Kumho Petrochemical SAN 315NTR is supplied as a natural transparent styrene-acrylonitrile random copolymer pellet, positioned within the high-flow injection-moulding segment of the SAN family. The grade is not described in open literature by a complete ISO designation; therefore specification must be tied to the lot certificate and the supplier’s published technical datasheet. Typical SAN copolymers of this class contain 24–32 % acrylonitrile by mass, with the balance predominantly styrene and a low level of processing stabilizers. A class-level density range of 1.07–1.08 g/cm³ is determined by ISO 1183-1:2019 method A, and equilibrium water absorption in 23 °C water remains near 0.2–0.3 % by ISO 62:2008. For a 3 mm injection-moulded natural plaque, SAN grades of this category typically transmit 88–90 % of visible light by ASTM D1003-21, while the refractive index falls near 1.565–1.570. Published data for 315NTR’s specific optical and moisture values are limited; these class values should be replaced with certificate data before tooling approval.

In mechanical response, SAN 315NTR is not a rubber-toughened system. The random styrene-acrylonitrile backbone provides higher rigidity than general-purpose polystyrene and better stress-crack resistance against household fats, edible oils, and dilute acids, but the absence of a discrete elastomer phase limits room-temperature impact energy. Class-level tensile stress at yield for general-purpose SAN measured by ISO 527-2:2021 at 50 mm/min lies between 65–75 MPa; flexural modulus by ISO 178:2019 typically falls within 3300–3800 MPa. Charpy notched impact strength at 23 °C by ISO 179-1:2023 is commonly 1.5–2.5 kJ/m², which is approximately one order of magnitude lower than impact-modified ABS. These boundaries make 315NTR suitable for rigid transparent housings, display windows, and consumer appliance parts where load is primarily static or short-term and where impact events do not exceed ordinary handling. The product is not appropriate for highly loaded snap-fits, instrument panels with aggressive airbag deployment, or outdoor uncoated applications requiring UV retention beyond 1000 h of accelerated weathering; published data for 315NTR’s UV performance is limited.

Where does SAN 315NTR fall within the styrene-acrylonitrile copolymer viscosity envelope?

Melt viscosity classification determines whether a transparent SAN can fill a thin-wall part without excessive injection pressure. High-flow SAN grades intended for complex flow paths are commonly characterized at 220 °C with a 10 kg load using ISO 1133-1:2022. The expected melt mass-flow rate for a high-flow natural grade such as 315NTR is typically in the 20–40 g/10 min interval, although the exact 315NTR value must be confirmed from the supplier’s certificate of analysis. By comparison, standard-viscosity SAN 320 may fall closer to 10–20 g/10 min, and very high-flow SAN 330 may exceed 40 g/10 min; these differences shift maximum flow length-to-wall thickness ratios, injection pressure requirements, and screw recovery time. In a thin-wall electronic display window with wall stock below 1.2 mm, a melt flow below 15 g/10 min may require melt temperatures approaching the degradation limit, while a material in the 315NTR flow band permits lower injection pressure and reduced residual stress near the gate. The selection of 315NTR over standard SAN 320 is therefore driven by part geometry, not by a fundamental change in chemical resistance.

Polymer molecular weight distribution also controls melt elasticity and surface aesthetics. Very high-flow SAN may exhibit greater free monomer or oligomer content, leading to plate-out on mould surfaces or increased mould deposit after long runs. Production-scale behaviour for SAN of this flow class is characterized by shear thinning above apparent wall shear rates of 1000 s⁻¹, permitting short injection times, but rapid filling across long flow fronts can generate gate blush or jetting. A mould temperature of 40–80 °C, coupled with a melt temperature of 220–250 °C, is typical for high-flow SAN to maintain gloss and minimize weld-line visibility. The actual melt temperature must remain below the point at which acrylonitrile-containing copolymers begin yellowing; visible decomposition usually produces a yellow shift in the transparent matrix, reducing light transmittance before mechanical failure occurs.

Injection gate geometry, shear heating, and regrind stability

Before the pellets reach a reciprocating screw, the moisture content must be lowered to avoid splay and gate blush. Pre-drying in a desiccant dryer at 80 °C for 2–4 h to a dew point of −20 °C or lower is recommended; moisture above 0.05 % becomes visible as silver streaks on transparent surfaces. The resin is processed on a general-purpose screw with L/D of 20:1 to 24:1 and compression ratio 2:1 to 3:1; a screw designed for GPPS is usually acceptable, whereas a deep-channel PE screw may generate insufficient shearing and poor melt homogeneity. Back pressure of 0.3–0.7 MPa helps homogenize the melt without excessive screw recovery time. Batch-to-batch variation in natural transparent grades requires monitoring of melt viscosity and yellowness index; pellets stored at relative humidity above 60 % should be re-dried before use.

