CENTROPLAST CENTROMID 12 LE soft is a plasticised polyamide 12 compound supplied as cylindrical granules for flexible extrusion and injection-moulded components. The LE designation indicates a low-extractable formulation strategy, while the soft grade identifies reduced flexural stiffness and increased elongation compared with unmodified PA12. The base polymer is produced from laurolactam; flexibility is achieved by a proprietary modification system that lowers stiffness without changing the fundamental polyamide 12 backbone. Product-specific values are controlled by the CENTROPLAST technical datasheet and lot certificate. The class-level data presented below represent the typical envelope for plasticised PA12 soft extrusion compounds, not a contractual specification, because public lot-specific data for this exact designation remain limited.

Typical physical parameters for the class include density under ISO 1183-1:2019 between 1.01 g/cm³ and 1.04 g/cm³, Shore D hardness under ISO 868 between 55 and 70, and tensile modulus under ISO 527-2:2012 below 800 MPa. Nominal strain at break is generally above 250%. Unmodified PA12 reference grades exhibit Shore D hardness above 75 and tensile modulus between 1400 MPa and 1800 MPa. The soft grade therefore addresses components that require tight-radius bending, snap-fit insertion, or vibration damping where rigid PA12 would kink or fail by flexural fatigue. Published data for this specific configuration is limited; the manufacturer’s lot certificate remains the controlling reference.

What separates CENTROMID 12 LE soft from unmodified PA12 and PA11 in flexible tubing?

Relative to unmodified PA12, the LE soft grade lowers flexural modulus and Shore D hardness while retaining the low equilibrium moisture uptake of the polyamide 12 backbone. At 23 °C and 50% RH, PA12 typically absorbs less than 1.0% moisture under ISO 62:2008, whereas PA6 and PA66 absorb 2.5% to 3.0% under the same conditions. This lower moisture uptake reduces swelling and dimensional change in humid pneumatic circuits and fuel vapour lines.

Compared with PA11, PA12 offers lower density and lower moisture uptake, but the melting peak determined by differential scanning calorimetry under ISO 11357-3:2018 is slightly lower, commonly in the range 170 °C to 180 °C for PA12 versus 185 °C to 195 °C for PA11. The practical consequence is that PA11 may provide a marginally higher continuous-use temperature, while PA12 soft provides lower mass and better dimensional stability in wet environments. The choice is therefore governed by the upper service temperature and extraction limits of the target assembly.

Flexible PA12 compounds generally retain notched impact at low temperatures. ISO 179-1/1eA values at -30 °C may remain above 10 kJ/m² for plasticised grades, while unplasticised PA12 may drop below 8 kJ/m². For unsupported tube bending, the soft grade is less prone to stress whitening and kinking; however, plasticiser migration over time can increase stiffness at elevated temperatures. Accelerated ageing under ISO 188:2011 at 100 °C for 168 h is commonly used to screen for hardness drift. If hardness increases by more than 5 Shore D points after ageing, the application should be reviewed for plasticiser loss under service conditions.

Migration kinetics are diffusion-controlled and follow Fickian behaviour in thin-walled sections; the diffusion coefficient increases with temperature and with the solubility parameter difference between plasticiser and contact fluid. In fuel contact, the plasticiser can be extracted by aromatic hydrocarbons, increasing hardness and reducing flexibility. Extraction resistance is assessed by immersion under ASTM D471 reference fluids, but exact fluid-specific data for CENTROMID 12 LE soft must be obtained from the manufacturer. The LE designation indicates that the formulation is intended to reduce the total extractable fraction, but it does not eliminate swelling in aggressive solvents.

In corrugated tube and pneumatic line extrusion, the material is dried to a residual moisture content below 0.1% by weight in a desiccant dryer with a dew point of -30 °C or lower. Drying at 80 °C for 4 h to 6 h is typical; drying above 90 °C can cause plasticizer exudation, pellet surface tack, and feed-throat bridging. Processing on a single-screw extruder with a 25:1 to 30:1 L/D barrier screw and screen packs from 60 µm to 120 µm is used on production lines; a gear pump reduces pressure oscillation in thin-wall tube dies.

