Pp Datasheet Library Properties Table By Grade Family
The PP Datasheet Library: Properties Table by Grade Family is structured around melt-state rheology, crystalline morphology, comonomer content, and additive formulation rather than nominal brand designation. A grade family field separates isotactic homopolymer, random ethylene-propylene copolymer, and heterophasic impact copolymer because a melt flow rate of 12 g/10 min may correspond to a tensile yield stress of 34 MPa in a homopolymer, 26 MPa in a random copolymer, and 21 MPa in a heterophasic impact copolymer. The property table therefore binds each row to a test method, specimen conditioning protocol, and strain rate. Missing data in a supplier datasheet is not a neutral omission; it frequently indicates that the grade has not been characterized under the stated condition or that the value lies outside the validated production window.
For injection-moulded specimens, ISO 3167 Type A or ASTM D638-14 Type I tensile bars are usual, but data generated from machined plaques cannot be compared directly because of skin-core morphological variation. Sheet extrusion grades are better characterized on extruded film or sheet according to ISO 527-3, while pipe grades require long-term hydrostatic testing outside the scope of a room-temperature datasheet. Comparative tables should therefore include the specimen preparation route as an explicit field.
| Property | Test method | Homopolymer injection | Random copolymer | Impact copolymer | High-MFR fibre/spunbond |
|---|---|---|---|---|---|
| Density | ISO 1183-1 | 0.90–0.91 g/cm³ | 0.89–0.91 g/cm³ | 0.89–0.91 g/cm³ | 0.90–0.91 g/cm³ |
| Melt flow rate, 230°C/2.16 kg | ISO 1133-1 | 3–15 g/10 min | 2–25 g/10 min | 1–35 g/10 min | 25–100 g/10 min |
| Tensile yield stress | ISO 527-2 | 30–37 MPa | 24–32 MPa | 18–28 MPa | 30–35 MPa |
| Tensile strain at yield | ISO 527-2 | 8–12% | 10–15% | 5–10% | 8–12% |
| Flexural modulus | ISO 178 | 1200–1800 MPa | 700–1200 MPa | 900–1500 MPa | 1300–1600 MPa |
| Notched Charpy impact, 23°C | ISO 179-1/1eA | 2–4 kJ/m² | 5–12 kJ/m² | 15–60 kJ/m² | 2–3 kJ/m² |
| Notched Charpy impact, −20°C | ISO 179-1/1eA | 1–2 kJ/m² | 2–4 kJ/m² | 7–15 kJ/m² | 1–2 kJ/m² |
| Vicat softening temperature A50 | ISO 306 | 150–156°C | 125–140°C | 140–155°C | 150–155°C |
| Heat deflection temperature B, 0.45 MPa | ISO 75-2 | 90–110°C | 65–85°C | 80–100°C | 85–95°C |
| Mould shrinkage | ISO 294-4 | 1.0–1.6% | 0.8–1.2% | 0.8–1.4% | 1.0–1.8% |
The ranges are representative of unfilled commercial grades; specific supplier datasheets may report values outside these ranges depending on nucleation, additive package, and processing history.
How Does Melt-Flow Ratio Alter the Utility of a PP Grade Family in Thin-Wall Injection Moulding?
Thin-wall electronic connector housings and disposable medical articles require melt flow rates from 30 g/10 min to 100 g/10 min on the ISO 1133-1 bench, but the practical injection pressure is governed by capillary viscosity at shear rates above 1,000 s⁻¹. Hydraulic injection units with clamp force between 1,500 kN and 4,000 kN typically limit packing pressure to 800–1,200 bar; high-flow homopolymer grades reduce fill pressure by 20–35% relative to medium-flow grades of the same density. However, notched Charpy impact at 23°C often falls below 2.5 kJ/m² for these high-flow grades, and the ductile-brittle transition can occur between 0°C and 10°C. Datasheet libraries that separate melt flow index from impact and modulus values allow a design engineer to reject a high-flow homopolymer for a living hinge or snap-fit without confusing it with a random copolymer of the same nominal flow.
In production-scale injection moulding, the screw recovery time and melt temperature must be correlated with the datasheet MFR because a 15 g/10 min grade processed at a barrel profile of 210°C to 250°C can still exhibit gate freeze before full packing if the wall thickness is below 1.0 mm. Direct-gated tensile bars moulded at high injection velocity may show yield stress 5–10% higher than datasheet values because of flow-induced orientation in the skin layer. Conversely, a low-pack, high-speed setting can create internal voids and reduce notched impact. For this reason the property table should include moulding conditions, not merely nominal values.
