What Happens to Notched Izod and Vicat Softening When SEBS Enters a Polypropylene Homopolymer Matrix?

In injection-moulded polypropylene homopolymer formulations, Kraton G1640 E is introduced at 10–20 phr to shift the ductile-brittle transition downward and reduce stress whitening caused by craze nucleation at impact. On a 40:1 L/D co-rotating twin-screw line with barrel set-points from 200 °C to 230 °C and a screw speed of 280 min⁻¹, the SEBS phase is dispersed into domain sizes below 1.5 µm; this dispersion is retained when injection moulding uses melt temperatures of 215–235 °C and mould temperatures of 40–60 °C. Notched Izod values measured according to ASTM D256 Method A at −30 °C climb from 2.0 kJ/m² for the neat matrix to 8.5–12 kJ/m² at the 15–20 phr addition window, while flexural modulus according to ISO 178 decreases from 1,450 MPa to approximately 820 MPa; the trade-off is non-linear and becomes steep above 25 phr. Vicat B120 softening temperature measured under ISO 306 falls from 104 °C to 86–89 °C in the same loading range, restricting automotive interior compounds to applications below 85 °C continuous heat. Pre-drying of pelletized compound at 80 °C for 2 h is required when storage relative humidity exceeds 60%; otherwise surface water evolves at the vent port and produces silver streaks at injection gate areas. The compound should not be combined with amine-based antistatic additives above 0.3 wt% because discolouration accelerates at melt temperatures above 235 °C.

For peristaltic pump tubing extruded on a 24:1 L/D single-screw line with five-zone barrel profiles from 175 °C to 210 °C, G1640 E serves as the principal elastomeric component at 35–45 wt% of the compound. A typical bench formulation contains 40 wt% G1640 E, 45 phr USP-grade white mineral oil, 8 phr polypropylene homopolymer, 2 phr high-density polyethylene, and 0.15 phr hindered phenolic antioxidant; hardness lands at 35 Shore A by ASTM D2240, and tensile strength measured at 500 mm/min under ISO 37 remains at 4.2 MPa with elongation above 500%. The compound is evaluated for cytotoxicity according to ISO 10993-5, for acute systemic toxicity and intracutaneous reactivity under USP Class VI, and for extractables according to USP <661.1>; because G1640 E is fully hydrogenated, the formulation avoids the aromatic residue profile typical of SBS or SIS medical elastomers. Sterilization validation commonly runs an ethylene oxide cycle at 55 °C and 65% RH; gamma sterilization at 25 kGy produces yellowness index shifts below 2 units under ASTM E313, but doses above 35 kGy begin to increase crosslinking and reduce ultimate elongation by more than 15%. Operators observe torque values below 55% of motor rating when the screw speed is kept at 60 min⁻¹; if screw cooling is not engaged at 65 °C, melt-block ring forms at the feed section because the low-midblock glass transition region densifies under compression. Pre-drying at 75 °C for 2 h is mandatory when packing hall relative humidity exceeds 60%; surface moisture produces visible bubble defects in tube walls after 20 min of continuous extrusion. The material is not recommended for continuous contact with strong oxidizing disinfectants or with lipid-rich emulsions above 50 °C because oil extraction shifts the Shore A hardness upward and reduces pump-resilience fatigue life.

When G1640 E Replaces SIS in High-Temperature Hot-Melt PSA Carriers

When G1640 E replaces SIS in hot-melt pressure-sensitive adhesive formulations for masking tape and durable label constructions, the saturated midblock does not generate the thermo-oxidative viscosity drift observed with unsaturated styrene-isoprene-styrene carriers during sustained holding at 170 °C for 8 h. A production batch in a jacketed sigma-blade mixer with nitrogen blanket incorporates 100 phr G1640 E, 120 phr fully hydrogenated hydrocarbon tackifier, 60 phr white mineral oil, and 0.5 phr secondary antioxidant; final Brookfield viscosity at 175 °C falls between 8,000 mPa·s and 14,000 mPa·s depending on tackifier softening point. Loop tack measured according to ASTM D6195 reaches 12–18 N/25 mm on stainless steel, while shear adhesion failure temperature under ASTM D4498 is 85–95 °C; equivalent SIS carriers in the same tackifier system typically fail below 75 °C. Coating at 150–165 °C on a slot-die line requires the adhesive to maintain viscosity below 20,000 mPa·s; when tackifier loading exceeds 150 phr, the mix becomes stringy and build-up on the doctor roll increases. The formulation is not suited for freezer-label tack at temperatures below −20 °C unless a low-Tg aliphatic tackifier is combined with a low molecular weight diblock compatibilizer; pure triblock G1640 E systems exhibit low wet-out on low-energy polyolefin films if corona treatment is below 38 mN/m.

On rotary two-shot machines with 150 t clamp force, insert injection moulding of PC/ABS hard substrates overmoulded with a 35 Shore A G1640 E compound requires barrel temperatures not exceeding 235 °C to avoid degradation of the hard-substrate surface and melt-pressure fluctuation from high viscosity. The soft-touch component is moulded at 200–220 °C with mould surface temperature maintained at 45 °C; bond strength at the interface measured by peel testing under ISO 4578 remains above 2.5 N/mm when the hard substrate is preheated to 65 °C before insert placement. Abrasion resistance of the soft-touch layer evaluated by ASTM D4060 with CS-17 wheels and 1,000 g load shows volume loss below 90 mm³ after 500 cycles, while gloss at 60° under ASTM D523 remains below 8 GU in high-talc compounds to avoid fingerprint smear. Gate blush is observed when injection speed exceeds 45 mm/s; the compound’s low melt-flow rate under ISO 1133-1 necessitates a wide gate land and vent depth of 0.02 mm. Pre-drying at 80 °C for 2 h is required if the material has been stored at ambient humidity above 60%. The system is not recommended for uninterrupted service in contact with artificial sebum or sunscreen-based esters above 50 °C, because cyclic siloxane and ester migration can reduce interfacial peel strength by more than 20% in 72 h.

