Kraton™ D1157 is a linear styrene-butadiene-styrene triblock copolymer supplied as porous pellets with a silica partitioning agent for free-flowing storage. The manufacturer’s specification places bound styrene content at 29.5–31.5 mass%, with the butadiene midblock forming the remaining mass. The polymer is amorphous at service temperature and develops physical crosslinks through phase separation of glassy styrene domains; it contains no vulcanizing curatives and is processed by thermoplastic methods. Typical neat-polymer properties are nominal values and are not release specifications.

What separates D1157 from adjacent linear SBS grades in melt adhesive compounding?

Grade selection in the D-series linear SBS line is governed primarily by melt flow rate, styrene content, and diblock level. D1157 occupies an intermediate position between D1155 and D1159. The lower melt flow rate of D1155 increases melt residence time and shear heating but raises compounded hot melt viscosity and hot shear resistance. D1159 flows more readily and can wet low-energy surfaces more rapidly, but its lower molecular weight reduces cohesive strength. D1157 is therefore specified where a sprayable or extrusion-applied hot melt requires a balance between line speed, substrate penetration, and peel resistance.

The values in the table are nominal and may vary with production lot. Melt flow rate measured under ASTM D1238 at 200 °C/5 kg is a single-point quality control index; it does not fully describe shear-thinning behavior in a hot melt applicator operating between 100 s⁻¹ and 1,000 s⁻¹. Diblock content and styrene domain connectivity can shift the viscosity-shear rate curve even when melt flow rate remains within specification.

In production-scale hot melt adhesive compounding, D1157 is typically charged first into a jacketed sigma-blade mixer or a co-rotating twin-screw extruder with an L/D of 40:1 or greater. The processing window used in many facilities is 150 °C to 180 °C; above 200 °C, oxidative degradation of the butadiene midblock accelerates and can produce gel specks visible in a 0.2 mm slot-die film. Nitrogen blanketing or vacuum devolatilization is used when volatile content must be held below 1 mass%. The polymer is added with a primary phenolic antioxidant and, in high-temperature operations, a secondary phosphite stabilizer at 0.3–0.8 phr to reduce viscosity drift. The exact stabilizer loading depends on the tackifier and oil package and is confirmed by oven aging of the finished adhesive at 177 °C for 72 h with periodic melt viscosity measurement.

A generic hot melt assembly or packaging adhesive based on D1157 may contain 20–35 mass% polymer, 40–60 mass% C5/C9 aliphatic-aromatic tackifier resin, and 15–30 mass% naphthenic or paraffinic process oil. Addition sequence affects adhesive performance: charging tackifier before the polymer has completely fused can plasticize the styrene domains and reduce shear adhesion failure temperature. High-shear mixing in a twin-screw extruder at 160–170 °C produces finer styrene domain dispersion than low-shear sigma-blade mixing, but requires die pressure monitoring because improper screw configuration can generate localized temperatures above 200 °C at the melt seal.

D1157 exhibits a two-phase morphology after cooling. Differential scanning calorimetry under ASTM D3418 typically detects a butadiene-phase glass transition near -85 °C and a styrene-phase glass transition near 95 °C, though measured values depend on thermal history and heating rate. The styrene domains act as physical crosslinks and are responsible for the rubbery plateau in tensile stress-strain behavior. At styrene contents below 29 mass%, the domains become less continuous and cohesive strength drops; above 32 mass%, the compound stiffens and hot melt tack is reduced.

Peel adhesion of D1157-based hot melts is commonly evaluated by ASTM D903 for 180° peel or ASTM D1876 for T-peel, using 25.4 mm wide specimens and a peel rate of 300 mm/min. Shear adhesion failure temperature is measured by a dynamic method based on ASTM D4498 with a prescribed static load and temperature ramp; laboratories often use a 500 g load and a 22 °C/h ramp. The reported shear adhesion failure temperature for a given formulation depends on adhesive coat weight and substrate, so values cannot be compared across laboratories without identical specimen history.

Relative to ethylene-vinyl acetate copolymers used in hot melt packaging, D1157 offers lower melt density and a wider low-temperature flexibility window because the butadiene midblock remains elastomeric below -40 °C, whereas ethylene-vinyl acetate with 28 mass% vinyl acetate begins to stiffen near 0 °C. Compared with amorphous polyalphaolefin, D1157 exhibits higher tensile strength at the same coat weight and lower viscosity at comparable application temperature, but it is less resistant to prolonged ultraviolet exposure. Compared with SEBS, D1157 contains unsaturation in the butadiene midblock and therefore requires stronger antioxidant protection during high-temperature processing; SEBS is selected where outdoor weatherability and thermal oxidative resistance are dominant requirements.

