Tianjin Dagu SAN DG-AS106 is a styrene-acrylonitrile copolymer moulding grade produced by Tianjin Dagu Chemical Co., Ltd. The DG prefix identifies the manufacturer, AS denotes the acrylonitrile-styrene polymer family, and 106 is a producer-specific viscosity or modification index whose exact correlation with melt flow rate and acrylonitrile content must be confirmed against the lot certificate. The resin is intended for injection moulding of transparent and translucent rigid parts where the material must provide higher stiffness, heat resistance, surface hardness and chemical resistance than general-purpose polystyrene while retaining better clarity than most ABS grades. Published data for this specific configuration is limited; therefore, numerical values in this technical introduction are drawn from commercial SAN resin ranges prepared under ISO 294-1 and reported according to ISO 10350-1, and they are not a substitute for DG-AS106 lot-specific data.

The styrene-acrylonitrile product class is covered by ISO 19064-1:2015 and ASTM D4203-17. Designation under ISO uses a standardized block system that describes polymer, processing method, melt volume-flow rate, impact strength and additional information. Because DG-AS106 is a commercial grade name, the relevant specification is the producer’s technical data sheet referenced to those designation blocks. Purchasers evaluating DG-AS106 as a direct replacement for existing GPPS or a transparent ABS grade should compare not only a single property but the full data set from the same specimen preparation state, preferably ISO 294-1 multipurpose test specimens.

Which Physical Property Set Separates SAN from GPPS and ABS?

Commercial styrene-acrylonitrile copolymers derive their higher rigidity and solvent resistance from the polar acrylonitrile comonomer. In standard SAN grades, acrylonitrile content commonly falls between 24 % and 28 % by mass. The acrylonitrile units raise the glass transition temperature, increase tensile modulus, and provide resistance to aliphatic hydrocarbons, mineral oil, fats, weak acids and weak alkalis compared with GPPS. The absence of a discrete polybutadiene rubber phase, as used in ABS, preserves optical transmission but limits notched impact toughness. Under tensile testing to ISO 527-2, standard SAN moulding compounds typically show tensile modulus from 3500 MPa to 3800 MPa and tensile stress at yield from 65 MPa to 75 MPa, whereas GPPS generally shows tensile modulus below 3300 MPa and ABS often below 2600 MPa because its rubber phase reduces stiffness. Flexural modulus for SAN measured by ISO 178 is commonly 3600 MPa to 4000 MPa; the exact DG-AS106 value remains subject to supplier data.

Notched Charpy impact performance is the most significant limitation of SAN. Tested at 23 °C by ISO 179-1/1eA, standard SAN grades typically produce 1.5 kJ/m² to 2.5 kJ/m², while ABS may exceed 15 kJ/m² to 30 kJ/m². DG-AS106 should not be used in impact-dominated applications unless the part has a generous wall thickness, no sharp internal corners, and the operating temperature remains well above the ductile-to-brittle transition. For transparent applications requiring higher toughness, polycarbonate or transparent ABS may be necessary; however, those materials introduce different chemical resistance and processing constraints. The comparison is summarized in Table 1 for representative material classes.

Typical SAN applications for DG-AS106 include transparent covers, appliance panels, cosmetic packaging, medical device housings that do not require impact-dominated performance, water filter vessels, scale housings, and laboratory ware. The material is selected when the finished part must resist cracking in contact with household or industrial oil-based cleaners but must not yellow at the same rate as GPPS under light exposure. Resistance to environmental stress cracking is evaluated by exposing moulded test bars to a specific chemical under fixed strain, such as ISO 22088-3 bent-strip method. Aliphatic hydrocarbons and mineral oil generally produce less stress cracking in SAN than in GPPS; polar ketones, esters, aromatic hydrocarbons and chlorinated solvents are outside operational limits for continuous contact.

Chemical resistance should be interpreted with strain applied. SAN withstands many aliphatic hydrocarbons, mineral oils, vegetable oils, dilute acids and alkaline solutions at moderate temperature. However, aromatic hydrocarbons such as benzene and toluene, chlorinated solvents, ketones including acetone and methyl ethyl ketone, and esters including ethyl acetate will swell or dissolve SAN and must not be used for continuous contact. The same property that provides resistance also reduces the number of solvent bonding options; joining methods suitable for SAN are limited to methylene chloride-based solvents under controlled process ventilation, adhesive bonding with cyanoacrylate or structural acrylics after corona or plasma treatment, or hot-plate welding. Ultrasonic welding is possible for DG-AS106 parts if joint design uses shear joints and amplitude is limited because amorphous SAN melts sharply at the glass transition.

