Scolefin 53 G 23 PP Copolymer is a chemically coupled, short-glass-fibre-reinforced polypropylene copolymer compound. The numerical suffix 23 is interpreted as the nominal glass-fibre mass fraction of 23%. The copolymer matrix differentiates the grade from glass-reinforced polypropylene homopolymer compounds by reducing low-temperature brittleness and improving energy absorption under falling-dart impact. The material is supplied in cylindrical pellet form for injection moulding and selected profile extrusion operations where elevated stiffness, reduced mould shrinkage and improved heat distortion resistance are required. Lot-specific mechanical, rheological and thermal values must be confirmed against the supplier certificate of analysis; the values discussed below are representative of a chemically coupled 23% glass-fibre-reinforced PP copolymer class and are intended for initial material screening only.

What Defines the Measured Property Envelope for a 23% Glass-Fibre-Reinforced PP Copolymer?

The representative values in Table 1 are generated on test specimens moulded according to ISO 294-1:2017 and conditioned at 23°C and 50% RH unless otherwise specified. Density and ash-content measurements provide rapid incoming quality-control markers because glass-fibre content directly affects both properties.

The melt volume-flow rate of 3.0 cm³/10 min at 230°C and 2.16 kg places the compound in the medium-flow range for glass-fibre-reinforced polypropylene. This viscosity permits filling of wall sections down to 2.0 mm when gate velocity and hold pressure are optimised. Fibre length attrition in the screw plasticating zone is not monotonic; the mean glass-fibre length decreases from the initial chopped-strand length of 3.0–4.5 mm to 0.4–0.8 mm after melt processing. The retained fibre aspect ratio controls tensile modulus and notched Charpy impact response. Back pressure above 1.0 MPa or peripheral screw speed above 200 m/min is not recommended when maximum property retention is required.

Melt processing on a typical injection moulding line requires a desiccant dryer when pellet moisture exceeds 0.1% by mass. Drying at 80°C for 2–4 h is sufficient for surface moisture removal. Barrel temperatures from feed to nozzle are set between 220°C and 260°C, while mould temperature is maintained at 20–60°C. A general-purpose screw with a length-to-diameter ratio of 18–22 and compression ratio of 2.0–3.0 is appropriate; hardened screw and barrel surfaces are specified to resist abrasive glass fibre. Back pressure in the range 0.5–1.0 MPa assists homogeneous melt development without excessive fibre attrition. Injection speed should be moderate to high to maintain uniform fibre orientation. Excessive residence time above 260°C or total cycle residence above 5 min increases thermo-oxidative degradation and shifts melt volume-flow rate outside the specified window. Shut-down and purge procedures using a polypropylene purge compound reduce the risk of carbonised deposits in hot-runner manifolds.

Production-scale moulding of this glass-filled polypropylene generally requires clamp force in the range 3–5 kN/cm² of projected part area. Hot-runner systems should use externally heated or insulated manifolds with flow channels sized for short-glass compounds. Gate diameter should not be smaller than 1.0 mm for edge gates and 1.5 mm for tunnel gates. Venting depth of 0.02–0.03 mm along the parting line prevents burn marks and allows displaced air to escape during fast injection.

When the Grade Replaces Unreinforced PP Copolymer in Semi-Structural Components

Substitution of an unreinforced PP copolymer with Scolefin 53 G 23 PP Copolymer changes the mechanical response from ductile yielding to a stiffer, lower-strain failure mode. Typical unreinforced PP copolymer tensile modulus is approximately 1200 MPa at 23°C, while the glass-reinforced grade reaches 3700 MPa under the same conditions. Heat deflection temperature under 0.45 MPa rises from roughly 85°C to 138°C, and mould shrinkage falls from 1.2–1.6% to 0.3–0.7%. The trade-off appears in multiaxial and impact-dominated loading; elongation at break decreases to 3.2%, and notched Charpy impact strength at 23°C is typically 8.0 kJ/m² compared with 20–40 kJ/m² for unreinforced PP copolymer. Ribs, bosses and snap-fits should therefore be designed around the lower elongation limit and incorporate radii greater than 0.5 mm at high-stress transitions.

Under tensile loading, the chemically coupled interface transfers stress from the polypropylene matrix to the glass fibre. Fibre pull-out is the dominant energy absorption mechanism at crack tips. At low strain rates, the material fails by fibre fracture and matrix yielding in the flow direction; cross-flow tensile strength is typically 40–60% of the flow-direction value. Weld lines formed downstream of core pins or multi-gated parts are the critical design limitation. In short-glass polypropylene, weld-line tensile strength may be reduced to 20–35 MPa even when unreinforced weld-line strength is closer to the base resin value. Placement of knit lines in low-stress areas is therefore a tool design requirement, and gate locations should be selected to avoid knit lines at boss bases or mounting ears.

