Bapolene MDPE 6316 is a medium-density polyethylene resin supplied by Bamberger Polymers, Inc. under the Bapolene trade name. The grade is defined by a nominal density of 0.936 g/cm³ and a nominal melt flow rate of 16 g/10 min at 190 °C/2.16 kg when tested to ASTM D1238. In the medium-density polyethylene class, the density remains below the 0.940 g/cm³ upper boundary, while the melt flow rate is positioned at the upper end of commercial MDPE injection-moulding ranges. The material is therefore directed toward thin-wall closures, overcaps, tubs, housewares, and small containers where mould-filling pressure, cycle time, and impact resistance are balanced against maximum load-bearing stiffness rather than optimized for stiffness alone. Typical mechanical values published for the grade include tensile yield strength of approximately 16 MPa, elongation at break above 500%, and 1% secant flexural modulus near 550 MPa. Tensile yield is measured on ASTM D638 Type IV specimens at 50 mm/min; flexural modulus is reported under ASTM D790. These values reflect the characteristic crystallinity of medium-density polyethylene: lower than HDPE homopolymer and higher than butene-based LLDPE. The resulting fracture and rigidity profile differs from both material classes, which is relevant when a processor considers substituting MDPE 6316 into an existing HDPE or LLDPE tool. The product should not be treated as a direct replacement for high-flow LDPE or LLDPE goods. Because the density is higher than that of typical LLDPE injection grades, parts exhibit greater modulus and lower elongation at yield. Compared with lower-flow MDPE grades used in rotational moulding, the higher melt flow rate reduces injection pressure and improves thin-wall fill, but it also reduces parison/melt strength and can increase susceptibility to drool in open-nozzle injection systems. Published data for this specific grade’s molecular weight distribution are limited; selection should be based on the supplier’s certificate of analysis and application-specific lot testing rather than generic MDPE data.

How Does a 16 g/10 min MDPE Behave in High-Cavitation Injection Moulding?

In high-cavitation injection moulding, the grade is processed on general-purpose single-stage screws with 20:1 L/D to 24:1 L/D and compression ratios from 2.0:1 to 2.8:1. Barrel temperatures typically follow a rising profile from 160 °C in the feed zone to 200–220 °C in the metering zone, with nozzle temperature maintained at 205–225 °C. The supplier’s published processing window for injection moulding commonly lists melt temperatures of 177–232 °C and mould temperatures of 10–32 °C. Chilled water at 10–15 °C is normally used to stabilize part dimensions and reduce post-mould shrinkage. Because the melt flow rate is 16 g/10 min, injection pressure drop through narrow gates is lower than for fractional-melt or 4–8 g/10 min MDPE. This enables thin-wall sections below 1.5 mm to be filled without excessive clamp force. However, the short gate freeze time associated with high-flow polyethylene demands precise switchover from velocity control to pressure control. Switchover should be set before the gate solidifies; otherwise cavity packing is lost and sink marks appear opposite the gate. A worn non-return valve is particularly damaging with this grade because screw recovery can outpace plastication, producing shot-to-shot cushion variation and short shot or flash defects. Hot-runner tools present a specific failure mode: the high-flow melt can drool from open nozzles when back pressure is below 0.5 MPa or when the shut-off nozzle is worn. A reverse-taper nozzle or spring-loaded shut-off nozzle is recommended. In hot-runner systems, the runner manifold should be held at the nozzle set point, and the hot sprue should not exceed 230 °C, because prolonged residency above that temperature can initiate oxidative chain scission detectable by a viscosity shift in subsequent ASTM D1238 measurements. Published residence-time stability data for this specific grade are limited, so processors must verify melt flow rate after purging and before restarting production. Polyethylene is not hygroscopic, so drying is not a chemical requirement. Surface moisture from cold-warehouse storage or condensation at relative humidity above 60% can be removed by purging with ambient air or by using a desiccant hopper dryer at 70 °C for 2 h. This is a handling control, not a devolatilization step.

If the Application Requires a Step-Change in Environmental Stress Crack Resistance

Compared with a typical 0.953 g/cm³ HDPE injection grade of similar melt flow, Bapolene MDPE 6316 is expected to show lower flexural modulus and longer failure time in ASTM D1693 environmental stress-crack resistance testing. The lower density reduces crystalline fraction, which lowers stiffness but improves resistance to slow crack growth under contact with surfactants, household cleaners, and certain mineral oils. This is the principal technical justification for selecting MDPE over HDPE in caps, overcaps, and containers exposed to stress-cracking agents. Published product-specific F50 data for MDPE 6316 may not be available in every supplier data sheet. When a closure or container is exposed to aggressive stress-cracking agents, a lot-specific ASTM D1693 Condition B test is recommended rather than relying on generic MDPE performance. The test should be run on compression-moulded plaques and, where possible, on injection-moulded parts because orientation and residual stress alter stress-cracking response. For parts with inconsistent wall thickness, sharp corners, or high gate-region residual stress, stress-cracking failure can initiate even when the material itself meets a given ESCR rating. In blow moulding, MDPE 6316 differs from HDPE by lower parison melt strength. The lower density reduces sag resistance at large shot sizes, so tooling designed for HDPE may require parison program adjustment or lower melt temperature to prevent wall thinning. For injection blow moulding of small containers, the higher flow assists core pin filling, but the core rod temperature must be controlled to avoid non-uniform crystal orientation that can produce sidewall splitting under top-load or drop impact. When the part is exposed to organic solvents rather than aqueous stress-cracking agents, the use of MDPE 6316 is outside its intended compatibility range. Strong oxidizing acids, chlorinated solvents, and aromatic hydrocarbons can swell or degrade the surface. For such environments, a fluoropolymer, polypropylene, or other chemical-resistant resin should be evaluated.

