NOVA Chemicals HDPE 2607-UV9 is a high-density polyethylene rotational molding resin supplied with the UV9 stabilization package. The product is identified by a nominal melt index of 5.0 g/10 min determined at 190°C under 2.16 kg according to ASTM D1238 and a nominal solid density of 0.945 g/cm³ according to ASTM D1505. These values place the grade in the intermediate-flow range for rotational molding HDPE, where melt index provides sufficient flow for rib fill and insert encapsulation while retaining molecular weight for environmental stress cracking resistance. The UV9 package differentiates the material from unmodified HDPE 2607 and from general-purpose rotomolding HDPE that relies on carbon black addition or post-molding painting for outdoor durability. The values shown in this technical introduction are nominal and do not replace a certificate of analysis.

Typical Property Set and Test Method Cross-Reference

These values represent representative supplier data for the product class and should be verified lot by lot. Lot-to-lot variation in melt index and density is controlled by the manufacturer’s release limits; however, the exact release window is determined by the supply agreement and may vary with production campaign.

How Does 2607-UV9 Compare with General-Purpose Rotomolding HDPE?

Compared with an unmodified 0.945 g/cm³ rotomolding HDPE of the same melt index class, the short-term mechanical behavior of 2607-UV9 is similar. Tensile yield strength falls in the 23–25 MPa range, elongation at break is above 500%, and flexural modulus occupies the 900–1100 MPa range. The distinction appears in long-term outdoor service and in environmental stress cracking resistance. ESCR testing according to ASTM D1693 Condition A, F50 is reported above 1000 h for 2607-UV9, while high-flow rotomolding grades with melt index above 8.0 g/10 min frequently fall below 500 h. This difference is relevant for chemical tanks and outdoor enclosures where hoop stress and detergent contact coexist.

Unlike crosslinked HDPE, 2607-UV9 is a non-crosslinked thermoplastic and cannot maintain equivalent creep resistance under continuous stress above 60°C. It can be reground and re-used more readily than crosslinked material, but it should not be substituted for peroxide- or silane-crosslinked HDPE in hot-chemical or high-temperature applications. Compared with a higher-density 0.955 g/cm³ HDPE, 2607-UV9 provides better low-temperature ductility and ESCR but lower modulus and load-bearing stiffness.

UV Stabilization and Weatherability Test Protocols

Accelerated weatherability of 2607-UV9 is assessed by xenon arc exposure according to ISO 4892-2 and by fluorescent UV exposure according to ASTM G154. The UV9 package is designed to preserve tensile elongation and surface appearance in colored outdoor parts, but it is not equivalent to a carbon black package for opacity or for surface temperature behavior under solar load. Weathering acceptance criteria for UV-stabilized HDPE parts often require retention of at least 70% of original tensile elongation after 3000 h xenon arc exposure, but published data for this specific configuration is limited. The supplier’s accelerated weathering data should be obtained for the intended pigment loading and part wall thickness. In high-UV arid climates, thin sections below 3.2 mm may develop surface microcracking earlier than thicker sections because the stabilizer reservoir is limited and the exposed surface consumes stabilizer over time.

On a carousel rotational molding machine using a forced-convection oven set point of 285–315°C, a 4:1 rotation ratio, and a 4.8 mm nominal wall thickness, 2607-UV9 typically reaches a peak internal air temperature of 190–210°C after 10–14 min of mold dwell. The mold surface temperature may run 20–40°C higher than the internal air sensor. The 5.0 g/10 min melt index supports densification at the lower end of the HDPE processing window, but incomplete coalescence appears as pinholes and microporosity on the inner surface behind deep ribs, molded-in inserts, and parting-line offsets. A water mist cooling step during the cooling segment, applied after the internal air temperature falls below 90°C, reduces warpage in flat panels. Rapid forced-air cooling below 60°C can introduce residual stress and later dimensional movement, particularly in parts with wall thickness variation greater than 3.2 mm. For cylindrical parts on rock-and-roll equipment, the intermediate melt index may require a lower oven set point or shorter dwell than a 3.0 g/10 min low-flow grade; the uniaxial rotation rate should be tuned to avoid polymer degradation at the upper surface of the mold.

