Glass Filled Abs Grades Gf 10 20 And 30 Compared For Structural Parts
Glass-Filled ABS Grades: GF 10, 20 and 30 % Compared for Structural Parts
Acrylonitrile Butadiene Styrene (ABS) is an amorphous terpolymer whose unfilled grades combine moderate rigidity, impact resistance and melt processability. Short glass fibre reinforcement at nominal loadings of 10 wt%, 20 wt% and 30 wt% changes the design envelope for structural parts. Tensile and flexural moduli rise, heat deflection temperature increases, mould shrinkage falls, while notched impact and melt flow decrease. The comparative data below are consolidated from commercial datasheets and are not a substitute for grade-specific validation. Mechanical values are reported against ISO 527-1/-2, ISO 178, ISO 75-1/-2, ISO 180/1A, ISO 1183-1 and ISO 294-4. Where North American specifications are required, tensile tests are reported under ASTM D638-14.
| Property | Standard | Unfilled ABS reference | GF 10 wt% | GF 20 wt% | GF 30 wt% |
|---|---|---|---|---|---|
| Density | ISO 1183-1 | 1.04–1.06 g/cm³ | 1.10–1.15 g/cm³ | 1.18–1.24 g/cm³ | 1.26–1.34 g/cm³ |
| Tensile strength at break | ISO 527-1/-2 | 38–45 MPa | 55–65 MPa | 65–75 MPa | 75–90 MPa |
| Tensile modulus | ISO 527-1/-2 | 2.1–2.6 GPa | 4.0–5.5 GPa | 5.5–7.0 GPa | 7.5–9.5 GPa |
| Flexural modulus | ISO 178 | 2.1–2.8 GPa | 4.0–5.7 GPa | 5.6–7.3 GPa | 7.3–9.8 GPa |
| Notched Izod impact | ISO 180/1A | 15–30 kJ/m² | 8–14 kJ/m² | 7–12 kJ/m² | 6–10 kJ/m² |
| HDT at 1.82 MPa | ISO 75-1/-2 | 85–100 °C | 100–108 °C | 105–113 °C | 108–120 °C |
| Mould shrinkage, flow direction | ISO 294-4 | 0.4–0.7 % | 0.25–0.5 % | 0.20–0.40 % | 0.15–0.30 % |
What Distinguishes GF 10 From GF 20 and GF 30 in Load-Bearing Geometry?
The transition from unfilled ABS to GF 10 wt% is characterized by a disproportionate increase in flexural modulus relative to the increase in density. GF 10 wt% materials retain sufficient melt flow for thin-wall covers and snap-fit brackets, while GF 30 wt% materials approach the stiffness of some polycarbonate blends at the expense of ductility. Elongation at break under ISO 527-2 may fall from 5–10 % for GF 10 wt% to 1.5–2.5 % for GF 30 wt%. Structural parts relying on post-yield deformation or vibration damping should not automatically default to the highest glass loading.
For load-bearing bosses, ribs and snap-fit arms, flexural modulus and HDT are the primary ranking properties. A GF 20 wt% grade typically offers a flexural modulus in the range 5.6–7.3 GPa and an HDT at 1.82 MPa between 105 °C and 113 °C. This is sufficient for many interior structural brackets but below the threshold for continuous under-hood thermal exposure. GF 30 wt% grades raise HDT toward 120 °C, but published data for oven-aged structural parts indicate that oxidative embrittlement of the butadiene phase, not short-term HDT, can become the limiting failure mode above 85 °C continuous air exposure.
Creep and fatigue behavior also separate the three glass loadings. Structural parts subjected to sustained flexural load, such as industrial guards and equipment bases, are evaluated by flexural creep modulus under ISO 899-2. Glass loading increases the creep modulus under a given stress and temperature, but fibre-matrix debonding at fibre ends becomes the governing damage mode beyond approximately 0.8 % strain. Dynamic fatigue testing under ISO 13003 or equivalent flexural fatigue protocols shows that GF 30 wt% materials provide higher endurance strength in the low-cycle regime, while the advantage narrows in high-cycle fatigue because notch sensitivity at fibre bundles increases.
