T30S homopolymer polypropylene, with a nominal melt flow rate of 3.0 g/10 min at 230 °C under 2.16 kg load measured according to ISO 1133-1:2022, is used as a non-nucleated single-phase base resin for talc filled and short glass fibre reinforced compounds requiring higher stiffness, elevated heat deflection temperature, and reduced mould shrinkage relative to unfilled polypropylene. Unfilled T30S typically exhibits a density of 0.90 g/cm³ per ISO 1183-1:2019, a tensile yield stress of approximately 34 MPa at 50 mm/min per ISO 527-2:2012, a flexural modulus of approximately 1,500 MPa per ISO 178:2019, and a notched Izod impact strength of approximately 2.5 kJ/m² per ISO 180/A:2000. When talc is compounded at 20 wt%, the density increases to approximately 1.05 g/cm³ and the flexural modulus rises to approximately 2,400 MPa; at 40 wt% talc, density reaches approximately 1.24 g/cm³ and flexural modulus reaches approximately 3,800 MPa. The corresponding heat deflection temperature under 1.82 MPa load, measured per ISO 75-2:2013, increases from approximately 55 °C for unfilled T30S to approximately 105 °C for a 40 wt% talc filled formulation. Short glass fibre reinforcement at 30 wt% produces a flexural modulus near 5,800 MPa, tensile strength near 85 MPa, and notched Izod impact strength near 9 kJ/m², but the anisotropic mould shrinkage and fibre orientation introduce warpage that must be managed through gate location and cooling circuit design. These property shifts are not linear with filler addition; the transition from 20 wt% to 30 wt% talc is accompanied by a disproportionate increase in melt viscosity and a reduction in the processing window, while the transition from 20 wt% to 30 wt% glass fibre is accompanied by a disproportionate increase in screw and barrel wear.

What Limits Talc Dispersion in T30S Homopolymer at Loadings Below 40 wt%?

In production-scale compounding of talc into T30S on a co-rotating twin-screw extruder with 40:1 L/D and 50 mm screw diameter, the principal dispersion limitation is not the melt temperature but the residence time distribution and the side-feed sequencing required to avoid thermal degradation of the base resin. Talc with a median particle size d50 of 2–3 µm and top cut d98 of 10–12 µm is introduced through a side feeder at zone 6 after the polymer is fully molten; barrel set points from zone 1 to zone 10 typically follow 180 °C, 190 °C, 200 °C, 210 °C, 215 °C, 220 °C, 220 °C, 215 °C, 210 °C, and 205 °C, with screw speed maintained between 300 rpm and 450 rpm. Under these conditions, the specific energy input for a 40 wt% talc compound ranges from 0.18 kWh/kg to 0.24 kWh/kg, and the melt temperature at the die is held below 235 °C to reduce chain scission of the T30S homopolymer. A critical threshold risk is the formation of agglomerates when the side-feeder screw is operated above 250 rpm while the main screw speed is below 300 rpm, because the talc is not rapidly wetted by the melt; agglomerates with diameters greater than 50 µm can survive to the final part and act as fracture initiation sites under impact loading. The vent port at zone 8 must maintain a vacuum of -0.08 MPa to remove moisture adsorbed on the talc surface; without this vacuum, residual moisture above 0.05 wt% leads to surface splay and internal voids in the moulded article. Talc dispersion quality is routinely assessed by pressure filter test or by pressed-film optical microscopy; a maximum agglomerate count of 5 agglomerates per 100 cm² at 100× magnification is considered acceptable for automotive interior substrates. Pre-drying of talc at 80 °C for 2–4 h is required when ambient relative humidity exceeds 60%; T30S itself is not hygroscopic, but the talc platelets adsorb moisture on surface silanol groups, and the moisture released in the melt impairs dispersion and lowers molecular weight retention of maleated coupling agents.

