MOSTEN (ORLEN Unipetrol) PP homopolymer comprises isotactic polypropylene grades manufactured by polymerisation of propylene with a supported coordination catalyst. The resin is supplied as pelletised or powdered product and is characterised by a semi-crystalline morphology with a density in the range of 0.895–0.910 g/cm³ when measured according to ISO 1183-1. The homopolymer designation distinguishes the product from copolymer grades in the MOSTEN portfolio: no ethylene or other α-olefin comonomer is deliberately incorporated to create a rubber phase. As a result, the material exhibits higher stiffness and hardness than random or impact copolymers at equivalent melt flow rates, while low-temperature impact strength and optical clarity are lower. Typical conversion routes include injection molding, sheet and pipe extrusion, biaxially oriented film, raffia tape, and spunbond or staple fibre. The commercial portfolio is segmented by nominal melt flow rate and additive package. Representative injection-molding designations include MOSTEN GB 003, MOSTEN GB 005 and MOSTEN GB 022 for low, medium and high-flow general-purpose homopolymer requirements.

Material identity and portfolio structure

Production is located at the Litvínov site in the Czech Republic. The homopolymer series is sold in natural, nucleated, antistatic and UV-stabilised variants depending on end-use requirements. Published technical datasheets for general-purpose injection grades identify nominal melt flow rates of 3 g/10 min, 5 g/10 min and 22 g/10 min for MOSTEN GB 003, MOSTEN GB 005 and MOSTEN GB 022 respectively, measured at 230 °C/2.16 kg in accordance with ISO 1133-1:2022. Extrusion and fibre grades are typically supplied in the lower MFR segment, from 0.3 g/10 min to 18 g/10 min, where melt strength and orientation behaviour are more important than flow length. The pelletised form is the default for injection molding and film extrusion; powder is used where dry blending with fillers, pigments or peroxides is required.

Because a single homopolymer grade cannot cover all conversion routes, the property window below is drawn from published polypropylene homopolymer technical literature and commercial material datasheets. It should be treated as a portfolio-wide reference rather than a grade-specific specification for one MOSTEN designation.

The low-flow homopolymer segment, nominally 0.3–3 g/10 min, is used for sheet, pipe and thick-wall extrusions where sag resistance and melt strength are necessary. Medium-flow grades from 3–8 g/10 min are used for closures, caps, housewares and general injection molding; high-flow grades from 12–25 g/10 min are used for thin-wall food packaging, nucleated containers and long-flow multicavity tools. The exact upper limit of MFR for a given tool is determined by flow length, wall thickness and injection pressure. A shift from 12 g/10 min to 22 g/10 min is often made when filling pressure is excessive, but the lower molecular weight also reduces notched Charpy impact.

What distinguishes homopolymer from random and impact copolymer grades?

Comparative data for the MOSTEN product family follow the general structure-property relationship of isotactic polypropylene. Homopolymer grades have a higher crystalline fraction than random copolymers because the absence of ethylene co-units reduces chain defects that interfere with lamellar packing. Differential scanning calorimetry according to ISO 11357-3 typically records a melting peak near 160–165 °C for homopolymer grades, whereas random copolymers often show broadened or bimodal melting endotherms between 130 °C and 148 °C. Tensile yield stress and flexural modulus of homopolymer therefore remain higher by approximately 10–20% at equal melt flow rate, while notched Charpy impact strength at -20 °C may remain below 2 kJ/m², compared with impact copolymers containing an ethylene-propylene rubber phase that can exceed 6 kJ/m² under ISO 179-1/1eA. Optical haze also differs: random copolymers can achieve haze values below 10% in 1 mm injection-moulded plaques, whereas unfilled homopolymers typically range from 20% to 60% depending on nucleation and surface finish. The replacement boundary is therefore defined by three conditions: homopolymer is selected where stiffness, heat deflection temperature and creep resistance control the application; random copolymer is selected where contact clarity and low sealing initiation temperature are required; impact copolymer is selected where low-temperature ductility and drop-weight impact strength dominate.

In rigid packaging closures, the selection of homopolymer over random copolymer is driven by torque retention and stress cracking resistance in contact with fats and oils. Injection-molded closures produced from medium-flow homopolymer grades are tested for strip torque and removal torque according to ASTM D2063 or customer-specific procedures; the higher flexural modulus of homopolymer allows reduced sidewall thickness while maintaining top-load capacity. Long-term environmental stress cracking resistance in detergent and surfactant formulations is evaluated by cyclic torque testing after storage at 40 °C and 70% RH for 14 days. Published data for specific MOSTEN homopolymer grades under aggressive surfactant exposure is limited, so closure producers perform formulation-specific compatibility screening.

Biaxially oriented polypropylene film produced from homopolymer grades with MFR 2–3 g/10 min is oriented in machine and transverse directions at draw ratios of 5:1 to 10:1. Homopolymer film develops high tensile modulus but remains heat-sealable only at high temperatures; therefore coextruded seal layers of random copolymer or terpolymer are used. The homopolymer core layer is selected for stiffness, moisture barrier contribution and high gloss after cavitation or metallisation. Thickness uniformity across the web is maintained by controlling melt flow rate variability and gel count, because unmelted or crosslinked particles produce optical defects in film thinner than 20 µm.

