DSM HDPE SB117 appears in legacy material specifications as an unreinforced high-density polyethylene grade directed toward sheet extrusion, thermoforming, and rigid packaging applications. The SB117 designation is product-specific but is not consistently described in current open-access datasheets; after polyolefin asset transfers, current lot-level technical data from the successor supplier must be treated as controlling. This discussion distinguishes SB117 from other HDPE products through processing behaviour, standard test methods, and application boundaries. Where certified SB117 values are unavailable, the text states that published data for this specific configuration is limited and provides general class-level reference points from polyolefin extrusion practice.

Viscosity, density and melt-flow classification of SB117

Melt-mass flow rate under ISO 1133-1:2022 at 190 °C and 2.16 kg is the primary sorting parameter. An extrusion-stable HDPE of this class is commonly specified below 0.8 g/10 min, with many lot releases falling between 0.2 g/10 min and 0.6 g/10 min. Density measured by gradient column or immersion according to ISO 1183-1:2019 typically lies between 0.945 g/cm³ and 0.962 g/cm³; values outside this band usually indicate either a different comonomer level or contamination from incompatible regrind.

Tensile yield stress determined under ISO 527-2:2012 or ASTM D638-14 generally sits between 22 MPa and 30 MPa for the density class, while flexural modulus under ISO 178:2019 or ASTM D790-17 is commonly 1050 MPa to 1400 MPa. Charpy notched impact strength under ISO 179-1:2010 at 23 °C may exceed 10 kJ/m², but sub-zero behaviour is less forgiving: at -30 °C values below 5 kJ/m² are possible. Tensile elongation at break under ISO 527-2 is typically above 600 % for uncontaminated HDPE; a sharp decline below 200 % usually indicates contamination from incompatible polymers or severe oxidative degradation. These figures are class-level reference points, not certified SB117 release limits.

Weight-average molecular weight and molecular weight distribution are not commonly printed on HDPE datasheets. Instead, rheological indicators such as melt-flow ratio and extensional viscosity are used. The ratio of high-load to standard-load melt-flow rates determined under ISO 1133-1:2022 at 21.6 kg and 2.16 kg provides a rough indication of molecular weight distribution; for SB117-class extrusion HDPE, this ratio is typically between 15 and 30. Narrow-distribution grades flow more uniformly through sheet dies but may display lower sag resistance.

Rheologically, a melt in this flow range can be represented by the Carreau-Yasuda model. Zero-shear viscosity at 190 °C is typically between 5 kPa·s and 25 kPa·s; product-specific shear-thinning index and the transition shear rate must be obtained by capillary rheometry under ISO 11443. Melt strength measured with a capillary break-off or Rheotens attachment often lies between 0.08 N and 0.20 N at standard acceleration, while bimodal high-molecular-weight HDPE can exceed 0.35 N. This difference has direct consequences for sag control during thermoforming and is not visible in the standard melt-flow-rate value.

Drying of SB117 is not normally required when internal moisture is below 0.10 % by mass. On production lines with outdoor silo storage or regrind incorporation above 15 wt%, moisture pick-up at relative humidity above 60 % can produce surface splay and pinholes at the die lip. A desiccant hopper-dryer set to 80 °C for 2 h to 4 h is a conservative countermeasure only when condensation is observed; prolonged high-temperature drying can oxidise granule surfaces and shift yellowness index under ASTM D1925.

Extrusion of SB117 on a 75 mm single-screw extruder with 30:1 L/D and a barrier screw generally begins with barrel set points from 180 °C at the feed zone to 220 °C at the metering zone. Head and die temperatures are usually held at 210 °C to 225 °C. The melt temperature measured by an insertion probe should not remain above 240 °C for prolonged periods; oxidative gel formation and yellowing can occur. Screen-pack sequences of 20/40/60/100 mesh provide gel filtration, and a pressure rise above 180 bar across the pack typically indicates screen replacement. A melt pump between extruder and die reduces pressure pulsation and improves sheet caliper consistency, but it does not correct melt-temperature non-uniformity.

Sheet thickness variation is governed by die-lip adjustment, melt-temperature uniformity, and roll-gap force. A melt pump with pressure transducers mounted upstream and downstream allows a closed-loop pressure differential of ±0.5 bar. If the differential exceeds this value because of screen fouling, machine-direction thickness variation may exceed ±0.02 mm, which becomes visible as downstream thermoforming webbing.

What limits the thermoforming window for high-density polyethylene sheet?

The practical sheet-forming window is controlled by the interval between the crystalline melting point and surface-oxidation onset. By differential scanning calorimetry under ISO 11357-3:2018, HDPE in the SB117 density class typically shows a peak melting temperature near 130 °C to 135 °C. Sheet surface temperature must exceed this by only a narrow margin to avoid frozen-in orientation; plug-assisted forming of shallow-draft trays commonly uses a sheet surface temperature of 165 °C to 185 °C.

When the sheet is unsupported by mechanical frames, the upper acceptable surface temperature can be as tight as ±5 °C. At sheet thicknesses below 1.0 mm, the forming window narrows to approximately ±3 °C because radiative heat loss is rapid relative to sheet thermal mass. Ceramic-tube infrared ovens with top and bottom zones controlled to 5 °C resolution are therefore required for stable output on deep-draw tools.