For exterior applications, unstabilised glass-reinforced polypropylene undergoes surface chalking and gloss loss after short outdoor exposure. UV-stabilised black formulations are standard for exterior automotive components. Accelerated weathering under ISO 4892-2 or SAE J2527 with a xenon arc source is used to evaluate colour change and retained impact strength. Testing should be performed on plaques with moulded texture or grain to capture the influence of surface relief on degradation.

Application evaluation for Scolefin 53 G 23 PP Copolymer is centred on automotive air-management parts, front-end carrier frames, battery trays, fan shrouds, washing machine outer tubs and electrical enclosure housings where dimensional stability under load is required. In under-hood service, continuous exposure temperature is usually limited to 100–110°C for short-glass polypropylene; peak excursions above 130°C require validation of antioxidant consumption and creep behaviour according to ISO 899-1. Electrical applications require comparative tracking index testing under IEC 60112 and glow-wire testing under IEC 60695-2-11 on final moulded parts. In appliance components, the material may be evaluated where an existing unreinforced PP part shows sink marks, heat sag or dimensional drift after moisture exposure. Published data for this specific configuration in hot-water detergent environments is limited and should be generated by immersion testing under ISO 175 or ASTM D543.

Adhesion of two-component polyurethane or acrylic coatings to glass-filled polypropylene requires surface pre-treatment. Flame treatment or corona discharge can raise surface energy from 30 mN/m to 45–50 mN/m. A water-break-free surface is the minimum acceptance criterion before painting. Adhesion testing should follow ISO 2409 cross-cut or ASTM D3359 tape adhesion methods. If insert moulding or adhesive bonding is used, plasma treatment may be required after mould release agents are removed.

Thermo-Oxidative Constraints and Incompatible Additive Packages

Thermo-oxidative degradation of the polypropylene matrix is the primary processing constraint. Melt temperatures above 260°C accelerate chain scission, reduce molecular weight, and increase melt volume-flow rate beyond the initial specification. Residual oxygen in the feed throat combined with residence times above 5 min can generate aldehyde and ketone degradation products. Nitrogen blanketing or vacuum venting is therefore recommended for long-cycle, hot-runner operations. The glass-fibre reinforcement is chemically coupled to the copolymer matrix through a maleic anhydride-grafted polypropylene interface. Basic amine-containing additives, high-pH mineral fillers and certain metal stearates can interfere with interfacial adhesion and should be introduced only after melt-flow and tensile modulus stability are confirmed. Regrind use is generally limited to 20–30% by mass of the shot weight; higher regrind fractions reduce fibre aspect ratio and lower tensile modulus.

Continuous-use temperature for short-glass polypropylene is limited by oxidative degradation of the matrix. At 120°C, under-stabilised grades lose tensile strength rapidly; heat-stabilised grades are specified for under-hood service. Long-term thermal ageing according to ISO 188 or ASTM D3045 is required to confirm retained tensile strength after 1000 h at the service temperature. A retention threshold of 80% of initial tensile modulus is commonly used for initial material qualification.

Water absorption of glass-reinforced polypropylene is low, typically 0.05–0.10% at saturation at 23°C according to ISO 62. The material resists many aqueous acids, alkalis and detergent solutions, but strong oxidising acids such as concentrated nitric acid require separate evaluation. Solvent resistance to aliphatic hydrocarbons is limited; prolonged contact with xylene or toluene can swell the polypropylene matrix and must be tested by ISO 175 immersion with dimensional change recorded at 24 h and 168 h.

Regulatory screening for European and North American markets is summarised in Table 2. The matrix does not replace part-specific compliance testing; final article testing must be conducted on the finished component under the applicable directive or regulation.

Relative to a 30% glass-fibre-reinforced polypropylene compound, Scolefin 53 G 23 PP Copolymer has a lower density, lower melt viscosity and lower tensile modulus. The 23% glass loading is selected when the stiffness of an unreinforced grade is insufficient but the higher warpage and embrittlement of a 30% glass grade are unacceptable. Compared with talc-filled PP copolymer compounds at similar filler loading, glass-fibre reinforcement provides higher tensile strength and heat distortion resistance but produces more pronounced anisotropic shrinkage. Where published data for this specific configuration is limited, comparative moulding trials under ISO 294-1 should be used to establish part-specific shrinkage and warpage compensation.