Because T30S homopolymer lacks polar functionality, the addition of talc without a suitable interfacial modifier yields only partial stress transfer, and the notched Izod impact strength of a 40 wt% talc compound can fall to approximately 2.0 kJ/m² from 2.5 kJ/m² despite the large increase in flexural modulus. Maleic anhydride grafted polypropylene at 1.0–1.5 wt% with a grafting level of 0.8–1.2 wt% maleic anhydride is typically added to improve talc wetting and to restore impact resistance to 3.0–3.5 kJ/m² under ISO 180/A:2000; the acid anhydride groups react with the hydroxyl groups on the talc surface during compounding, forming ester linkages that reduce filler-filler agglomeration and increase the interfacial adhesion. The same chemistry must be controlled to avoid premature coupling with amine-based additives; hindered amine stabilizers with free basic amines can react with maleic anhydride grafted PP, causing viscosity build-up and gel-like defects in the melt, so phenol-phosphite stabilizer packages are preferred. Stearate-coated talc grades exhibit better dispersion than untreated talc, but the stearate layer can partially volatilise at barrel temperatures above 230 °C, generating white deposits in the vent and on the die face. The injection moulding of talc filled T30S compounds uses a melt temperature of 210–240 °C, a mould temperature of 20–50 °C, and a holding pressure of 60–80 MPa; the higher thermal conductivity of the talc filled melt shortens the cooling time by 10–20% relative to unfilled T30S, but it also narrows the flow length and can produce weld lines with reduced strength. In thin-wall parts below 2.0 mm, a fast injection speed above 150 mm/s is required to prevent premature freeze-off of the talc filled melt at the gate.

When Glass Fibre Loading Reaches 30 wt%, Melt Strength and Screw Wear Become Controlling Variables

The transition from 20 wt% to 30 wt% short glass fibre in T30S homopolymer compounding introduces a set of controlling constraints that are not present at lower reinforcement levels. Chopped strand glass fibre with an initial length of 4.5 mm and a sizing chemistry based on aminosilane is side-fed after the T30S melt is established; the residual fibre length after compounding on a 40:1 L/D twin-screw extruder with distributive mixing elements in the downstream section is typically 0.4–0.8 mm. At 30 wt% glass fibre, the compound exhibits a tensile strength of approximately 85 MPa per ISO 527-2:2012, a flexural modulus of approximately 5,800 MPa per ISO 178:2019, a notched Izod impact strength of approximately 9 kJ/m² per ISO 180/A:2000, and a heat deflection temperature under 1.82 MPa of approximately 155 °C per ISO 75-2:2013. These values cannot be achieved without maleic anhydride grafted PP coupling agent at 1.5–2.0 wt%; without coupling, tensile strength drops to 55–60 MPa and notched Izod impact strength falls below 5 kJ/m² because fibre pull-out replaces fibre fracture as the dominant failure mechanism. The use of 30 wt% glass fibre also reduces the melt flow rate of the compound to approximately 1.5–2.0 g/10 min even when the base T30S has an MFR of 3.0 g/10 min, which demands injection pressures of 100–140 MPa and clamp force requirements of 3–5 kN/cm² of projected area. Screw and barrel wear is the major production concern: the hard glass fibre abrades the screw elements in the melting and mixing zones, reducing screw life to 4,000–6,000 h compared with 12,000–15,000 h for unfilled or talc filled T30S; bimetallic barrel liners and through-hardened screw elements with surface hardness above 58 HRC are necessary. Processing temperatures must be kept below 240 °C at the die to avoid degradation of the aminosilane sizing and the formation of black specks; the vacuum vent must be maintained at -0.08 MPa to remove sizing volatiles and avoid porosity. The resulting compound is particularly sensitive to gate location: glass fibres orient in the flow direction, so weld lines and end-gated parts show tensile strength losses of 40–50% relative to the unfilled flow direction strength. The table below summarises typical property ranges from industrial compounding data; exact values depend on talc particle size, fibre length retention, and coupling chemistry, and published data for this specific configuration is limited where formulation additives vary by producer.

Where the moulded component is an automotive instrument panel substrate, a glove box carrier, or a door trim insert, the selection between talc filled and glass reinforced T30S is governed by a combination of low-gloss surface requirements, dimensional stability under solar heat load, and pass/fail criteria for volatile organic compound emissions and fogging. Talc filled T30S at 20 wt% to 30 wt% talc is preferred for hidden structural carriers because the platelet filler reduces visible weld lines and produces a low-gloss grain much more readily than glass filled material; the surface gloss at 60° per ISO 2813:2014 for a 30 wt% talc filled T30S is typically below 2.0 GU, whereas a 30 wt% glass fibre compound often exceeds 5.0 GU even with textured tooling. Volatile organic compound testing according to ISO 12219-3:2012 or VDA 277 measures total carbon emissions; talc filled T30S formulations must keep total volatile organic compound emissions below 50 µg/g and fogging condensate below 2.0 mg per DIN 75201:2011 to meet automotive interior air quality limits. Glass reinforced T30S parts are used where structural stiffness at elevated temperature is required, such as front-end carriers, fan shrouds, and battery housings; the creep modulus at 80 °C for a 30 wt% glass fibre compound is approximately 3,500 MPa under ISO 899-2:2003, while talc filled material at 40 wt% is approximately 2,000 MPa. The addition of talc or glass does not automatically confer regulatory compliance; formulations intended for food contact must use resin, talc, coupling agent, and stabilisers that comply with EU 10/2011 overall migration limits of 10 mg/dm² and FDA 21 CFR 177.1520 olefin polymer requirements, while electrical and electronic applications require verification against RoHS 2011/65/EU restricted substances and REACH candidate list SVHCs. A compliance matrix is shown in the table below.