On three-roll stack units, roll temperatures of 70 °C to 95 °C are used to control flatness and shrinkage. A middle roll temperature below 65 °C can cause premature release and curl. At line speeds above 6 m/min for 1.2 mm sheet, edge ripple and transverse caliper variation greater than ±0.03 mm measured with a scanning beta gauge can appear unless roll-gap closure force is matched to melt viscosity. These are production-scale failure modes observed on conventional three-roll sheet lines.

The cooling rate from melt to below crystallization onset determines crystallinity and shrinkage. At a roll-surface temperature of 85 °C, a 1.2 mm HDPE sheet may leave the stack at 95 °C to 105 °C. Stack cooling performance is therefore not only a throughput issue; residual heat raises subsequent thermoforming sag. Inadequate water flow through roll internals can produce a temperature differential between roll ends of 5 °C to 10 °C, which appears as variable cross-web shrinkage.

Additive bloom from slip or antistatic agents should not be confused with stress cracking. Migration kinetics in the semi-crystalline matrix are diffusion-limited; at service temperatures below 40 °C, a C18-amide slip additive can require days to weeks to bloom. If an amine-containing external antistatic coating is introduced, oxidative induction time under ISO 11357-6:2018 should be re-evaluated because some amine chemistries can interact with phenolic/phosphite stabiliser packages and reduce long-term thermal stability. This is not specific to SB117, but it is operationally relevant because unlubricated HDPE sheet can accumulate static charge during trimming and stacking.

Colour masterbatches with a polyethylene carrier are preferred for SB117. Organic pigment formulations often achieve satisfactory dispersion at let-down ratios of 2 % to 4 %, while inorganic pigments may require 6 % to 8 %. Screw mixing sections of 5D to 8D are usually sufficient at melt temperatures below 240 °C; higher temperatures can degrade the masterbatch carrier and produce visible streaks.

Regrind levels between 20 % and 40 % are routinely used for non-contact packaging sheet. Above 40 %, physical property loss in SB117-like grades is often modest, but gel count under ASTM D3351 can increase because repeated extrusion consumes the phenolic antioxidant. An oxidative induction time below 20 min at 210 °C under ISO 11357-6:2018 suggests stabiliser depletion and indicates that the regrind stream should be reduced or re-stabilized.

When hostile wetting agents drive environmental stress-crack resistance specifications

HDPE is vulnerable to environmental stress cracking when formed parts remain under residual stress in contact with polar organic compounds, surfactants, or automotive fluids. Bent-strip testing under ASTM D1693-21, condition B or C, in 10 % Igepal CO-630 solution at 50 °C is the most widely reported method. The notched constant tensile load test under ISO 16770:2019 provides a failure-time curve under fixed stress at 50 °C in 2 % Arkopal N100 solution and is more discriminating for slow crack growth. Published data for SB117 in this specific configuration is limited; lot-specific ESCR data must be requested when wetting-agent exposure is expected.

Resistance to slow crack growth is controlled by molecular weight distribution and comonomer placement, not by density alone. Bimodal high-molecular-weight HDPE grades often exceed 1000 h in condition B ESCR, whereas a unimodal sheet grade of identical density can fail before 100 h. This is a critical product difference: if SB117 is used as a drop-in replacement for a bimodal HMW-HDPE without verification, aggressive surfactant contact at a sharp corner can produce brittle fracture below the tensile yield point.

The temperature dependence of slow crack growth follows an Arrhenius relation for many HDPE grades, with an apparent activation energy of approximately 40 kJ/mol to 60 kJ/mol. At 23 °C, failure under 10 % Igepal solution can take months; at 50 °C, failure often occurs within days to weeks. Accelerated ESCR testing therefore provides ranking data but does not automatically predict room-temperature service life without a validated shift-factor model.

For thermoformed cups and trays with sharp radii, inside corner thickness should be maintained above 0.25 mm when wetting-agent contact is possible. Local strain concentration in the radius can exceed the bulk yield strain even when average part thickness appears adequate. Weld-line regions in sheet or fused structures can show tensile strength reductions of 20 % to 50 % relative to bulk values under ISO 527-2, which makes stress-crack initiation more probable at melt-boundary zones.

SB117 differs from LLDPE and HMW-HDPE in processing and forming behaviour. LLDPE has lower density and higher dart impact but lower flexural modulus; HMW-HDPE has higher melt strength and better ESCR but requires higher torque and head pressure. Medium-molecular-weight HDPE of the SB117 class offers lower screw motor load and easier melt conveying than HMW-HDPE of similar density, but its sag resistance during thermoforming is correspondingly lower. The table below lists class-level distinguishing profiles.

For coextrusion or extrusion-coating use, SB117 should not be selected without a melt-strength comparison against dedicated coating grades. In a typical coextrusion structure with a 0.35 mm HDPE cap layer and a 0.70 mm regrind core, edge instability at draw-down ratios above 15:1 can appear if the melt elasticity is insufficient. A chill-roll temperature of 45 °C to 60 °C and an air gap of 100 mm to 150 mm represent initial starting conditions; adjustment should use instrumented neck-in and basis-weight measurement rather than visual inspection alone.

In sound-deadening or packaging applications where SB117 sheet is adhesive-laminated to a foam core, corona surface energy above 42 mN/m is usually required for wetting of water-based adhesives. If surface energy decays below 38 mN/m within 24 h of treatment, the sheet may require inline plasma or corona immediately before lamination. This operational boundary arises from nonpolar surface chemistry and additive bloom; it does not imply an inherent defect in SB117 but must be included in process specifications.