Thermal Stability Limits Are Set by Acrylonitrile Content and Shear Work

The processing window for SAN is narrower than for GPPS because the acrylonitrile comonomer is thermally sensitive and can regenerate residual monomer or yellow at excessive temperatures. Melt temperature above 250 °C and residence time beyond 6 min to 8 min should be avoided. The practical consequence is that DG-AS106 should be processed with the smallest buffer of molten material in the barrel, no excessive screw recovery speed, and no dead spots in the nozzle or hot runner manifold. The thermal degradation pathway produces colour shift from water-white to yellow and may increase the detectable free-acrylonitrile level; both are quality-defect indicators on transparent mouldings.

Pre-drying in a desiccant dryer at 80 °C ± 5 °C for 2 h to 4 h to a residual moisture content below 0.02 % by weight is a standard starting point for SAN moulding resins. Moisture introduced into the melt disrupts nitrile groups and contributes to splay, surface bubbles, reduced tensile strength and elevated residual odour. In high-humidity environments above 60 % relative humidity, predrying should be extended and hopper drying should not be used as a substitute for desiccant dryers because the required dew point is typically below -30 °C.

Rheological Envelope and Barrel Temperature Profile

On a conventional reciprocating screw injection moulding machine with a general-purpose screw of 20:1 L/D ratio and a non-return ring, SAN grades are usually started with barrel temperatures of 200 °C at the feed throat, 220 °C to 230 °C in the compression zone, and 230 °C to 240 °C at the nozzle. The measured melt temperature should be maintained between 215 °C and 250 °C. Mould temperature between 40 °C and 80 °C balances cycle time, surface gloss and moulded-in stress. Back pressure from 0.3 MPa to 0.7 MPa assists melt homogenization, while screw surface speed below 0.5 m/s limits shear heating. These values are initial setup guides for SAN, not DG-AS106-specific datasheet conditions.

Filling speed should be adjusted so that flow-front velocity is stable. In practice, parts with nominal wall thickness below 2 mm may require injection speeds above 50 mm/s and melt temperatures near the upper end of the range; thicker sections above 4 mm should use lower injection speeds to avoid jetting and internal sink marks. Holding pressure of 60 % to 80 % of peak injection pressure, applied until gate freeze, reduces shrinkage variation. Gate freeze time is measured by part-weight stabilization; switching from holding to cooling too early creates voids and high birefringence in polarised light.

Shear heating effects are measurable in reciprocating screw machines. A screw recovery speed of 80 rpm may increase melt temperature by more than 15 °C relative to barrel settings in high-viscosity SAN; that increase can push the melt beyond the degradation threshold. Consequently, the barrel set point may need to be reduced when using high screw speed, and melt temperature should be verified with an insertion pyrometer. The same applies to hot runner systems with small drops: shear rates above 10 000 s⁻¹ may produce local overheating even when nozzle temperature is within specification.

Gate design for SAN should avoid sharp transitions and dead spots. Tunnel and edge gates can be used; for transparent parts, direct sprue gates often improve flow symmetry but leave gate vestige. Hot-runner manifolds should be externally heated and fully balanced, with valve gates or open tips sized for the material’s viscosity. Small gate diameter below 1 mm can cause premature freeze, high pressure drop, and melt fracture. If the gate is too large, gate-freeze time extends, reducing cycle efficiency. The optimum gate diameter is determined by part wall thickness and flow length; a wall thickness of 2.5 mm commonly tolerates gate diameters from 1.0 mm to 1.5 mm. Full-flow analysis using pressure-volume-temperature data and no-flow temperature provides better data than generic values.

Mould temperature uniformity is critical in thick transparent parts. Differential cooling produces anisotropic shrinkage and birefringence, which can be assessed with a polariscope. If residual stress is visible, raising mould temperature to the upper end of the 40 °C to 80 °C range and reducing injection pressure may help. However, high mould temperature increases cycle time. Conformal cooling or high-conductivity mould inserts are used on production runs where optical anisotropy must be controlled across batches.