Melt temperature at the die entry should be maintained between 210 °C and 230 °C. Residence time above 240 °C is minimised because oxidative chain scission and volatile additive loss can shift viscosity and increase extractables. Barrel temperature profiling from 180 °C at the feed throat to 220 °C at the metering section is common. At output rates above 80 kg/h, screw speed reductions or grooved-barrel cooling may be required to control shear heating. Shark-skin surface defects at the die exit indicate excessive shear stress; line speed reduction or die-land modification is preferred over increasing melt temperature. Melt-pressure variation across a 60 µm screen pack should remain below 5 bar; larger pressure swings indicate screen blinding from degraded polymer gels or additive agglomerates.

For injection-moulded fittings and quick-connect bodies, a low-compression screw of 2.5:1 to 3.0:1 with short back pressure is used. Melt temperature of 220 °C to 240 °C, mould temperature 60 °C to 90 °C, and holding pressure 40 MPa to 70 MPa are typical class-level settings. The soft grade fills thin walls at lower injection pressure than unmodified PA12, but gates must be sized for the higher elongation and lower modulus to avoid jetting and flow marks. Vent depths of 0.01 mm to 0.02 mm are used to prevent gas burns without flash.

The main process conflict is between moisture control and plasticizer bleed. Insufficient drying leads to hydrolytic degradation at melt temperatures above 220 °C, visible as viscosity reduction, gas bubbles, and reduced tube burst strength. Overdrying or excessive barrel temperatures can extract the softening additive, producing a harder skin on pellets and increasing Shore D by 5 to 8 points in extruded wall sections. Closed-loop hopper drying with dew-point monitoring and melt-pressure logging is therefore specified for stable production.

During extrusion, molecular orientation in the machine direction increases tensile strength along the tube axis but reduces hoop strength unless the die is designed for balanced drawdown. For PA12 soft tubing, drawdown ratios are typically limited to 1.5:1 to 2.5:1 to preserve hoop strength and elongation. Higher drawdown can produce anisotropic shrinkage and poor fitting retention. In multilayer tube constructions, PA12 soft is often coextruded with EVOH barrier layers or PA6 inner layers; tie-layer selection must account for maleic anhydride grafted polyolefins to maintain interlayer adhesion.

Regrind from sprue, start-up purge, and edge trim can be added at up to 20% in many tube extrusion operations, but the exact ratio must be validated for burst strength and extractables. Multiple heat histories increase gel formation and can raise the extractable fraction. Closed-loop reprocessing of post-industrial scrap is preferred over post-consumer recyclate for applications in pressure-rated tubing. Burst strength validation should follow ISO 1167 or ASTM D1598 on finished tube specimens, not on injection-moulded plaques.

Laser welding of PA12 soft to rigid PA12 is possible where the laser-transparent upper layer and laser-absorbing lower layer have melt-temperature overlap. Because the soft grade contains plasticiser, laser transmission may be reduced by additive haze; transmission at 940 nm should be checked on natural or black specimens. Ultrasonic welding requires amplitude and force adjustment for the lower modulus; high amplitude can melt the soft surface before the joint interface is heated. Adhesive bonding may require surface pretreatment by plasma or corona because the low surface energy of PA12 can limit bond strength; lap-shear testing under ISO 4587 is used to compare adhesive systems.

After injection moulding, PA parts are often conditioned to equilibrium moisture to increase impact toughness. For PA12 soft, conditioning is less critical than for PA6 or PA66 because moisture uptake is low; however, if parts are conditioned at 70 °C and 62% RH, dimensions may increase by 0.1% to 0.3%. Dimensional tolerances should be validated after conditioning to the expected service humidity. Mould shrinkage for soft PA12 grades is generally in the range 0.5% to 1.0% depending on wall thickness and gate orientation, measured after 24 h at 23 °C. Post-mould shrinkage at elevated temperature may add 0.2% to 0.5%. Packing pressure should be held until gate freeze; gate freeze time is typically longer than for unmodified PA12 because the lower modulus delays solidification under pressure.