When Thermoforming Grade Selection Requires a Narrow Melt-Strength Window
Thermoforming PP sheet extrusion uses grades with MFR from 1 g/10 min to 3 g/10 min; a grade above 5 g/10 min can sag uncontrollably in the radiant oven of a shuttle station. Sheet surface set points are commonly between 260°C and 300°C, but the core must reach no more than 160°C to 175°C before forming. The critical process window is typically ±5°C in lower oven zones, beyond which formed cup wall thickness varies by more than 0.3 mm and thinning at the clamp ring becomes visible. Standard HDT at 0.45 MPa according to ISO 75-2 is not a reliable ranking tool for this failure mode because it applies a flexural load rather than extensional sag. High-melt-strength PP grades improve sag resistance but may require higher sheet temperature, narrowing the thermoforming window at the upper end if the random copolymer skin starts to stick to the plug. Therefore a property table for thermoforming should include melt tension in centinewtons, extensional viscosity at strain rates below 1 s⁻¹, and sheet haze if the application requires clarity. Published data for the interaction between oven zoning and plug material in high-melt-strength PP is limited.
Because impact copolymer datasheets in a PP library typically separate notched Charpy at 23°C and −20°C, they rarely report weld-line strength. In a two-gate tool, the rubber phase in an impact copolymer can orient parallel to the weld plane, reducing notched Charpy from an unfilled value of 25 kJ/m² to as low as 6 kJ/m² when measured at 23°C. This degradation is not detected by the standard ISO 179-1 single-gate specimen. Flow simulation with isotropic mechanical data then overestimates crash-can or bumper bracket performance. The property table by grade family must therefore identify the gate configuration used for impact data and, where available, the weld-line test method ISO 294-5 or equivalent.
What Limits the Use of High-Melt-Flow PP in Cast Film Coextrusion?
Cast film coextrusion of PP sealing webs uses random copolymer layers with melting peak temperatures from 126°C to 142°C by differential scanning calorimetry. When the seal layer is displaced by a high-melt-flow homopolymer with MFR above 25 g/10 min, the melt curtain can exhibit draw resonance at haul-off speeds exceeding 120 m/min. Neck-in increases with melt temperature, and die width must be oversized by 15–25% to maintain final web width. The property table for film grades should list melt tension and melt strength, but many supplier datasheets omit these because the standard MFR test at low shear does not reflect extensional behaviour in the air gap. Coextrusion with high-melt-strength PP resins is possible, but process stability then depends on die lip gap and vacuum box settings, which are rarely represented in a material datasheet.
Spunbond nonwoven lines operate best with fibre-grade PP having MFR from 35 g/10 min to 60 g/10 min, extruded at 220°C to 250°C and filtered at 40 µm or finer. Filament diameter from 15 µm to 25 µm depends on melt pump pressure, quench air velocity, and grade polydispersity. Base PP moisture uptake is below 0.1% at 50% RH, but additive concentrates and pre-compounded colourants may require drying at 80°C for 2–4 h. The datasheet library should separate fibre-grade thermal stabilizer packages from injection moulding packages because fibre spinning exposes the melt to larger surface area and higher draw rates, accelerating thermo-oxidative degradation at the spinneret.
Pipe Extrusion Grades and Long-Term Hydrostatic Strength Data
Pipe extrusion grades of PP-H, PP-B, and PP-R are separated in a datasheet library by MFR values near 0.3–0.5 g/10 min and by long-term hydrostatic design stress rather than by single-point tensile properties. ISO 9080 extrapolation is required for 50-year service life predictions; PP-R systems may be designed with a hydrostatic design stress of 3.2 MPa at 70°C, but the short-term notched Charpy value does not predict slow crack growth resistance. The property table should include the minimum required strength curve class, fusion compatibility, and oxygen-barrier additive restrictions. On a single-screw extruder with a grooved barrel and L/D ratio of 30:1 to 37:1, melt temperature deviations greater than ±10°C can alter wall thickness accuracy and pipe diameter. The datasheet alone cannot qualify a resin for pressure piping; long-term hydrostatic testing under ISO 1167-1 with specified end caps and test temperatures is mandatory.
Food-contact PP grades in the library are differentiated from general-purpose grades by migration testing under EU Regulation 10/2011 and FDA 21 CFR 177.1520. Specific migration limits for total migration are typically 10 mg/dm² for food-contact plastics. Medical devices using PP may require USP <661.1> or ISO 10993-5 cytotoxicity evaluation; these are not material properties but finished-device validations. The properties table by grade family identifies additive systems, catalyst residues, and lot-to-lot variability where available. Published data for specific film extrusion structures combining high-melt-strength PP and random copolymer skins is limited.