When Weld Lines and Shrinkage Anisotropy Govern Part Acceptance
In structural ABS parts, gate location controls fibre orientation and therefore controls local modulus, shrinkage and weld-line placement. Short glass fibres align with the melt-flow direction during the filling and packing phases. The resulting anisotropy produces lower flow-direction shrinkage and higher transverse shrinkage. For a flat GF 30 wt% cover, flow-direction shrinkage may fall between 0.15 % and 0.30 % while transverse shrinkage remains in the 0.40 % to 0.60 % range. This differential drives bowing if the mould cooling layout is not balanced. Mould cooling should be designed for turbulent flow, with a Reynolds number above 10 000, and cavity pressures should be measured with pressure transducers rather than inferred from feed temperature setpoints.
Weld lines formed around core pins or multi-gated parts exhibit lower tensile strength than the surrounding material because glass fibres orient parallel to the weld plane. Published data for absolute weld-line efficiency in glass-filled ABS is limited because the result depends on fibre concentration, wall thickness, melt temperature and gate velocity. A conservative engineering practice is to prototype a weld-line tensile bar in the same gate configuration and compare failure force under ISO 527-2. If retention falls below the design safety factor, the weld line must be relocated by valve-gated hot-runner sequencing or the part redesigned with a lower glass loading.
When flatness is critical, rapid heat-cycle moulding with mould surface temperatures up to 120 °C is used for GF 30 wt% ABS to reduce frozen-in orientation and improve weld-line strength. Cycle time increases, and published data for this specific configuration is limited across different wall thicknesses.
Drying conditions are set before melt preparation because glass-filled ABS carries moisture from fibre sizing and atmospheric exposure. Residual moisture above 0.05 % produces splay and lowers tensile strength at the gate. Desiccant drying at 80 °C for 2–4 h to a dew point below −20 °C is the standard industrial boundary. Silo storage exceeding 48 h at relative humidity above 60 % requires re-validation by ISO 15512 or an equivalent moisture-specific method.
| Processing parameter | GF 10 wt% | GF 20 wt% | GF 30 wt% |
|---|---|---|---|
| Drying temperature | 80 °C for 2–4 h | 80 °C for 2–4 h | 80 °C for 3–4 h |
| Residual moisture limit | 0.05 % maximum by ISO 15512 | ||
| Melt temperature range | 230–250 °C | 235–260 °C | 240–270 °C |
| Mould temperature range | 50–70 °C | 60–80 °C | 70–90 °C |
| MVR at 220 °C/10 kg | 15–25 cm³/10 min | 8–18 cm³/10 min | 4–12 cm³/10 min |
| Typical injection screw L/D | 20:1 | 20:1–22:1 | 22:1–24:1 with hardened assembly |
| Clamp force, 2.5–4.0 mm wall | 0.5–0.7 t/cm² | 0.6–0.8 t/cm² | 0.7–0.9 t/cm² |
The clamp force values are machine-specific and depend on projected area, flow length and wall thickness; they are not material constants. Gate dimensions for glass-filled ABS are typically larger than for unfilled ABS because the frozen-layer thickness is higher and viscosity at the gate is elevated. A direct gate or tunnel gate with a minimum diameter of 0.8 mm for GF 10 wt% and 1.2 mm for GF 30 wt% is used for small structural parts. Insufficient gate diameter produces jetting and exposed fibre bundles at the gate, which reduce tensile strength under ISO 527-2.
Melt preparation for GF 10 wt% can be performed on general-purpose injection screws, but GF 30 wt% requires a hardened screw, bimetallic barrel and abrasion-resistant check ring. The melt-temperature window is tested by ISO 1133-1:2022 MVR at 220 °C and 10 kg. The lower MVR of GF 30 wt% cannot be fully offset by raising melt temperature because the butadiene phase degrades above approximately 270 °C, releasing volatile compounds and causing brown streaking.
