CENTROPLAST CENTROMID 12 soft is a flexible polyamide 12 (PA12) grade whose product code identifies the base polymer family and the soft modification. The base resin is classified under ISO 1043-1 as PA12; the soft suffix distinguishes this grade from unmodified CENTROMID 12. The material is supplied in cylindrical granules and is intended for extrusion and injection moulding. This grade is specified when a component requires the aliphatic hydrocarbon resistance and low water absorption of PA12 but cannot tolerate the flexural stiffness of standard PA12. The manufacturer has not published the exact plasticization route; therefore the grade can be treated as an externally plasticized or internally flexibilized system. Lot-level mechanical values are reported on the certificate of analysis and should be used for tooling calculations.

The primary mechanical difference between unmodified PA12 and CENTROMID 12 soft is bending stiffness. A standard dry PA12 may show a tensile modulus near 1300 MPa under ISO 527-2, whereas the flexible PA12 class lies in the 200 MPa to 500 MPa range. The reduction in modulus is accompanied by increased creep under continuous load and by lower Shore D hardness. In snap-fit or press-fit designs, the lower modulus reduces insertion force but increases the risk of permanent deformation at elevated temperature. Design calculations should therefore use creep modulus data obtained under ISO 899-1 at the maximum service temperature, not initial tensile modulus.

Mechanical and Thermal Specification Set

Where flexible PA12 mechanical data are generated, the specimens are usually conditioned at 23 °C and 50 % RH and tested according to ISO 527-2 type 1A geometry. The values in the following table are class-level ranges for plasticized PA12 grades, not a guaranteed specification for the CENTROMID 12 soft lot. The manufacturer’s datasheet should be requested for minimum or maximum acceptance limits.

These figures should not be used for safety-critical component validation. The soft grade may show lower melting peak and lower heat deflection temperature than a glass-filled or impact-modified PA12. Under ISO 75-2 at 1.8 MPa, flexible PA12 can fall between 45 °C and 55 °C; published data for this specific configuration is limited.

What Happens When Moisture Ingress Exceeds 0.1 % Before Melt Processing?

Moisture is the main process variable for soft PA12. The material is hygroscopic, and melt-phase hydrolysis reduces molecular weight if the residual moisture is too high. Drying in a desiccant dryer at 80 °C for 4 h to 6 h is typical for the flexible PA12 class. The drying air must have a dew point no higher than -30 °C and the hopper must be sealed when ambient relative humidity exceeds 60 %. Moisture should be verified with a coulometric Karl Fischer method following ISO 15512. If the granule moisture is above 0.10 %, surface splay, die-head bubble formation, and loss of tensile elongation may occur. Above 0.20 %, the melt becomes visibly foamy and the extrudate may show internal voids that cannot be removed by downstream calibration.

On a single-screw extruder with a smooth-bore barrel and screw L/D ratio between 24:1 and 30:1, a reverse-taper screw with constant compression is usually selected for soft PA12. Barrel temperatures are normally set from 220 °C at the feed throat to 250 °C at the die; the adapter and head are held between 240 °C and 260 °C. Screw speeds above 80 min⁻¹ may raise melt temperature above 260 °C through shear heating. At these temperatures plasticizer loss, yellowing, and die-lip deposit formation increase sharply. In injection moulding, the material class is processed at a melt temperature of 230 °C to 250 °C and a mould temperature of 40 °C to 80 °C. Decompression should be kept between 3 mm and 5 mm, and cushion below 8 mm, to limit residence time and discolouration. The following parameters are class-level starting points; the CENTROMID 12 soft datasheet may specify narrower limits for a particular additive package.

In production-scale extrusion of small-diameter tubing, melt-temperature fluctuation of more than ±5 °C can produce measurable wall-thickness variation. A pressure-controlled melt pump between the screw and die helps hold wall thickness to ±0.05 mm on nominal 8 mm tube. However, published data for CENTROMID 12 soft in this specific die configuration is limited, and the machine must be validated with the actual die land length and draw-down ratio.

In practice, the most common extrusion defect with soft PA12 is not bubble formation but die-lip deposit accumulation. The lower molecular weight plasticizer can volatilize at the die exit and condense on the lip. If the die head is held above 260 °C for extended periods, the deposit hardens and disrupts the outer surface of the tube. A brass or steel lip with chromium plating reduces adhesion, and corrective action usually involves reducing head temperature by 5 °C to 10 °C while maintaining melt pressure.