When PA12 LE soft is evaluated against polyether block amide and TPU in flexible conduit applications

In comparison with polyether block amide, plasticised PA12 soft generally retains higher polyamide chemical resistance and lower moisture uptake, but polyether block amide provides greater elastic recovery and lower tensile set after repeated elongation. The choice in flexible conduit and cable protection therefore depends on whether chemical exposure or cyclic flexural deformation is the limiting requirement. For oily environments with repeated bending, PA12 soft may be preferred; for high elastic recovery at high strain, polyether block amide grades are typically specified.

Compared with thermoplastic polyurethane, PA12 soft exhibits lower density by roughly 0.15 g/cm³ to 0.20 g/cm³ and better resistance to hydrolysis in hot-wet environments, but thermoplastic polyurethane offers higher abrasion resistance and tear strength. Abrasion resistance should be quantified under ISO 4649 or ISO 5470-1; published class-level comparison data for this exact PA12 soft grade remain limited. For cable sheathing, flexibility at low temperature and chemical resistance may outweigh abrasion; for pneumatic hose liners, thermoplastic polyurethane may be used as an outer jacket over a PA12 soft inner layer.

Low-extractable behaviour is relevant for fuel vapour tubing, pneumatic lines, and air-conditioning hose connectors. Extractable-matter testing under ISO 6427:2013 is used to measure organic extractables after solvent exposure. For fuel-contact applications, the material is often evaluated against SAE J2260 for non-metallic fuel system tubing or SAE J844 for air brake tubing. When these standards are invoked, the finished tube assembly must be tested rather than the raw compound alone, because extrusion orientation, heat history, and fitting insertion modify burst strength and permeation behaviour.

Unopened bags should be stored in dry conditions below 30 °C and protected from direct sunlight. If bags are opened in high-humidity environments above 60% RH, the material should be re-dried before processing. Moisture regain in plasticised PA12 can be more rapid than in unmodified PA12 because the plasticiser can increase free volume; hopper residence time at high humidity should therefore be limited. A desiccant-bed dryer with -40 °C dew point is preferred over hot-air ovens, which may cause surface oxidation of granules during prolonged drying.

For cable sheathing, volume resistivity and dielectric strength may be relevant. PA12 soft grades typically show volume resistivity above 10^12 Ω·cm after conditioning at 23 °C and 50% RH, measured under IEC 62631-3-1. This value is humidity-dependent; immersion reduces resistivity. The soft grade may be formulated with carbon black for UV protection, which affects surface resistivity and cannot be assumed insulating unless specified.

Long-term thermal ageing of PA12 soft is limited by oxidative degradation and plasticizer volatilisation. Continuous-use temperatures above 90 °C may increase hardness and reduce elongation after several thousand hours. Thermal endurance testing under ISO 2578 or IEC 60216 is required to establish a temperature index for a specific property endpoint. Published data for this exact CENTROMID 12 LE soft configuration is limited; therefore, service-temperature claims should be derived from lot-specific ageing studies, not from generic PA12 thermal data.

Regulatory compliance and extractables testing

The base PA12 chemistry may be evaluated under FDA 21 CFR 177.1500 for food-contact use and EU 10/2011 for plastic food-contact materials. Such compliance is concentration- and migration-limited and must be confirmed for the specific CENTROMID 12 LE soft formulation and the final article geometry. For medical device components, cytotoxicity testing under ISO 10993-5 and sensitisation or irritation testing under ISO 10993-10 may be required; the manufacturer should provide a statement of compliance for the exact lot.

Chemical resistance should be assessed under ISO 175:2010 or ASTM D543 with the actual process fluid at the maximum service temperature. Swelling beyond 3% mass uptake or 2% dimensional change is generally considered a risk for load-bearing components, though specific limits depend on design tolerance. Flammability is typically assessed under UL 94; unmodified PA12 is usually classed HB, and a soft grade is unlikely to achieve higher ratings without flame-retardant modification. For applications requiring V-2 or better, a specifically flame-retarded PA12 grade should be selected, not the LE soft general-purpose material.