Screw, Barrel and Check Ring Wear Management
For GF 30 wt% materials, barrel and screw wear is the primary maintenance variable on an injection moulding line. General-purpose nitrided screws and standard check rings can exhibit accelerated flight wear and non-return valve leakage within months. Published lifetime data are machine-specific, but field observations indicate that GF 30 wt% should not be processed on unhardened screws without continuous shot-weight monitoring. Bimetallic barrels with high-chromium carbide content and screws with hard-faced flights are used where glass-filled ABS production runs exceed 3 000 h per year. Shot-weight variation greater than 0.3 % on a 200 g shot may indicate check-ring leakage, and the part should be tested for density or filler content by ISO 3451-1 before lot acceptance.
Compounding of glass-filled ABS is performed in a co-rotating twin-screw extruder with 32:1 to 40:1 L/D. Glass fibre is introduced by side-feeding after the polymer melt has formed. The side-feed location is positioned after the initial kneading block to limit fibre attrition and before downstream mixing elements to distribute the glass. Glass loading is confirmed by ash content under ISO 3451-1, with a batch tolerance typically controlled at ±2 wt%.
Limiting Moisture Uptake and Drying Deviation Before Moulding
Moisture in glass-filled ABS is not uniformly distributed; the fibre sizing has different water uptake kinetics than the ABS matrix. This produces batch-to-batch variation in melt viscosity and surface appearance if hopper residence time is too short. A desiccant-bed dryer with a return air dew point below −20 °C and a regeneration temperature above 150 °C is specified for continuous operation. The hopper should be sized for at least 2 h residence at the consumption rate, and the material should be conveyed with dry air rather than ambient plant air. Moisture analysis by ISO 15512 is preferred because simple weight-loss methods can overestimate moisture in filled systems due to fibre sizing volatiles.
Drying deviations above 0.08 % residual moisture may cause splay, jetting and reduced weld-line strength. Because glass-filled ABS is hygroscopic but not hydrolytically sensitive like polyamide, occasional moisture excursions are recoverable. However, the surface defects produced in a filled system are not cosmetic because fibre-rich regions at the surface act as stress concentrations in tensile or flexural loading.
Environmental Stress Cracking and Chemical Resistance Boundaries
Glass-filled ABS should not be specified for structural parts that contact esters, ketones, aromatic hydrocarbons or aggressive cutting fluids, because environmental stress cracking of the ABS matrix can occur at external fibre-matrix interfaces. This limitation applies to GF 10, 20 and 30 wt% grades equally, although higher glass loading increases the number of interfacial stress concentration sites. Chemical resistance validation should follow ISO 22088-2 bent-strip testing with the production-level residual stress. Glass-filled ABS is not recommended for continuous hot-water contact above 80 °C or for structural components requiring repeated steam sterilisation.
A GF 20 wt% ABS is typically specified for electrical enclosure frames and terminal blocks where UL 94 HB at 1.5 mm is acceptable and where dimensional stability under assembly screws must be maintained. The tensile modulus of a GF 20 wt% grade under ISO 527-1/-2 is sufficient to limit boss deflection, but the enclosure must be tested for comparative tracking index under IEC 60112 if creepage paths are reduced. Glass fill can lower the CTI of unfilled ABS from 600 V to product-dependent values in the 400–500 V range; the electrical safety file should not assume the unfilled ABS value without a grade-specific test.
An automotive interior structural bracket moulded from GF 10 wt% ABS is used where low glass loading preserves snap-fit ductility and where the part is not exposed to continuous air temperatures above 85 °C. The bracket is validated by tensile tests on ISO 527-2 specimens cut from the part and by heat ageing per ISO 188 at 85 °C for 500 h. For a GF 30 wt% alternative, the same bracket would show higher stiffness but lower notched impact and greater tendency for embrittlement at the gate lands. The final material decision is therefore governed by the location of weld lines and the retention of boss pull-out force after accelerated ageing.