When the Part Requires Low-Temperature Impact Resistance

Low-temperature impact behavior is a primary selection criterion for playground equipment, agricultural tanks, and outdoor enclosures. The density of 0.945 g/cm³ places 2607-UV9 in the intermediate-density HDPE range, where low-temperature ductility is better than 0.955–0.960 g/cm³ HDPE and stiffness is higher than 0.938 g/cm³ medium-density polyethylene. Instrumented drop weight testing according to ASTM D5276 and the Association of Rotational Molders low-temperature impact method are used to compare parts at -40°C. Published data for this specific configuration is limited; however, the 5.0 g/10 min melt index and the high ESCR indicate higher retained molecular weight than typical high-flow rotomolding grades, which contributes to low-temperature puncture resistance. The trade-off is that a 0.955 g/cm³ grade provides higher flexural modulus and better creep resistance in warm, load-bearing service, while a 0.938 g/cm³ medium-density grade may offer even greater low-temperature impact at the cost of stiffness and chemical permeability.

Continuous-Load and Elevated-Temperature Boundaries

HDPE 2607-UV9 remains thermoplastic and creep-susceptible under sustained load. Creep modulus for 0.945 g/cm³ HDPE at 23°C can fall to 30–50% of the short-term flexural modulus within 1000 h depending on applied stress; long-term design should follow ISO 899-1 or ASTM D2990 using the actual service temperature. Heat deflection temperature at 0.455 MPa according to ASTM D648 for this density class is typically in the 55–75°C range, and continuous load-bearing service above 40°C is not recommended without creep-rupture testing. Thermal expansion coefficients for HDPE according to ASTM D696 or ISO 11359-2 are in the 100–200 μm/m·°C range; a 1.0 m panel cycled between -30°C and 40°C can undergo dimensional changes of 7–14 mm. Mounting flanges must accommodate this movement rather than rigidly restraining the part.

Effect of Powder Particle Size Distribution on Densification

The pulverized powder used for rotational molding of 2607-UV9 must be controlled for particle size distribution. HDPE rotational molding powders are typically classified to 35 mesh (500 μm) with a controlled fraction passing 200 mesh (75 μm). A distribution skewed toward coarse particles slows heat transfer, delays bubble removal, and produces outer-surface pinholes; an excess of fines reduces bulk density and can accumulate in mold parting lines. Bulk density measured according to ASTM D1895 Method A for pulverized HDPE is typically in the 0.35–0.45 g/cm³ range, and dry-flow measurements according to ASTM D1895 Method B are used to detect powder morphology changes. The intermediate melt index of 5.0 g/10 min reduces sensitivity to particle size compared with 3.0 g/10 min low-flow grades, but the processor should verify that the powder has not been exposed to excessive moisture. Pre-drying is generally not required if the powder is stored in sealed containers below 60% relative humidity; open storage can introduce sufficient surface moisture to generate steam porosity during heating.

Pigmentation and mineral fillers can alter the weathering behavior of UV9. High loadings of titanium dioxide may improve opacity but can interact with stabilizer packages and shift color drift under xenon arc exposure; the supplier’s pigment compatibility matrix should be consulted. Recycled or post-industrial content above 10% can dilute the UV9 package and reduce ESCR below the values published for virgin material. When regrind is used, it should be blended with documented upper limits and the final part should be re-qualified for impact and weatherability.

Selecting 2607-UV9 for Outdoor Chemical Storage

Chemical storage parts made from 2607-UV9 are governed by environmental stress cracking rather than simple dissolution. ESCR testing according to ASTM D1693 uses 100% Igepal CO-630 at 50°C; values above 1000 h under Condition A indicate suitability for continuous contact with aqueous detergents, mild acids, and alkalis at ambient temperature. The resin is not recommended for concentrated oxidizing acids such as nitric acid, or for aromatic and chlorinated solvents that plasticize the amorphous polyethylene phase. Hydrocarbon storage above 40°C accelerates creep and reduces long-term ESCR. Molded-in brass or stainless steel inserts create local stress concentrations; flange and corner radii should be kept above 6.4 mm to avoid crack initiation. Aggressive chemical applications should be validated by immersion testing according to ASTM D543 under the actual service temperature and stress state.

Regulatory status for 2607-UV9 must be verified for the exact formulation and end-use exposure. In the United States, olefin polymers intended for food contact may be assessed under 21 CFR 177.1520, which includes specifications for high-density polyethylene and limits for extractable fractions. The UV stabilizer package must have separate clearance. REACH registration and RoHS Directive 2011/65/EU restrict homogeneous material concentrations of lead to 0.1%, cadmium to 0.01%, mercury to 0.1%, and hexavalent chromium to 0.1%. The unpigmented polymer does not intentionally introduce these metals, but recycled or post-industrial content can alter trace composition. A certificate of compliance for the specific part geometry and service condition is required before commercial use.