In raffia tape and fibre conversion, water-bath and hot-air stretching are performed at draw ratios from 1:5 to 1:8. Homopolymer grades in the 3–5 g/10 min MFR range are typically drawn at temperatures between 120 °C and 150 °C; higher draw ratios increase tensile strength at break but reduce transverse toughness. Processors adjust screw speed and water-bath temperature to maintain tape fibrillation resistance and weaving efficiency, because excessive orientation can promote longitudinal splitting during loom operation. These process boundaries are not fixed by melt flow rate alone; additive package, molecular weight distribution and thermal history contribute to orientation behaviour.

The conversion behaviour of MOSTEN homopolymer is governed by melt flow rate and thermal stability. Unfilled homopolymer does not normally require pre-drying because equilibrium moisture uptake at 23 °C and 50% RH is below 0.03% by mass. If sacks have been opened in high-humidity storage or chilled pellet surfaces have developed condensation, desiccant drying at 80 °C for 3–4 h is applied before extrusion or injection molding. Melt temperatures at the nozzle are ordinarily set between 210 °C and 250 °C for injection molding; sheet and cast film extrusion commonly uses 210–240 °C, and biaxially oriented film lines may require 235–250 °C at the die. Thermo-oxidative degradation accelerates above 260 °C; melt residence time above 250 °C should therefore be limited to 5 min. Screw L/D ratios of 20:1 to 24:1 with three-zone general-purpose screws are adequate for unfilled grades, while high-flow injection grades benefit from mixing sections to distribute nucleating agents and antistats without excessive shear heating.

Mold shrinkage of unfilled homopolymer injection grades generally falls in the range of 1.0–2.0% in the flow direction and 1.2–2.2% transverse to flow when measured on plaques after 48 h at 23 °C in accordance with ISO 294-4. Packing pressure, wall thickness and gate freeze time are more influential than small MFR differences; processors compensate by increasing holding pressure from 50 MPa to 80 MPa for stiff-flow grades and by using lower mold temperatures of 20–40 °C for thin-wall packaging to reduce cycle time. Nucleated homopolymer grades crystallise more rapidly and generally show a 10–20% increase in flexural modulus measured by ISO 178, with a corresponding reduction in haze and improved cycle-time consistency in multicavity tools.

When narrow processing windows govern thin-wall injection molding

Thin-wall containers and closures with flow-path thickness below 0.8 mm require homopolymer grades with high melt flow rates, typically above 20 g/10 min (ISO 1133-1, 230 °C/2.16 kg). The processing window narrows because a low-flow grade freezes before filling the cavity, while excessive melt temperature or shear heating causes molecular weight reduction and surface splay. On production-scale injection molding machines with clamp force ratings between 2500 kN and 6000 kN, multicavity hot-runner tools with flow-length-to-thickness ratios greater than 200:1 often require a reverse barrel temperature profile: feed zone 200 °C, compression 230 °C, metering 240 °C, nozzle 245 °C. Injection velocity is maintained between 150 mm/s and 250 mm/s, and holding pressure is set at 60–80 MPa to obtain gate freeze before part ejection. Adiabatic shear heating in thin gates can raise the local melt temperature by 10–20 °C; the nozzle setpoint is therefore reduced by 10 °C when short shots are absent but gate blush or burning marks appear. Because high-flow homopolymer grades have lower molecular weight, notched Charpy impact at 23 °C may fall below 2 kJ/m² (ISO 179-1/1eA), so the design must avoid impact-dominated loadings unless the part geometry provides reinforcement through ribs or curved walls.

For fibre and tape production, the critical boundary is not flow length but melt strength and draw resonance. Homopolymer grades in the 3–18 g/10 min MFR range are drawn at line speeds that may exceed 300 m/min on commercial tape lines; the MFR is selected to maintain stable bubble or sheet geometry without excessive orientation-induced fibrillation. Published data for specific MOSTEN homopolymer configurations on ultra-high-speed lines is limited, so start-up conditions are normally derived from resin supplier processing guides and lot-specific MFR and rheology data.

Compliance matrix and regulatory boundaries

MOSTEN homopolymer grades may be supplied with conformity documentation for food-contact, medical, electrical and automotive applications, but the compliance status is grade-specific and must be confirmed against the supplier declaration for the exact formulation and lot. Food-contact evaluations are conducted under Regulation (EU) No 10/2011 and its amendments, with overall migration tested according to the EN 1186 series and specific migration according to EN 13130. For pharmaceutical packaging, relevant pharmacopoeial monographs such as Ph. Eur. 3.1.3 and USP <661.1> are applied by the converter; biocompatibility assessment may follow ISO 10993-1 if the molded component is a medical device or part of one. Electrical and electronic applications are supported by RoHS Directive 2011/65/EU documentation when required, and the resin falls under the general registration obligations of Regulation (EC) No 1907/2006 (REACH).

For automotive interior and under-bonnet applications, long-term heat aging is evaluated according to ISO 188 or OEM-specific methods at temperatures from 90 °C to 150 °C depending on location. A homopolymer grade with high initial flexural modulus may retain stiffness after aging, but oxidative embrittlement at the surface can reduce notched Charpy impact before visible discoloration occurs. Users should therefore qualify lot-specific additive packages by oven aging of moulded plaques rather than relying solely on short-term mechanical data. Published data for specific MOSTEN homopolymer grades in long-term hot-air aging is limited, and converter qualification remains mandatory.