Melt Rheology, Shrinkage Control, and Regulatory Certification Data

Melt rheology at processing temperature follows shear-thinning behaviour typical of linear polyethylene with a medium molecular weight. The high melt flow rate indicates a relatively low viscosity at low shear; however the grade retains enough melt strength for thin-wall injection if gate and runner geometry are not excessively restrictive. No published capillary rheometry data for this specific grade are available in the standard datasheet; processors requiring injection simulation input should request shear-viscosity data from the supplier or generate a pressure-volume-temperature model from ISO 17744 or equivalent capillary measurements. Shrinkage behaviour is anisotropic and depends on wall thickness, mould temperature, and packing pressure. Typical mould shrinkage for injection-moulded MDPE 6316 is in the range of 0.018–0.022 mm/mm under ASTM D955, though higher values may occur in thick sections. To reduce warpage, gates should be located to create radial or uniform flow and avoid flow-length imbalances above 15% across the cavity. Post-mould shrinkage of MDPE can continue for 24–48 h; dimensional inspection should be delayed accordingly.

Typical physical properties reported for Bapolene MDPE 6316

Property	Test standard	Nominal value
Melt flow rate	ASTM D1238 / ISO 1133-1	16 g/10 min
Density	ASTM D1505	0.936 g/cm³
Tensile strength at yield	ASTM D638, Type IV, 50 mm/min	16 MPa
Elongation at break	ASTM D638	greater than 500%
Flexural modulus, 1% secant	ASTM D790	550 MPa
Vicat softening temperature	ASTM D1525	118 °C
Mould shrinkage	ASTM D955	0.018–0.022 mm/mm

The table values are nominal and are not intended as release limits. Lot-to-lot variance in density and melt flow rate should be controlled by the supplier’s certificate of analysis. Incoming inspection should include melt flow rate to ASTM D1238 and density to ASTM D1505 on each lot if the material is used in regulated packaging. Regulatory compliance must be confirmed by Bamberger Polymers’ current product stewardship letter. Polyethylene grades of this type may comply with FDA 21 CFR 177.1520 for olefin polymers when the density and extraction limits are met. However, the specific end-use condition of use under 21 CFR 176.170 or 21 CFR 177.1520(c) determines whether the material is suitable for food-contact packaging. REACH and RoHS compliance for heavy metals and restricted substances should be verified with the supplier; no statement of compliance is valid without the grade-specific lot data and the regulatory version in force at the time of supply.

Comparative position of MDPE 6316 versus generic injection-moulding polyethylenes

Attribute	Bapolene MDPE 6316	Typical HDPE injection grade	Typical butene LLDPE injection grade
Density	0.936 g/cm³	0.950–0.960 g/cm³	0.918–0.925 g/cm³
Melt flow rate	16 g/10 min	4–20 g/10 min	20–50 g/10 min
Flexural modulus	550 MPa	900–1200 MPa	250–350 MPa
Environmental stress crack resistance	Improved versus HDPE	Lower	High
Typical injection melt temperature	177–232 °C	190–240 °C	170–200 °C

The comparative values are generic class data from open polymer databases and are not supplier lot specifications for Bapolene MDPE 6316. They illustrate the selection logic: MDPE 6316 offers a midpoint in stiffness between LLDPE and HDPE while retaining the processability of a high-flow injection grade. In injection moulding trials, the material should be purged with a clean polyethylene before shutdown. Because the grade contains antioxidant stabilizers, purging with PVC or acetal is not recommended; decomposition products from those resins can contaminate the feed throat and produce black specks. Avoid combination with amine-based additive masterbatches unless the specific additive system has been verified, because certain hindered amine light stabilizers can interact with phenolic antioxidants under high-temperature processing and shift colour or long-term heat-aging performance. For colour compounding, let-down ratios should follow the masterbatch supplier’s recommendation, typically 2–4% for polyethylene carrier systems. High-shear dispersion is not required for pigment distribution at this melt flow rate, but poor dry blending can produce colour swirl in thin-wall parts. A gravimetric blender with accuracy of ±0.1% on the colour feed is recommended when running naturally pigmented resin. Bapolene MDPE 6316 is not a drop-in replacement for HDPE in applications requiring high top-load strength, high heat deflection temperature, or tight dimensional stability at elevated temperatures. The Vicat softening temperature of approximately 118 °C limits use in hot-fill containers above 70 °C unless sidewall reinforcement or vacuum panel design compensates for thermal softening. Published data for this specific configuration under hot-fill conditions are limited.