate is side-fed at 10–30 wt% when radiopacity is required; this increases melt pressure by 10–18% on a 25 mm twin-screw extruder at 400 rpm and reduces extrudate swell, so the die land length is extended by 15–20% to recover dimensional stability. Melt filtration through 200–250 mesh breaker plates is used to remove gel particles, and die pressure fluctuation is maintained below ±0.5 MPa to limit wall thickness variation. The pelletised compound is then extruded through a single-screw tubing line fitted with a barrier screw, L/D 25:1–30:1, compression ratio 2.5:1–3.0:1, and die melt temperature 190–215°C. The tube enters a water bath held at 15–25°C and is pulled at 25–60 m/min to maintain a wall thickness tolerance of ±0.03 mm. The main production-line failure mode is shark skin at melt temperature below 185°C, which is corrected by raising the die zone temperature without allowing the melt to exceed 215°C. Peristaltic pump segments are annealed at 70°C for 2 h to reduce residual orientation and improve cyclic fatigue life. Gamma irradiation at 25–50 kGy is preferred for sterilisation; electron beam above 75 kGy can induce gel formation in the ethylene/butylene midblock, visible as surface pitting and an increase in gel index. The terminal article is a translucent, plasticiser-free catheter or peristaltic pump shunt with Shore A hardness 35–50 by ASTM D2240, tensile strength above 12 MPa by ISO 37, elongation at break above 400%, and tear resistance above 30 kN/m. Oil addition above 25 phr is not recommended for connector bonding because migration can reduce adhesion to polycarbonate luer fittings and create a hazy surface after terminal sterilisation.
| Standard | Condition or method | Acceptance criterion |
|---|---|---|
| ISO 10993-5:2009 | MEM elution extraction, 24 h at 37°C, L-929 cells | Cytotoxicity grade ≤ 2 |
| USP <88> Class VI | Extraction at 121°C saline, 70°C alcohol, 50°C PEG 400 | Intracutaneous and systemic pass |
| FDA 21 CFR 177.1810 | Final article compositional check | Subject to end-use limitations in paragraph (c) |
| ISO 10555-1:2013 | Intravascular catheter shaft burst and leakage | No leak at rated pressure |
| REACH (EC) No 1907/2006 | SVHC screening | Candidate list substance < 0.1 wt% |
| RoHS Directive 2011/65/EU | Pb, Hg, Cd, Cr(VI), PBB, PBDE | MCV limits per Annex II |
What Limits Two-Shot Overmolding Adhesion to Semi-Crystalline Polypropylene?
On two-shot injection moulding cells with clamp force from 800 kN to 2,500 kN, Kraton™ MD6945 is injected as the soft component at 190–230°C onto a polypropylene substrate. The bond mechanism depends on interdiffusion of the ethylene/butylene midblock into the PP skin at temperatures above 130°C. If the mould temperature is maintained below 30°C, the PP surface remains quenched and the failure mode in T-peel testing changes from cohesive rubber tearing to adhesive delamination; peel strength measured by ISO 11339 is typically 2–4 N/mm instead of 8–12 N/mm for a cohesive bond. The soft compound is prepared from MD6945 60–80 phr, polypropylene homopolymer 10–25 phr, white mineral oil 0–20 phr, and optional mineral filler 0–10 phr. Oil addition above 20 phr creates a migratory boundary layer that can reduce peel force by 30% or more after 7 days at 50°C. Mould temperature is raised to 35–50°C, injection speed set to 80–150 mm/s, holding pressure to 40–70 MPa, and cooling time to 10–20 s. If the PP substrate has been stored at more than 60% relative humidity, it is dried before overmoulding because steam bubbles at the interface cause localised adhesive voids. Barrel residence time should not exceed 6 min at 230°C because chain scission in the styrene end-blocks lowers Shore A hardness and increases surface tack. The terminal product is a soft-touch surgical instrument handle or blood glucose meter housing grip. For medical enclosures, the overmoulded part is assessed by ISO 10993-5:2009 and ISO 10993-10:2010 skin-contact extraction. For consumer electronics and food-contact closure applications, the selected compound is verified against FDA 21 CFR 177.1810 or the relevant EU food-contact measure.