Batch-to-batch viscosity variation is a common production bottleneck. The producer’s certificate of analysis should report melt volume-flow rate under ISO 1133-1:2022 at the same temperature and load used for incoming quality control, typically 220 °C and 10 kg for SAN with a die of 2.095 mm diameter. If MVR variation exceeds the agreed range, cavity short shots or flash may alternate. Incoming resin should be sampled, dried, and checked against the material’s lot certificate before release to production; a capillary rheometer test at 230 °C over the shear-rate range of 100 s⁻¹ to 1000 s⁻¹ can reveal lot-to-lot differences hidden by single-point MVR.

When Replacing GPPS or ABS with DG-AS106

When DG-AS106 replaces GPPS, the part can generally be designed with modestly thinner walls because SAN provides higher stiffness and heat resistance. However, mould shrinkage is different from GPPS; typical SAN mould shrinkage in flow direction is often 0.4 % to 0.6 %, while GPPS may be 0.3 % to 0.5 % depending on part geometry and holding time. Ejection may be more difficult with SAN because the harder surface can scuff if draft angles are below 0.5 °. Tool-cooling layout must be uniform because non-crystalline SAN exhibits high melt viscosity and heat capacity; uneven mould temperatures cause differential shrinkage, warpage and residual stress visible as photoelastic fringes.

When DG-AS106 replaces an ABS part, the first point to verify is notched impact strength. If the existing ABS part survives drop-impact testing at room temperature, the SAN replacement may not, especially at low temperatures below 0 °C. The advantage of the replacement is clarity and better chemical resistance to hydrocarbon-based greases; ABS parts are tougher but often opaque and more susceptible to environmental stress cracking in contact with certain oils and solvents. A direct replacement should include notched Charpy testing under ISO 179-1/1eA, tensile creep testing under ISO 899-1, and environmental stress-cracking testing under ISO 22088-3 using the intended service chemical.

Compared with high-acrylonitrile SAN grades, DG-AS106 is expected to process at lower melt temperature and lower injection pressure if its viscosity index is standard. High-acrylonitrile SAN with AN content above 30 % provides better barrier and chemical resistance but yellows more readily and has a higher glass transition and melt viscosity. Conversely, low-acrylonitrile SAN grades may have lower heat resistance and chemical resistance but better flow and less colour shift. The exact position of DG-AS106 within this trade-off must be read from the producer’s data sheet; the grade code alone does not define AN content.

Styrene-acrylonitrile polymers may be evaluated for food-contact use under specific regulatory frameworks. In the United States, one possible reference is 21 CFR 181.32, but the grade must meet residual acrylonitrile monomer restrictions and intended end-use conditions. In the European Union, compliance is assessed under Regulation (EU) No 10/2011 on plastic materials and articles intended to come into contact with food, together with Regulation (EC) No 1935/2004. RoHS assessments are conducted against Directive 2011/65/EU Annex II restricted substance limits; REACH SVHC duties are governed by Regulation (EC) No 1907/2006. A grade-specific supplier certificate is required for each lot and each colour concentrate, because pigments and processing aids may alter the regulatory profile.

Regrind for DG-AS106 should be limited to 20 % by mass in transparent applications unless documented on the actual production line, because repeated heat history raises yellowing and lowers notched Charpy impact. Purging should be performed with a styrene-based purge compound or the incoming SAN itself; polyolefin residues create visible streaks and delamination. Avoid combination with amine-based processing aids, acetal homopolymer residues, and PVC residues because these materials can generate discolouration, gassing, or plate-out on mould surfaces at SAN processing temperatures. Dry-air conveying and closed hopper loading are recommended when relative humidity exceeds 60 %.

In a transparent medical diagnostic housing that is repeatedly wiped with isopropanol or quaternary ammonium disinfectants, the SAN grade should be tested under ISO 22088-3 bent-strip conditions with the actual disinfectant concentration and temperature. If the lot-specific Vicat softening temperature is 105 °C, post-moulding stress-relief annealing at 15 °C below Vicat for 30 min may reduce stress cracking, but dimensional changes must be checked against the drawing tolerance. Published data for this specific configuration is limited; qualification parts should be moulded on the intended production machine and not on a laboratory specimen press.