Kraton™ D1193 P is a clear, linear styrene-butadiene-styrene thermoplastic elastomer supplied as a free-flowing powder. The polymer is defined by a polystyrene endblock content of 30 mass % in a linear A-B-A architecture, in which the styrene domains phase-separate below approximately 95 °C and function as physical crosslinks without vulcanization. The continuous butadiene phase provides elastomeric extension and recovery between approximately -80 °C and 70 °C. Because the midblock retains unsaturation, the grade is differentiated from hydrogenated styrenic block copolymers such as SEBS and SEPS; the unsaturation permits post-polymerization modification and free-radical grafting but simultaneously lowers oxidative resistance. The manufacturer’s product specification identifies a specific gravity of 0.94 g/cm³ and total volatile matter not exceeding 0.5 mass %. The “P” designation refers to the powder presentation, which enables direct dry blending with fillers, resins, and bitumen in low-shear mixers rather than requiring the pre-melting step common to porous-pellet grades.

In hot-melt adhesive and sealant compounding, D1193 P is typically processed in jacketed sigma-blade or planetary mixers at melt temperatures from 160 °C to 180 °C, with a nitrogen sweep to limit oxidative gel formation. The powder wets into hydrocarbon resin and process oil systems more rapidly than pellet forms, but the dry particles tend to absorb atmospheric moisture. When the powder is conveyed from outdoor silos or stored in open bulk bags at relative humidity above 60 %, pre-drying at 55 °C to 65 °C for 2 h to 4 h is required before extrusion; failure to do so can produce surface defects, reduced melt strength, and vacuum-vent foaming.

Warehouse storage of D1193 P should maintain product temperature below 30 °C and protect the bags from direct sunlight. The powder can acquire static charge during pneumatic conveying; all transfer lines should be grounded, and inert gas blanketing is recommended when the powder is conveyed into areas where solvent vapours are present. SBS powder is not classified as a dangerous good under the UN Model Regulations for transport, but dust accumulation should be controlled to avoid secondary dust explosion hazards. Bulk density variation between lots affects volumetric feeder calibration; loss-in-weight feeders with refill-tolerant control algorithms reduce short-term feed drift on high-speed extrusion lines.

What separates D1193 P from saturated and higher-styrene block copolymers?

The primary differentiation is architectural and compositional. Kraton™ D1193 P is a linear SBS with 30 mass % polystyrene; it does not contain the radial coupling points found in some higher-molecular-weight SBS grades, and it is not hydrogenated. Relative to Kraton D1101, a linear SBS with approximately 31 mass % styrene and a high melt viscosity, D1193 P is designed for lower melt viscosity and higher throughput in hot-melt and melt-compounding equipment. Relative to higher-styrene SBS grades, the lower aromatic phase fraction reduces melt stiffness and increases elastomeric character, but it also reduces tensile strength and solvent resistance. In comparison with SEBS grades such as Kraton G1650, the unsaturated polybutadiene midblock of D1193 P provides better compatibility with aliphatic tackifying resins and bitumen, yet requires phenolic or phosphite antioxidants during high-temperature compounding because the polybutadiene backbone is susceptible to autoxidation.

In pressure-sensitive and hot-melt adhesive systems, D1193 P is typically formulated with C5 aliphatic tackifying resins and naphthenic white oils. The formulation window is limited by oil bleed-out above approximately 30 mass % oil, depending on resin aromaticity; the low polystyrene content of 30 mass % provides a balance between tack and cohesive strength. Hot-melt viscosity is measured with a Brookfield RVDV or equivalent at 177 °C with spindle 27; changes in viscosity after 24 h at 177 °C are used as a quality indicator for thermal stability. Because the butadiene midblock is unsaturated, addition of 0.3 mass % to 0.5 mass % hindered phenolic antioxidant is standard in hot-melt formulations to suppress gel particle formation.

For polymer-modified bitumen, D1193 P is incorporated at 3 mass % to 7 mass % in high-shear mills at 170 °C to 190 °C. The powder dissolves faster than pelletized SBS under the same mixing energy, but absorbed moisture must be removed before mixing to prevent foaming in the binder. The resulting binder is evaluated by softening point (ASTM D36-06), penetration (ASTM D5-06), and elastic recovery (ASTM D6084-04). The unsaturated SBS improves low-temperature cracking resistance and high-temperature rutting resistance relative to straight-run bitumen, but storage stability requires low-shear agitation to prevent phase separation.