Impact Modification of Homopolymer Polypropylene for Semi-Structural Appliance Housings
Twin-screw compounding of MD6945 into homopolymer PP is carried out at 190–220°C on a co-rotating extruder with L/D 40:1, screw speed 600–900 rpm, and underwater pelletising controlled at 30–40°C to prevent pellet agglomeration. Elastomer content of 5–25 wt% is dispersed as discrete domains of 0.5–2.0 μm, confirmed by TEM or AFM; domains below 0.5 μm increase melt viscosity but produce less impact improvement unless a maleic anhydride-grafted PP compatibiliser is used. The compound is injection moulded into appliance housings at 200–230°C, mould temperature 30–50°C, clamp tonnage 1,200–3,000 kN, and back pressure 3–6 MPa. Notched Charpy impact at -20°C measured by ISO 179-1:2010 type 1A typically remains below 4 kJ/m² when MD6945 is ≤ 10 wt%; at 20 wt% it can exceed 10 kJ/m² in homopolymer PP, while tensile modulus measured by ISO 527-2:2012 falls from 1,500 MPa to below 900 MPa. The ductile-brittle transition is steep, so addition levels between 12 wt% and 18 wt% require lot-specific verification rather than use of a nominal design value. High-density polyethylene is added at 5–15 wt% to restore melt flow and reduce die drool. Pre-drying at 65°C for 2 h is required when silo or open-floor storage exceeds 60% relative humidity. Strongly basic additives are avoided in these compounds when acidic filler systems are present because salt formation can raise melt viscosity and cause pellet surface roughness. The terminal product is a vacuum cleaner housing, appliance panel, or small enclosure requiring semi-structural stiffness; final parts are evaluated for notched impact, tensile yield, and Vicat softening per ISO 306.
Elastic film laminates for wound-care and hygiene are produced by dry blending Kraton™ MD6945 with high-flow polypropylene at 20–40 wt% and extruding on a 90 mm cast film line at 180–210°C, line speed 80–150 m/min, die gap 0.8 mm, and chill roll temperature 15–20°C. Film thickness of 50–120 μm is qualified for elastic recovery after 300% strain per ASTM D5459; MD6945 content above 25 wt% is required to maintain recovery above 90%, and corona treatment to 38 mN/m is used before lamination to nonwoven. ISO 10993-5:2009 and ISO 10993-10:2010 apply for wound-contact use.
When Flame-Retardant Mineral Filler Alters Screw Torque in SEBS-Based Jacketing
Flexible jacketing for appliance wire is compounded from Kraton™ MD6945 40–60 phr, paraffinic process oil 20–40 phr, calcium carbonate 10–30 phr, and metal-hydrate flame retardant 5–15 phr. The compound is mixed on a two-roll mill or co-rotating twin-screw at 170–190°C, then extruded onto tinned copper conductors through a crosshead die with pressure screw L/D 20:1–24:1. The addition of aluminium trihydrate above 15 phr can increase specific energy input by 10–18% and release combined water if the melt exceeds 190°C; therefore the die temperature is held at 175–185°C and screw cooling is applied in the feed zone. Pre-compounded pellets are dried at 60°C for 2 h before extrusion to avoid surface porosity. The insulation passes IEC 60332-1-2 flammability when wall thickness is at least 0.8 mm, and a 2 mm plaque achieves UL 94 V-0. Hardness is 55–75 Shore A by ASTM D2240, tensile strength above 8 MPa by ISO 37, elongation at break above 300%, and volume resistivity above 1×10¹² Ω·cm by IEC 62631-3-1. The terminal product is a flexible appliance cord jacketing or internal wiring insulation requiring RoHS and REACH declarations. Lead-based stabilisers and cadmium pigments are excluded; the compound must also be checked against the SVHC candidate list under REACH. If a brominated flame retardant is used as a secondary FR, its selection must not conflict with UL 94 after heat ageing at 100°C for 168 h.