Injection speed profiles are set to minimize flow-front hesitation. The polymer exhibits mould shrinkage of 0.5–0.7 % parallel to flow and 0.6–0.8 % perpendicular to flow, depending on wall thickness and packing pressure. Moulds with polished cavities require consistent packing to avoid sink marks near ribs; the pack pressure is typically 60–80 % of injection pressure. Hot runner systems above 230 °C can initiate discoloration in long residence times, so the hot runner manifold should be equipped with independent zone control and shear-balanced channels. Parts may be annealed at 70–80 °C for 2 h to reduce moulded-in stress, though annealing will not convert the resin into a high-impact material. Regrind of natural transparent SAN can be added at 20–30 % by mass if the material has been dried and free from contamination; higher regrind content increases the risk of optical haze and slight yellowing, particularly in thick sections.

When transparent covers must tolerate detergent, oil, and stack loading, SAN 315NTR is best evaluated against SAN 320, SAN 330, and ABS

In transparent appliance windows, the design choice is rarely SAN 315NTR versus PMMA alone; it is usually SAN 315NTR versus a lower-flow SAN, a very high-flow SAN, or a translucent ABS. The table below uses class-level published values for general-purpose transparent SAN and does not replace lot-specific data for 315NTR. Nevertheless, it identifies the trade-offs that motivate 315NTR selection: intermediate melt flow, a thermal deflection temperature near 94–100 °C at 1.8 MPa, and a light transmittance substantially above ABS. Styrene-acrylonitrile copolymers also exhibit better resistance to household salad oils and dilute sodium hydroxide than GPPS, though prolonged exposure to concentrated solvents is expected to stress-crack the moulding. A stress-crack test using a 0.5 % strain jig and cotton swab immersion in isopropanol or olive oil for 24 h at 23 °C is a practical incoming-lot control; published data for 315NTR under this specific configuration is limited.

The substitution of 315NTR for ABS is usually driven by transparency and rigidity. Opaque ABS provides higher notched impact strength by roughly an order of magnitude, but its flexural modulus is about 40 % lower. In a transparent lid for a food processor, the SAN window must survive static load under a stack of bowls; ABS would resist dropping but would obscure the contents. PMMA provides higher transmittance and surface hardness, but PMMA absorbs more water, may exhibit higher coefficient of linear thermal expansion, and is less resistant to certain kitchen oils; PMMA also has a Vicat softening point often lower than SAN under load. SAN 315NTR therefore occupies the gap between GPPS and PMMA in chemical resistance and between ABS and PMMA in transparency. Grade-specific values for the coefficient of linear thermal expansion, typically 70–80 × 10⁻⁶ K⁻¹ by ISO 11359-2:2021, and the Vicat B50 softening point, typically 104–108 °C by ISO 306:2022, should be taken from the certificate of analysis. Published data for 315NTR’s CTE is limited.

Chemical compatibility must be examined under strain because SAN is susceptible to environmental stress cracking in the presence of certain solvents, esters, and aromatic hydrocarbons. Contact with acetone, methyl ethyl ketone, toluene, or concentrated ethanol can induce crazing at critical strain values below 0.3 % for many SAN grades. Therefore 315NTR must not be used in transparent parts that will be solvent-welded or wiped with aggressive solvent-borne cleaners while under clamp load. Mild detergent solutions, dilute acetic acid, and aliphatic household oils are generally tolerated better than by GPPS, but compatibility testing on the final moulded geometry is required because injection-moulded residual stress can reduce the effective chemical resistance. The absence of a rubber phase also means that the material retains its stiffness in contact with fats, which is relevant for food-processor bowls and cosmetic packaging where GPPS may soften or stress-crack prematurely.

From a regulatory standpoint, SAN 315NTR must be evaluated against the final article. The resin family is generally compliant with RoHS 2011/65/EU Annex II, as no intentionally added lead, cadmium, mercury, hexavalent chromium, PBB, or PBDE are present in natural transparent SAN. REACH obligations under EC 1907/2006 require the downstream user to confirm that residual styrene and acrylonitrile monomer concentrations are below any applicable specific restriction limits; the supplier’s safety data sheet provides classification. Food-contact status is not automatic. In the United States, styrene-acrylonitrile copolymers may fall under 21 CFR 181.32 for certain indirect-contact uses, provided the grade and colorants meet the intended food type and temperature. In the European Union, a specific migration limit for acrylonitrile is set at a non-detectable level with a detection limit of 0.01 mg/kg; laboratory migration testing under the final article geometry is required. Grade-specific approval for 315NTR must be obtained from Kumho Petrochemical before use in food-contact or medical packaging because processing aids, regrind, and colour concentrates can alter the compliance envelope.