REPOL PP Homopolymer H200MA is a propylene homopolymer produced by Reliance Industries Limited and supplied in pellet form for injection-moulding applications. The grade carries a nominal melt mass-flow rate of 20 g/10 min when measured at 230 °C under a 2.16 kg load using ISO 1133-1:2022 or ASTM D1238 procedure A. The absence of ethylene comonomer in the homopolymer backbone produces a semi-crystalline morphology with higher flexural modulus and heat deflection temperature than propylene-ethylene random copolymers of comparable flow, while the higher melt flow rate permits shorter filling times in multi-cavity tooling. The grade is normally selected for rigid thin-wall packaging, caps and closures, housewares and small appliance components with wall sections from 0.45 mm to 1.2 mm. Published datasheet values are representative rather than specification limits; the lot certificate of analysis controls batch-specific melt flow, additive package and mechanical properties.

What distinguishes H200MA from lower-flow homopolymers and clarified random copolymers?

Polypropylene homopolymers with lower melt flow rates, such as 3 g/10 min or 10 g/10 min grades, have higher average molecular weight and greater chain entanglement. That molecular structure raises notched impact strength and creep resistance but also increases injection pressure and reduces flow length. When H200MA is substituted for a 10 g/10 min homopolymer in a thin-wall lid under identical injection velocity and melt temperature, filling pressure may decrease by 10–20% depending on gate geometry; published pressure-drop data for H200MA on specific tool geometries is limited, so process set-up should be validated by cavity-pressure transducers. The higher melt flow rate is produced either by reactor hydrogen control or by controlled rheology; the manufacturer’s technical bulletin states the exact route and stabilizer package.

Compared with clarified propylene-ethylene random copolymers containing 2–5 wt% ethylene, H200MA has higher stiffness and higher heat resistance but lower optical clarity and lower low-temperature impact resistance. Random copolymers are typically specified when haze below 15% on a 1 mm plaque is required, as measured by ASTM D1003; H200MA is better suited to opaque or lightly pigmented parts where top-load strength and dimensional stability under warm-fill conditions are more important than transparency.

For thin-wall packaging tools, the processing window is defined primarily by machine configuration rather than resin alone. H200MA is processed on reciprocating-screw injection-moulding machines with screw L/D ratios of 20:1 to 24:1 and compression ratios from 2.5:1 to 3.5:1. Melt temperature at the nozzle is maintained between 200 °C and 240 °C; barrel settings above 240 °C accelerate thermo-oxidative β-scission and can increase the final MFR during the cycle. Mould surface temperature is controlled from 20 °C to 50 °C. For containers with wall stock below 0.6 mm, mould temperatures of 40–50 °C and injection velocities above 200 mm/s are generally used to avoid premature freeze-off at the gate; the velocity profile must be matched to cavity-fill simulation and gate freeze-time studies.

During injection-moulding trials, hydraulic machines with closed-loop control typically operate at filling pressures between 70 MPa and 120 MPa; all-electric machines may apply lower holding-pressure profiles with faster response. Back pressure is normally set at 0.5–1.0 MPa to avoid excessive shear heating. Pre-drying is not required for resin stored in closed dry silos, but material exposed to ambient air at relative humidity above 60% should be pre-dried at 80 °C for 2–4 hours in a dehumidifying hopper dryer. Surface splay and inconsistent dosing are otherwise observed in production because condensed moisture on cold pellets entering the feed throat causes irregular screw recovery.

Linear mould shrinkage for unfilled homopolymer of this flow class is commonly taken as 1.2–1.6% during tool design and measured in accordance with ASTM D955. Shrinkage is anisotropic: flow-direction and transverse-direction values differ sufficiently to cause bowing in flat lids and rectangular bases if cooling is unbalanced. Post-mould shrinkage continues for 24–48 h. Adequate cooling time, uniform steel temperature, and gate location near the thickest section reduce warpage more effectively than raising hold pressure alone; hold pressure increases packing but also creates internal stress if the gate freezes before packing is complete.

The thermal degradation pathway in polypropylene homopolymer is dominated by β-scission of tertiary carbon radicals. At melt temperatures above 240 °C, the melt flow rate of a 20 g/10 min grade can increase by 1–3 g/10 min within 5–10 min of residence time depending on oxygen ingress and stabilizer consumption. Hot-runner manifolds with internal dead spots may create localized residence times twice the nominal machine residence time; yellowing and streaks in clear or white parts are the usual production indicators. Manifold heating zones should be independently controlled and balanced to within ±5 °C to prevent cavity-to-cavity molecular-weight variation.

Gate land lengths of 0.5–1.0 mm are typical for edge-gated lids. In hot-tip systems for thin-wall containers, tip orifice diameters below 0.8 mm can generate shear rates above 10,000 s^-1, causing shear heating that increases local melt temperature beyond the nozzle set point. Filling simulations should use capillary-rheometry viscosity data from 10² s^-1 to 10⁴ s^-1; single-point MFR is insufficient for balancing runners in multi-cavity tools because it does not capture high-shear thinning behaviour.