Respiratory mask cushions and soft seals are produced by injection moulding a compound of Kraton™ MD6945 55–75 phr, high-flow polypropylene 10–20 phr, white mineral oil 10–25 phr, and slip agent 0.1–0.3 phr. The mould surface is textured to reduce gloss; clamp force ranges from 1,000 kN to 2,500 kN, injection temperature is 190–225°C, holding pressure 50–80 MPa, and cooling time 15–25 s. Mould gas vents 0.02–0.03 mm deep are used to prevent burn marks at the flow front. Compression set is evaluated per ISO 815-1:2019 after 22 h at 70°C under 25% strain; values remain below 35% when oil content is below 20 phr but rise above 45% when oil exceeds 25 phr. Hysteresis at 50% elongation is below 18% when measured by cyclic tensile test. The finished cushion is assembled onto polycarbonate frames; the SEBS compound must contain no migratory amides above 0.1%, because residue in ISO 10993-10 smear tests may produce an irritant response. Compatibilisation is not required if PP is below 20 phr, but higher PP levels produce visible flow lines and an unacceptable stiffening of the seal edge. The terminal product is a reusable CPAP mask cushion that is washed at 70°C and must retain dimensional tolerance for 90 days of cyclic use. Published data for this exact fatigue configuration is limited; seal life claims should be verified on the final assembly using the manufacturer's expected cleaning protocol.
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- Kraton Kraton™MD SEBS MD6945 is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
- COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales8@ascent-chem.com.
Kraton™ MD6945 is a linear styrene-ethylene/butylene-styrene block copolymer supplied as an oil-free, high-molecular-weight base polymer for thermoplastic compounding, extrusion, and injection molding. The saturated ethylene/butylene midblock is obtained by hydrogenation of butadiene repeat units, which removes most residual olefinic unsaturation and provides a measurable improvement in oxidative stability over unsaturated styrene-butadiene-styrene block copolymers during high-shear melt processing and elevated-temperature end use. The grade is not an oil-extended compound; it is supplied neat, leaving formulators control over process oil type, filler loading, stabilizer package, and final hardness. Nominal bound styrene content is commonly reported at 13 wt%, placing the product in the low-styrene SEBS class rather than the 28–32 wt% high-styrene products used for harder, higher-tensile compounds. Raw-polymer density is typically 0.90–0.91 g/cm³ when measured according to ISO 1183-1:2019. Melt mass-flow rate is usually determined at 230 °C under a 5 kg load per ISO 1133-1:2022 and is generally in the low single-digit range for this molecular weight class. The certificate of analysis for the specific lot remains the controlling acceptance document.
What Distinguishes Kraton™ MD6945 from High-Styrene SEBS Grades?
The principal structural difference is the ratio of polystyrene end blocks to the saturated ethylene/butylene midblock. High-styrene SEBS products with 28–32 wt% bound styrene form a larger volume fraction of glassy styrene domains at ambient temperature. The result is a stiffer, stronger elastomer with a more pronounced yield point and a higher upper service temperature. The low-styrene architecture of the MD6945 class reduces the number of styrene load-bearing domains and shifts the mechanical response toward a lower-modulus rubber plateau. Tensile curves are typically long and flat; stress at break is lower, but elongation at break increases when compared against high-styrene grades of similar molecular weight. This trade-off is the central formulation decision when selecting MD6945 for oil-free soft-touch or low-hardness compounds.
| Comparative parameter | Low-styrene, high-molecular-weight SEBS class | General-purpose SEBS class | High-styrene SEBS class |
|---|---|---|---|
| Bound styrene content, wt% | 12–15 | 20–25 | 28–32 |
| Raw polymer density, g/cm³ per ISO 1183-1:2019 | 0.90–0.91 | 0.91–0.92 | 0.92–0.95 |
| Typical melt mass-flow rate at 230 °C/5 kg, g/10 min | 1–10 | 5–25 | 3–20 |
| Hardness response in oil-free compounds | Low Shore A; extended elastomer plateau | Mid-range Shore A | Higher Shore A or Shore D; increased tensile strength |
| Primary formulation consequence | Higher oil uptake before softening; lower modulus at fixed oil loading | Balanced oil uptake and tensile strength | Higher strength and elevated styrene glass transition; reduced oil tolerance |
Table 1 is a structural comparison of commercial SEBS families, not a lot-release specification. The values are typical product-class windows and must be confirmed against the supplier certificate of analysis.