Talc Filled T30S Decomposes Rapidly Above 260°C Barrel Temperature

At barrel set points above 260 °C, T30S homopolymer and its talc filled derivatives undergo chain scission reactions that rapidly degrade the molecular weight distribution and produce low molecular weight volatiles. Differential scanning calorimetry per ISO 11357-6:2018 indicates the onset of oxidative degradation of unstabilised T30S in air at approximately 220 °C at 10 °C/min heating rate, and thermogravimetric analysis per ISO 11358-1:2022 shows weight loss beginning near 280 °C in nitrogen and near 250 °C in air. In a compounding line, the melt temperature at the die is not the whole risk; local shear heating in the kneading blocks can exceed the set point by 15–20 °C, and the presence of talc increases the melt viscosity of T30S, which intensifies viscous dissipation. When a 40 wt% talc filled T30S formulation is run with a die temperature above 240 °C, the melt flow rate increases by 15–25% within 10 min residence time, indicating molecular weight reduction; the tensile strength measured on injection moulded specimens per ISO 527-2:2012 decreases by 5–10% relative to the same formulation processed at 220 °C. Talc platelets do not generally catalyse oxidative degradation, but iron impurities in natural talc at concentrations above 0.5 wt% as Fe₂O₃ can accelerate hydroperoxide decomposition and shorten the oxidative induction time measured per ISO 11357-6:2018 by 30–50%. Stabiliser selection is therefore critical: a phenolic primary antioxidant at 0.05–0.10 wt% combined with a phosphite secondary antioxidant at 0.10–0.20 wt% is required, and acid scavengers such as calcium stearate at 0.05–0.10 wt% are added to neutralise residual catalyst residues. Avoid combination with amine-based additives because the basic nitrogen can react with maleic anhydride grafted coupling agents and with acidic decomposition products of the silane sizing on glass fibre, producing crosslinked gels that clog screen packs and generate visual defects.

Injection Moulding Shrinkage Anisotropy in 40 wt% Talc Filled T30S

Shrinkage measurements on 40 wt% talc filled T30S plaques moulded with a 2.0 mm wall thickness and tested after 24 h at 23 °C and 50% relative humidity per ISO 294-4:2018 show flow-direction mould shrinkage of approximately 0.8% and cross-flow shrinkage of approximately 1.0%, compared with 1.2% and 1.4% for unfilled T30S. The talc platelets orient predominantly in the flow direction during injection moulding, creating a mechanical anisotropy that reduces shrinkage but also produces a differential between flow and cross-flow directions that can produce warpage in large flat parts. Glass fibre reinforced T30S produces an even stronger anisotropy: a 30 wt% glass fibre compound typically has flow-direction shrinkage of 0.2–0.4% and cross-flow shrinkage of 0.6–0.9%, which is why symmetrical gate placement, balanced runner systems, and uniform cooling channel spacing of 30–50 mm are mandatory for warpage control. The mould temperature for talc filled T30S is normally set at 20–50 °C, but increasing the mould temperature to 80 °C for glass reinforced grades reduces frozen-in orientation and lowers the differential shrinkage by 10–20%, at the cost of longer cycle time. Post-mould dimensional stability is evaluated by annealing at 80 °C for 2 h followed by measurement per ISO 294-4:2018; talc filled T30S parts exhibit an additional post-annealing shrinkage of 0.1% or less, while glass reinforced parts may show 0.05% or less. Designers using T30S talc filled compounds should specify a mould shrinkage factor of 0.9–1.0% in the flow direction and 1.0–1.1% across flow; for glass filled grades, the tool design must account for the lower flow-direction shrinkage and higher cross-flow shrinkage by using central rather than side gates and by avoiding rib-to-wall ratios above 60% to prevent sink marks and voids.