Thermal and mechanical property profile under ASTM/ISO test conditions

Table 1 lists representative lot-average values for REPOL PP Homopolymer H200MA. Tensile specimens are injection-moulded and conditioned at 23 °C and 50% RH for 40 h according to ISO 291. The values are typical and are not release limits; specification limits are stated in the manufacturer’s certificate of analysis for each lot.

Closures and caps moulded from H200MA are produced in high-cavitation tools with 24, 48 or 96 cavities. Short filling times are possible because the high melt flow rate limits pressure drop; however, dimensional stability depends on uniform cooling and controlled post-mould shrinkage. For beverage closures, the resin is typically assessed for organoleptic properties under EN 1622 or equivalent sensory protocols, and for stress-cracking resistance under torque, carbonation retention and removal torque tests. Removal torque should be evaluated after 24 h and 48 h of ambient annealing because post-mould shrinkage changes cap thread dimensions.

The homopolymer base resin may be used in food-contact applications when the finished article complies with FDA 21 CFR 177.1520 and EU 10/2011, subject to the specific additive formulation and end-use migration testing. Overall migration from the finished article must not exceed 10 mg/dm² under EU 10/2011 for most food simulants; specific migration limits for additives and colorants must be evaluated on the final moulded part. Food-contact compliance of the base polymer does not automatically cover masterbatch, processing aids, or post-mould surface treatments.

When regrind ratios exceed 20% in high-speed packaging production

Multiple heat histories cause chain scission in polypropylene homopolymer. When sprues and runners are reground and returned to the hopper at levels above 20 wt%, the final melt flow rate may shift by 1–3 g/10 min per pass depending on melt residence time and antioxidant consumption; published data for H200MA under specific recycling loops is limited. Lot acceptance should include MFR and yellowing index testing after regrind addition, with yellowing index measured according to ASTM E313. Regrind fractions above 30 wt% are not recommended for thin-wall parts below 0.5 mm because flow variation can produce short shots. Regrind should be pre-dried at 80 °C for 4 hours and screened through a 3 mm mesh to remove fines that can block hopper throat flow.

The grade should not be melt-blended with impact copolymer scrap or random copolymer scrap where dimensional stability is critical, because differences in crystallinity and shrinkage create differential stress and part distortion. Acidic or oxidizing purge compounds can degrade the stabilizer package; a neutral polyolefin purge or grade-compatible purge is preferred. If machine stoppage exceeds 15 min, barrel temperature should be reduced to 160 °C to limit residence-time degradation.

When evaluated against polypropylene grades with MFR values above 30 g/10 min, H200MA occupies a middle point between fill capability and mechanical integrity. In a multi-cavity cap tool with hot-runner drops, a 35 g/10 min grade may show lower fill pressure but can also exhibit flash at parting lines if clamp force is marginal. H200MA is therefore preferred when wall sections are not below 0.4 mm and sidewall or top-load rigidity is specified. Conversely, when compared with a 3 g/10 min or 10 g/10 min grade, H200MA reduces sink marks in ribbed closures because faster pressure transmission packs the part before gate freeze, but it requires tighter shot-size control on machines with worn non-return valves.

Weld-line strength in multi-gated parts is lower for homopolymer than for impact copolymer. Part designers should therefore place gates to keep weld lines away from high-stress regions, or specify a radius at the weld-line root. Published data for H200MA weld-line retention under specific load conditions is limited; a comparative break test using ISO 527-2 on welded and unwelded specimens is recommended during tool qualification.

In masterbatch addition, a polypropylene homopolymer carrier with MFR between 15 g/10 min and 30 g/10 min is recommended to maintain homogeneous dispersion. Let-down ratios of 2–4 wt% for white or custom color concentrates are typical; higher loadings may require gravimetric feeding because pellet-size and density differences cause segregation. Strongly nucleating additives can increase crystallization temperature and reduce mould shrinkage, but they may also alter haze and notched impact. Amine-based antistatic agents and low-molecular-weight antistats should be pre-evaluated for odour and plate-out because high-shear heating can volatilize these additives and deposit on mould surfaces.

Housewares and small appliance components such as rigid storage boxes, ice trays, refrigerator containers and appliance covers are moulded from H200MA when the design requires stacking strength and resistance to deformation at elevated temperatures. The heat deflection temperature at 0.45 MPa permits short-term low-stress exposure up to 105 °C; continuous service temperature in air should be limited to 95 °C unless long-term heat-ageing data on the finished part demonstrate otherwise. Stacking tests should include a 24 h top-load stress at 40 °C in accordance with ASTM D642 or ISO 12048, because creep at elevated temperature reduces measured top-load resistance relative to 23 °C values.