Halogen-Free Sheathing Compounds Where ATH and MDH Loadings Exceed 60 wt%

In halogen-free flame-retardant cable sheathing compounds, G1640 E is used to preserve elongation and low-temperature flexibility when aluminium trihydrate and magnesium dihydroxide loadings reach 60–70 wt%. The compound is manufactured on a 44:1 L/D co-rotating twin-screw extruder with side-feeder injection of fillers after polymer melting; barrel set-points are held at 155–175 °C because ATH begins releasing water above 190 °C and MDH above 330 °C, but localized shear heating in the side-feeder zone can exceed 200 °C at screw speeds above 250 min⁻¹. A typical formulation contains 22 wt% G1640 E, 10 wt% EVA with vinyl acetate content 28%, 5 wt% polyethylene, 60 wt% ATH, 8 wt% zinc borate, and 1.5 wt% processing oil; tensile strength under ASTM D638 Type V remains above 8 MPa and elongation above 180%. Limiting oxygen index measured according to ASTM D2863 is typically 34–36%, and pilot-burner flame spread under IEC 60332-1-2 passes when sheath wall thickness is above 0.5 mm. The processing boundary is narrow: at filler loadings above 70 wt%, die pressure rises beyond 22 MPa and the extrudate surface transitions from smooth to sharkskin unless an aqueous cooling bath at 40 °C is used immediately after the die. Zinc borate addition above 8 wt% increases Shore D hardness by more than 5 points and reduces elongation more than 25%. The compound should not be processed with amine-functional coupling agents because moisture release from filler surfaces triggers ammonia evolution and voids in the sheath at the crosshead.

Cast film lines processing 55 wt% calcium carbonate-filled G1640 E for breathable hygiene backsheet require feed-zone barrel cooling to 150 °C and downstream zones at 210–230 °C to prevent the mineral filler from nucleating premature moisture vaporization at the feed throat. The compound is formulated with 100 phr G1640 E, 65 phr naphthenic oil, 120 phr calcium carbonate with mean particle size 1.5–2.0 µm, and 0.3 phr fluoropolymer processing aid; the film is cast at 25 µm thickness and stretched in the machine direction at a ratio of 2.5:1 and transverse direction at 1.7:1 on an intermeshing roll orientation unit. Water vapour transmission rate measured by ASTM E96/E96M at 38 °C and 90% RH lands between 1,800 g/m²/day and 2,800 g/m²/day, while hydrohead according to ASTM D751 remains above 600 mm H₂O; the pore distribution is bimodal when stretching is performed below 70 °C, producing pin holes and lowering hydrohead below 300 mm H₂O. Edge tears in the orientation unit occur when calcium carbonate dispersion quality drops below a Hegman gauge reading of 5, so twin-screw compounding must achieve melt temperature below 205 °C and screw speed above 300 min⁻¹ for adequate distributive mixing. The saturated SEBS midblock resists oxidative degradation during cast film trim reuse up to 20 wt% regrind; higher regrind fractions increase gel counts and generate specks visible under ASTM D1003 haze testing.

Run Compression-Moulded Foam at 35 Shore A Without Melt-Strength Collapse

During compression moulding of footwear midsoles, G1640 E compounds with 45–55 wt% polymer are blended with 50–80 phr naphthenic oil, 10–20 phr polypropylene homopolymer, and 5 phr microcellular blowing agent masterbatch. Moulding at 150–170 °C for 8–12 min produces densities of 0.28–0.42 g/cm³, hardness of 25–35 Shore A under ASTM D2240, and rebound resilience above 45% under ASTM D7121. Compression set measured after 22 h at 70 °C according to ASTM D395 Method B remains below 35% because the saturated midblock resists chain scission during repeated heat exposure. Ross flex crack initiation under ASTM D1052 exceeds 150,000 cycles without visible cut growth at −10 °C. A production limitation arises when blowing agent decomposition is not synchronized with the low melt strength of G1640 E; if mould pressure is released before 4 min, cells collapse near the mould skin and form a non-uniform foam core. Pre-drying compound blanks at 70 °C for 2 h is necessary when the mixing room relative humidity exceeds 60%, otherwise pinholing appears at the flash line.

Phthalate-free toy compounds governed by Directive 2009/48/EC use G1640 E to eliminate phthalate migration risk, but melt strength limits high-speed spiral pin extrusion of thin-walled toy parts below 1.5 mm wall thickness. The compound contains 30–40 wt% G1640 E, 45–55 phr white mineral oil, 10–20 phr polypropylene, and 0.3–0.8 wt% slip agent; hardness is adjusted to 25–30 Shore A for squeeze toys and 50–60 Shore A for building blocks by varying polypropylene content. Migration of specific elements is tested under EN 71-3 and volatile organic compounds under ISO 16000-6; the saturated styrene-ethylene/butylene backbone limits benzene and 1,3-butadiene residuals to below typical detection limits. In injection moulding with a 160 t clamp force line, gate freeze time is longer than flexible PVC; holding pressure must be maintained for 8–12 s per 1 mm wall thickness to avoid sink marks at rib intersections. Pre-drying at 75 °C for 2 h is required at storage humidity above 60%. The compound is not recommended for repeated exposure to isopropyl alcohol or ethanol-containing cleaning solutions above 30 °C; oil extraction causes surface tack and gloss changes under ASTM D523.