Shandong Guangyin PA 1212 nylon resin is a long-chain semicrystalline polyamide produced by polycondensation of dodecanedioic acid and 1,12-diaminododecane. The structural repeat unit contains 22 methylene units per 2 amide linkages, yielding roughly 11 methylene units per amide group; this methylene-to-amide ratio is the primary molecular factor behind the material’s lower equilibrium moisture uptake relative to PA 66 and PA 6, whose repeat units contain 6 and 5 methylene units per amide group, respectively. The resin is supplied in pellet form for injection moulding, profile extrusion, and monofilament spinning. The ISO 1043-1 designation is PA1212. Density is determined by ISO 1183-1:2019, tensile mechanical properties by ISO 527-1/-2:2012, and melt volume-flow rate by ISO 1133-1:2022. Equilibrium moisture uptake at 23 °C/50 % RH lies below the values typical of short-chain aliphatic polyamides, which reduces the dry-as-moulded to service-humidified shift in flexural modulus. Because the resin remains semicrystalline, mould shrinkage is anisotropic; published processing data for long-chain polyamides indicate flow-direction shrinkage and transverse shrinkage can differ by a factor of 1.3–1.8 depending on mould temperature, wall thickness, and glass-fibre orientation.

How Does PA 1212 Compare with PA 12, PA 11, and PA 66 in Moisture Uptake and Mechanical Stability?

The performance boundary between PA1212 and standard engineering polyamides is governed less by a single property than by the combined effect of lower amide density, even monomer carbon lengths, and crystallisation behaviour. PA 66 offers higher dry tensile strength and heat deflection temperature because its higher amide density creates a denser hydrogen-bonded network. However, that same network is susceptible to plasticization by absorbed water. In conditioned service at 23 °C and 50 % RH, published comparisons show PA 66 can retain only 55–65 % of dry tensile modulus, whereas long-chain polyamides of the PA 1212 class typically retain 85–90 %. PA 12, produced from laurolactam, has the same approximate 11 methylene units per amide group, and therefore similar moisture uptake, but its odd monomer carbon count and ring-opening synthesis route produce different terminal-group distributions and crystallisation half-times. PA 11, sourced from castor oil, contains 10 methylene units per amide group and is closer in moisture behaviour to PA 1212 than to PA 66, though its melting point is slightly higher and its renewable carbon content is often higher. The table below summarises typical dry-as-moulded ranges for unreinforced grades. The values are drawn from published ISO-based technical literature for long-chain polyamides, not from a specific Shandong Guangyin certificate of analysis; lot-specific values must be obtained from the supplier.

Unlike PA 12, which is typically available as a ring-opened laurolactam polymer with a single amide per repeat unit, PA 1212 is built from two linear monomers and therefore has a different terminal-group distribution and broader molecular-weight architecture. This can alter the response to chain extenders and re-extrusion heat history. Compared with PA 610 and PA 612, PA1212 has a lower amide density and therefore lower moisture uptake; PA 612 has 6 methylene units adjacent to the diamine segment and 10 methylene units adjacent to the diacid segment, giving higher hydrophilicity than PA1212. Compared with PA 1010, the extra two methylene units in the diacid segment of PA1212 further reduce moisture affinity but may reduce tensile stiffness by a small increment.

Injection Moulding and Extrusion Processing Boundaries

For unreinforced PA1212, barrel temperature settings must remain below the onset of thermal oxidation while being high enough to prevent spherulitic freezing in thin walls. A co-rotating twin-screw compounding extruder with 40:1 L/D and a vacuum vent below −0.08 MPa gauge has been described for glass-fibre reinforced variants; unreinforced material can be processed on a shorter 28:1 L/D three-zone screw if melt temperature is kept within 245–275 °C. Screw speed in production-scale extrusion is typically 200–300 rpm; higher speeds increase melt temperature by viscous dissipation and accelerate yellowing if residence time exceeds 8 min. Die head pressure for strand pelletizing is generally 3.0–5.0 MPa. In injection moulding, the processing window is relatively flat, but mould temperature controls the crystalline skin layer and therefore determines the degree of post-mould shrinkage. Mould temperatures below 40 °C produce lower crystallinity and higher subsequent shrinkage, while mould temperatures above 90 °C slow ejection and can increase cycle time. The following parameters are common starting points for unreinforced grades; adjustments are required for glass-fibre reinforced or impact-modified formulations.

On a 75-tonne injection moulding machine with a 40 mm diameter general-purpose screw and a compression ratio of 2.2:1, cushion stability below ±0.5 mm has been observed in production when the non-return valve is free-flowing and the screw tip is free of degraded polyamide deposits. Cushion variation above 1.5 mm is associated with non-return valve leakage and produces short shots in thin-walled connectors with wall sections below 1.0 mm. Batch-to-batch viscosity variation for long-chain polyamides of this class is typically specified as a relative viscosity window of ±0.05 dL/g when measured in 96 % sulphuric acid according to ISO 307:2019; close control of this value is necessary for monofilament spinning because viscosity shifts of 0.1 dL/g can alter draw ratio and filament denier at constant haul-off speed.