Another formulation difference is oil level. Oil-extended SEBS pellets arrive with 50–150 phr of paraffinic oil already mixed; this fixes the softness and reduces the formulator’s ability to use the same polymer for low-extractables or medical applications. Because MD6945 is supplied neat, it can be oil-extended during compounding at the exact level required, or used without oil for applications in which plasticizer migration is unacceptable. This difference is often monitored by extraction testing per ISO 6427:2013 and by total volatile organic condensate testing in automotive customer specifications. The oil-free form also simplifies regulatory assessment when the polymer is used in food-contact articles because there is no legacy oil component to characterise.
Morphologically, the product derives its elastomeric recovery from physical crosslinks, not covalent vulcanization. The polystyrene end blocks aggregate into glassy domains that are stable below the glass transition of the styrene phase, but dissolve into the melt above that transition, allowing reprocessing. Unlike sulfur-vulcanizable diene elastomers, SEBS has no significant residual unsaturation in the rubber midblock; therefore sulfur cure is not applicable and peroxide cure is generally inefficient. The elastic plateau is controlled by the size and spacing of the styrene domains and by midblock entanglement. In oil-loaded compounds, paraffinic or naphthenic process oil partitions into the ethylene/butylene phase. Aromatic oil is normally avoided because it can plasticize the styrene domains and lower the upper use temperature. Once the oil concentration exceeds the midblock absorption limit, macroscopic surface bloom occurs. The threshold is formulation-dependent but is commonly observed in the 70–150 phr range for low-styrene SEBS compounds containing paraffinic process oil; published data for this specific configuration is limited.
Bulk Melt Rheology and Twin-Screw Compounding Thresholds
The melt is strongly shear thinning. Capillary rheometry at 200–230 °C typically shows power-law index values below 0.5 at apparent shear rates of 100 s−1–1,000 s−1 for high-molecular-weight SEBS melts. The practical consequence is that increasing screw speed raises output with a diminishing torque rise, but also raises viscous dissipation near the screw tips and mixing blocks. On a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1, a typical barrel profile maintains the feeding zone at 40–60 °C, melting at 180–200 °C, and die temperature at 210–230 °C. Vacuum venting in the penultimate barrel is standard practice; when vacuum is lost, moisture-induced porosity can appear in pellets or molded articles even though the polymer itself is not hygroscopic. Pre-drying at 70–80 °C for 2–4 h is recommended when storage relative humidity exceeds 60%.
When process oil is required, downstream injection after the melt seal is preferred over feed-throat addition. Total oil addition at the feed throat can create a lubricated feed zone that suppresses frictional melting and shifts the first mixing section from dispersive to distributive action. A split injection at the sixth and eighth barrels on a 40:1 machine is one production configuration that limits wall slip while preserving filler dispersion. Because the melt is viscous, torque and die melt temperature must be monitored; sustained excursions above 250 °C for more than 5 min can produce yellowing, gel-particle formation, and measurable tensile-strength loss. In oil-compounding, the hardness curve is nonlinear. At low oil addition, hardness decreases approximately linearly, but above a formulation-specific threshold, further oil addition reduces tensile strength sharply while hardness changes little. This cliff edge frequently occurs between 60 phr and 120 phr of paraffinic oil for low-styrene SEBS; the exact location depends on oil flash point, kinematic viscosity at 100 °C, and mixing intensity. The curve should be mapped experimentally for the specific supplier lot because average molecular weight and styrene domain spacing shift the threshold.