Solvent-borne adhesive compounding imposes narrower viscosity limits than hot melt mixing

D1157 dissolves in toluene, cyclohexane, and blends of acetone with methyl ethyl ketone. The polymer is commonly handled at 20–35 mass% solids in contact adhesives and laminating adhesives. In good solvents, the butadiene midblock swells and solution viscosity rises rapidly as concentration approaches 35 mass%; rotogravure and comma-roll coaters therefore require solids reduction when Brookfield viscosity exceeds the coating head limit. Aromatic solvents solvate both blocks, while aliphatic solvents preferentially solvate the butadiene midblock and may leave styrene domains as swollen aggregates. This lowers solution clarity but does not necessarily reduce dried-film strength.

Solvent evaporation rate determines film formation temperature. Fast-evaporating solvent blends can trap a more disordered styrene domain network, shifting the stress-strain curve toward lower tensile strength and higher elongation. Dried films recover equilibrium morphology after annealing above the styrene glass transition temperature for several minutes. In production, contact adhesive solutions based on D1157 are often applied at dry coat weights between 0.05 mm and 0.2 mm, with open time controlled by solvent selection and substrate porosity. Published data for a given coating line is limited because solvent vapor concentration and air velocity alter the evaporation rate.

When D1157 Replaces Lower-Flow SBS in Sealant Formulations

Substitution of D1157 for D1155 in silicone-free construction sealants usually lowers mixing torque and permits higher throughput through profile extrusion equipment. The lower melt viscosity also allows lower processing temperatures. The principal trade-off is plasticizer retention: because D1157 has a lower molecular weight than D1155, process oil mobility increases and oil migration to unprimed glass or powder-coated metal can develop under sustained compression. Formulators compensate by reducing oil content by 3–5 phr or by raising the tackifier softening point. Tensile testing under ASTM D638 after aging at 70 °C for 168 h is one method to detect embrittlement or oil migration; the pass/fail limit depends on the construction specification, not on the polymer alone.

Extrusion rheometry at 180 °C can detect melt fracture when the die L/D is below 10:1. In sealant profiles, sharkskin is minimized by lowering extrusion speed or using a die with 15:1 L/D and a matte release coating. D1157 compounds with filler loadings above 20 mass% calcium carbonate may require a coupling agent to prevent filler dewetting; failure appears as rough surfaces and reduced elongation at break.

Compared with SIS triblock copolymers, D1157 has a higher midblock glass transition temperature and lower hot tack at comparable melt flow rate. It is therefore less common in low-temperature pressure-sensitive tapes but provides higher tensile strength and better shear holding power at ambient temperature in assembly adhesives. Published data for D1157 in removable pressure-sensitive adhesive configurations is limited because SIS and acrylic polymers dominate that segment. D1101, a higher-molecular-weight SBS grade, is more common in bitumen modification and highly cohesive sealants, while D1157 is easier to melt process and more compatible with high-resin adhesive formulations.

Compliance status under food-contact adhesive schemes

Neat Kraton™ D1157 is manufactured under REACH registration and appears on the TSCA inventory for the United States. The product is not a food-contact substance by itself; suitability for indirect food-contact adhesives depends on the fully formulated product and must be evaluated under 21 CFR 175.105 or equivalent national legislation. Formulators intending food-contact status must ensure that all tackifiers, oils, and antioxidants in the finished adhesive satisfy the same regulatory condition. For medical device assemblies, the finished product must be qualified under ISO 10993-1, including leachables and biocompatibility endpoints relevant to the device contact duration.

Storage in unopened bags at ambient temperature is typically specified for 24 months from the date of manufacture. Because the porous pellet surface can collect atmospheric moisture under relative humidity above 60%, bags should be closed immediately after use. If surface moisture is visible, conditioning at 60 °C for 1–2 h before melt processing is common; published data for this drying protocol across all climatic conditions is limited. The material contains butadiene unsaturation and is not suitable for continuous outdoor exposure without an effective ultraviolet stabilization package.