Rheological and tensile characterisation for melt-processed formulations

Melt flow is evaluated according to ASTM D1238-20 or ISO 1133-1:2022 at 200 °C with a 5 kg load. D1193 P exhibits an order of magnitude higher melt-flow index than high-molecular-weight linear SBS grades; the exact value must be taken from the manufacturer’s certificate of analysis, because melt-flow index alone does not fully describe the shear-thinning behavior of SBS triblock melts. Rotational rheometry with 25 mm parallel plates at 1 Hz shows a pronounced loss factor increase above 120 °C as the polystyrene domains soften. Tensile properties are measured on compression-moulded sheets according to ASTM D638-14 at 23 °C and 50 mm/min; published data for this specific configuration is limited, and end-users should request grade-specific tensile sheets rather than relying on generic SBS property tables. Shore A hardness is determined according to ASTM D2240-15e1, and solvent resistance is evaluated by mass uptake in ASTM D471-16 oils and solvents.

When pre-drying is bypassed on humid twin-screw extrusion lines

On a twin-screw extruder with L/D 40 or greater, D1193 P powder is commonly fed through a side stuffer into a melt stream of polypropylene or bitumen. If the powder has equilibrated at RH 60 % or higher, water vapor released in the compression zone can disrupt polymer wetting and generate microscopic voids. The standard corrective setup is a desiccant dryer delivering air at a dew point of -40 °C and a drying hopper temperature of 55 °C to 65 °C. Over-drying above 70 °C is not recommended because free-flowing powder can agglomerate into lumps that bridge the feed throat. Vacuum vent pressure is typically maintained below -0.08 MPa for devolatilization of residual moisture and low-molecular-weight oligomers. Processing operators report that inadequate pre-drying produces batch-to-batch variability in melt pressure and torque rather than a single reproducible failure mode, which complicates troubleshooting on production lines.

In polypropylene modification, D1193 P is compounded at 190 °C to 210 °C with a twin-screw extruder configured with distributive mixing elements and an upstream atmospheric vent. The SBS phase improves impact toughness, but the improvement is strongly dependent on the dispersed rubber particle size achieved during mixing. At screw speeds above 500 rpm on a 40 mm co-rotating extruder, shear heating can exceed 230 °C locally and initiate butadiene degradation, observed as an increase in melt-flow index and a shift in color. Addition of 0.1 mass % to 0.3 mass % phenolic antioxidant and 0.1 mass % phosphite stabilizer is typical for protecting the unsaturated midblock during compounding. Avoid compounding with strong acids or chlorinated solvents, which promote acid-catalyzed depolymerization or swelling of the polybutadiene phase.

The powder presentation has a higher surface-area-to-volume ratio than porous pellets, which accelerates dissolution in hot-melt mixers and bitumen mills. This benefit is partially offset by higher moisture uptake under ambient storage and a greater tendency to bridge in hoppers with shallow cone angles. In production-scale operations, the use of vibratory bin activators and cone angles greater than 60° prevents flow stoppage. Sieve analysis according to ASTM D1921-18 is used to verify particle-size distribution, but published typical distributions are limited; therefore, incoming inspection should compare each lot against the supplier’s certificate of analysis rather than a fixed generic specification.

Oxidative ageing thresholds emerge above 70 °C in continuous air exposure

The polybutadiene midblock in D1193 P is more sensitive to thermal-oxidative ageing than hydrogenated SEBS or SEPS midblocks. Continuous exposure in air above 70 °C can produce chain scission and crosslinking simultaneously, shifting hardness, tensile elongation, and melt-flow index. Accelerated ageing is evaluated according to ISO 188:2023 or ASTM D573-04(2023) in forced-air ovens at 70 °C or 100 °C. The presence of phenolic antioxidant packages retards carbonyl formation, but unsaturated midblocks should not be specified for continuous service in contact with copper naphthenate or cobalt-based oxidation catalysts, which accelerate polybutadiene autoxidation. For outdoor exposure, UV stabilization is required; unstabilized SBS undergoes surface crazing and loss of elongation in accelerated QUV testing under ASTM G154-23 cycle conditions.

In direct comparative trials on 25 mm co-rotating twin-screw extruders, D1193 P reaches equivalent dispersion quality in polypropylene at lower screw speed than D1101, but impact-modifier efficiency is sensitive to particle-size distribution. The lower melt viscosity of D1193 P allows compounding temperatures to be reduced by 10 °C to 15 °C relative to high-molecular-weight SBS grades, which lowers thermal degradation risk. Published data for this specific configuration is limited, so these observations should be verified on the target line before changing from an existing SBS grade.

Regulatory compliance for D1193 P is application-dependent. The polymer is subject to REACH registration under Regulation (EC) No 1907/2006, and it is generally free of the restricted substances listed in Annex II of Directive 2011/65/EU (RoHS). Food-contact use requires verification against the appropriate national and regional positive lists; for styrene block copolymers, FDA 21 CFR 177.1810 is often referenced, but migration testing under EN 1186-1:2002 remains necessary for finished articles. The following checklist identifies the core standards applicable to industrial specification and quality control.