In soft-touch overmolding onto a rigid polypropylene substrate, injection molding machines with clamp forces from 800 kN to 2,500 kN and barrel profiles of 190–220 °C are common production platforms. Mold temperatures are kept between 20 °C and 40 °C to maintain cycle time. The bond to polypropylene is formed by melt interdiffusion rather than by a separate adhesive, but adhesion can be increased by plasma or corona treatment of the substrate before overmolding. Compound hardness is typically adjusted to Shore A 25–55 as measured per ISO 7619-1:2010. Adhesion measured by T-peel testing per ASTM D1876 varies strongly with substrate grade, surface treatment, and part geometry; published multi-lot data for this specific grade is limited.
When Oil-Free Softness Without Plasticizer Migration Is Required in Medical or Consumer Contact
MD6945 is used in formulations for grips, diagnostic-instrument housings, syringe plunger tips, and respiratory-mask cushioning when the article requires low Shore A hardness without the persistent migration of low-molecular-weight process oil. The saturated midblock resists autoxidation more effectively than SBS in oxygen-rich or steam-sterilized environments, but stabilizer choice and final article validation remain mandatory. Cytotoxicity evaluation is conducted according to ISO 10993-5:2009; sensitization and irritation are evaluated per ISO 10993-10:2010 for applications in which skin contact is continuous or repeated. Food-contact suitability may be assessed under 21 CFR 177.1810 in the United States and under Regulation (EU) No 10/2011 in the European Union. These standards do not provide automatic clearance; the final compound must be tested because fillers, oils, stabilizers, and colorants change migration behavior.
| Assessment area | Standard or regulation | Typical application in MD6945 compound evaluation |
|---|---|---|
| Density | ISO 1183-1:2019 | Raw polymer and compound density for mass conversion and void detection |
| Melt mass-flow rate | ISO 1133-1:2022 | Batch-to-batch melt viscosity screening at 230 °C/5 kg |
| Tensile stress-strain | ISO 37:2017 or ASTM D638-14 | Molded sheets or plaques; modulus, tensile strength, and elongation at break |
| Hardness | ISO 7619-1:2010 or ASTM D2240 | Shore A hardness of final compounds after oil and filler incorporation |
| Food-contact suitability | 21 CFR 177.1810; Regulation (EU) No 10/2011 | Regulatory evaluation of formulated article, migration testing |
| Hazardous substances | Directive 2011/65/EU as amended; Annex II | RoHS heavy-metal and phthalate screening of final compound |
| REACH | Regulation (EC) No 1907/2006 | SVHC screening and authorization list review |
| Medical biocompatibility | ISO 10993-5:2009; ISO 10993-10:2010 | Cytotoxicity, sensitization, and irritation for limited-contact devices |
The base polymer is only one element of the regulatory file. RoHS screening of the formulated compound is conducted under Directive 2011/65/EU as amended, and REACH SVHC screening follows Regulation (EC) No 1907/2006. Heavy-metal and phthalate content in final parts may depend more on the pigment, filler, and carrier resin than on the SEBS itself. If the article is subjected to repeated steam sterilization at 121 °C or to gamma irradiation above 25 kGy, post-exposure tensile and compression-set testing is required to confirm that the saturated midblock has not been compromised by residual oil oxidation or stabilizer depletion. Compression set is controlled by styrene content, oil level, and processing history. Low-styrene SEBS compounds tend to have higher compression set than high-styrene or covalently crosslinked thermoplastic vulcanizates; if compression set at 70 °C per ISO 815-1:2019 below 35% is required, oil-free MD6945 compounds may need annealing or a radiation-crosslinked network. Published data for this specific grade in oil-free formulations is limited.
In polymer modification, low-styrene SEBS is used as an impact modifier in polypropylene and polyethylene compounds at loadings commonly below 20 wt%. The rubber domains increase resistance to crack initiation, while the low bound-styrene content limits the increase in modulus and melt viscosity compared with a high-styrene SEBS used at similar loading. Notched Izod impact strength per ISO 180/A and tensile modulus per ISO 527-2:2012 are standard evaluation methods for such compounds. In bituminous roofing and pavement modification, high-molecular-weight SEBS is processed in high-shear mixers at temperatures below the thermal degradation threshold; published data for this specific grade in asphalt formulations is limited, and plant-scale stability must be established with the specific bitumen source, filler package, and mixing equipment.