Polyamide 1212 is resistant to aliphatic hydrocarbons, diesel, biodiesel blends, engine oil, and zinc chloride salt solutions at ambient temperature. The long aliphatic segment reduces the number of hydrogen-bonding sites available for hydrolysis, but the amide linkage remains vulnerable to strong mineral acids, concentrated phenol, and hot aqueous solutions above 80 °C at pH below 2 or above 12. In circulating hot diesel rigs using 20 % biodiesel at 80 °C for 1,000 h, tensile strength retention above 80 % is reported only if the formulation contains a hindered phenolic antioxidant and no unreacted amine-based processing additive; benzyl alcohol and some fatty acid amide slip agents can plasticize the surface and reduce weld line strength. Published data for this specific configuration is limited to bench-scale immersion testing and cannot replace full vehicle validation.

Glass-Fibre Reinforcement Alters Shrinkage Anisotropy and Melt Viscosity

When 30 wt% short glass fibre is compounded into PA1212 on a 40:1 L/D co-rotating twin-screw extruder with side feeding at 250 °C, melt pressure at the die face typically increases from 3.0 MPa to 4.5–5.5 MPa at constant screw speed, and melt volume-flow rate drops by 30–50 % relative to the unfilled resin. Fibre orientation in the flow direction reduces flow-direction mould shrinkage to 0.4–0.8 %, but transverse shrinkage remains at 0.9–1.2 %, creating warpage in flat parts with asymmetric gate locations. Weld-line tensile strength in glass-filled PA1212 is typically 60–70 % of the non-weld value measured by ISO 527-1/-2:2012; holding pressure at the far end of the cavity and melt temperature near 275 °C improve weld-line recovery more than increasing injection speed alone.

Crystallisation half-times for PA1212 measured by differential scanning calorimetry under ISO 11357-7:2022 are intermediate between nylon 66 and polypropylene, which gives a wider processing window than PA66 for semicrystalline solidification. However, spherulite size and the thickness of the highly oriented skin layer are sensitive to mould temperature; at mould temperatures below 50 °C, the skin layer can exceed 200 µm in parts thicker than 3 mm, producing surface gloss differences and internal stress that is not detected by simple hardness testing. This property difference relative to PA 6 is a processing consideration in aesthetic components.

At shear rates typical of injection moulding, 1,000–10,000 s⁻¹, the viscosity of unreinforced PA1212 follows shear-thinning behaviour with a power-law index of 0.65–0.75 when measured by capillary rheometry at 250 °C. This is lower than polypropylene but similar to PA12. The pressure dependence of viscosity is moderate; increasing melt pressure from 10 MPa to 50 MPa raises apparent viscosity by less than 20 %, which is relevant in long flow-length parts where hydraulic pressure settings are used to infer cavity pressure.

When Low-Temperature Impact and Fuel Resistance Are Simultaneously Required

In flexible fuel-line connectors and pneumatic tubing, the material must maintain sub-zero ductility while resisting aliphatic hydrocarbon swell. Unmodified PA1212 exhibits notched Charpy impact values at −40 °C in the range of 4–8 kJ/m² when measured by ISO 179-1/1eA:2010, depending on molecular weight and moisture condition. Impact-modified grades shift this value upward, but excessive impact modifier loading above 15 wt% reduces fuel resistance and increases volume swell after immersion in FAM B reference fuel. In ISO 175:2010 immersion at 23 °C for 168 h, unreinforced PA1212 typically shows volume swell below 1.5 %, whereas swollen PA 66 can exhibit higher dimensional change and greater stress-crack sensitivity at weld lines. The selection of a high-molecular-weight extrusion grade, with an MVR below 10 cm³/10 min at 230 °C/2.16 kg, is preferred for corrugated tubing because parison melt strength and die swell are more uniform.

For low-temperature impact below −40 °C, the use of a nucleating agent can refine spherulite size and improve consistency, but excessive nucleation lowers melt flow and can increase gate blush in injection moulded parts. In fuel quick connectors moulded from PA1212, post-moulding moisture uptake is slower than in PA 66, which means that property stabilisation after moulding may require conditioning at 23 °C/50 % RH for 72–96 h before dimensional inspection. Accelerated conditioning in 70 °C water for 2 h is not recommended for dimensionally critical parts because the crystalline skin reorganisation differs from gradual humid ageing.

REACH registration under Regulation (EC) No 1907/2006 and RoHS compliance under Directive 2011/65/EU, Annex II, should be documented at the raw-material level. Food-contact suitability is not an inherent property of all PA1212 grades; only specific formulations that are pre-compounded with suitable stabilisers and tested under 21 CFR 177.1500 or EU 10/2011 migration protocols can be used for food-contact engineering applications. Electrical insulation grades require low ionic contamination; surface resistivity measured by IEC 62631-3-2 at 500 V is typically above 10¹³ Ω for conditioned specimens, but the value falls by one to two orders of magnitude after equilibrating at 90 % RH. For potable water contact, test reports to NSF/ANSI 61 or equivalent national standards are not automatically available and must be requested for the exact filled or unfilled formulation.

In continuous air ageing at 120 °C for 500 h, unmodified PA1212 typically retains 70–80 % of tensile strength when an effective copper-based heat stabiliser is present; without copper halide stabiliser, retention falls below 50 %. This is a limitation in underhood applications where peak temperatures exceed 150 °C even briefly. HDT values should not be used as continuous-use temperature ratings.