Granule handling before processing also affects lot-to-lot consistency. If bags are opened in a high-humidity environment and not re-dried, the material can pick up surface moisture within 24 h. This surface moisture is not detected by a total moisture method alone; a Karl Fischer oven with controlled temperature is preferred. Batch-to-batch variance in soft PA12 is often due to differences in plasticizer content rather than base polymer molecular weight. A loss-on-ignition or extraction check under ISO 6427 can be used to screen incoming lots if the plasticizer is extractable. The manufacturer’s certificate should state the actual melt volume-flow rate and tensile modulus for the lot.

When Soft PA12 Replaces Unmodified PA12 in Dynamic Seals and Tubing

The soft grade is typically used in seals, bellows, cable sheathing, and flexible pneumatic tubing where bending fatigue and fold cracking are dominant failure modes. Under repeated flexing, standard PA12 may fail if the outer fibre strain exceeds the yield strain. The lower flexural modulus of soft PA12, in the 150 MPa to 400 MPa class range under ISO 178, reduces stress concentration at fold roots and permits smaller bend radii. Because PA12 absorbs only 1.5 % to 2.0 % water at saturation under ISO 62, the dimensional shift in humid service is smaller than with PA6 or PA66. This property is relevant for pneumatic controls where humidity changes must not alter tube diameter significantly.

The trade-off is thermal and creep performance. A soft PA12 part under continuous load will creep more than unmodified PA12 and will exhibit lower heat deflection temperature. In dynamic seal applications, the maximum continuous service temperature is typically below 80 °C in air; above this, plasticizer loss and creep accelerate. In hot water or glycol-containing fluids, the service temperature should be lower because polar fluids can extract monomeric plasticizers. Long-term heat ageing should be evaluated under ISO 188 at the intended service temperature, and extraction should be assessed under ISO 6427 if the part contacts solvents.

The product is also used in cable jacketing where a cold bend test is specified at -25 °C or -40 °C. The flexible PA12 class generally retains impact toughness at these temperatures if the specimen is dry and free of surface defects. Natural, non-stabilized grades will embrittle under prolonged UV exposure; carbon black or a UV stabilizer package is required for outdoor use. Testing for sunlight resistance is commonly performed under ISO 4892-2 or ISO 4892-3. Published data for CENTROMID 12 soft after 1000 h of xenon arc exposure is limited.

Compared with standard CENTROMID 12, this grade lowers insertion force in connectors and reduces the tendency of thin sections to crack in cold environments. Compared with a flexible PA11, the PA12 soft grade has a similar low-water uptake profile, but lower melting peak and generally better resistance to zinc chloride stress cracking. Compared with a thermoplastic polyurethane, the polyamide 12 soft grade has lower density and better aliphatic hydrocarbon resistance, but lower abrasion resistance and less elastic recovery after large deformations. Compared with flexible PA6 or PA66, the PA12 backbone reduces moisture-related mechanical property shift. No single table of hardness values can replace end-use testing; component approval requires the relevant application standard, such as ISO 10993-5 for medical device cytotoxicity or FDA 21 CFR 177.1500 for food-contact polyamide when migration testing is completed.

In multi-layer fuel lines, the grade may be used as a flexible outer or inner layer in combination with an EVOH barrier. The low hardness allows denser routing and reduces connector stress, but the soft PA12 layer increases vapour permeation compared with standard PA12 because plasticizer increases free volume. Therefore a barrier layer is required for fuel vapour control. In pneumatic brake line configurations, the material must be tested under impulse pressure cycles and hydraulic fluids; published data for this specific configuration is limited, and the manufacturer’s fluid resistance list should be consulted. The product is not recommended for continuous exposure to strong acids, strong oxidizing agents, or hot polar solvents. Contact with certain amine-based additives can cause stress cracking or accelerate plasticizer extraction.

In electrical connector applications, unreinforced PA12 often provides a comparative tracking index near 600 V under IEC 60112, but the plasticizer in a soft PA12 can reduce the CTI value. Volume resistivity is generally above 10¹² Ω·cm when dry under IEC 62631-3-1, but moisture and polar plasticizers can lower it. These electrical properties must be measured on the final part at the relevant conditioning state. The material is not a substitute for crosslinked thermosets where dimensional stability at soldering temperatures is required. Soft PA12 can be bonded to itself or to a harder PA12 substrate, but surface treatment and the presence of external plasticizer can alter adhesion. Bond assemblies should be tested under ISO 527-2 or the relevant adhesive shear standard at maximum service temperature.

Certain additives may alter the product. Combination with amine-based heat stabilizers can result in premature yellowing, and certain phenolic antioxidants may be less effective in a plasticized system. The product should not be blended with glass fibre without validating the plasticizer distribution, because high-shear compounding of soft PA12 with glass fibre can increase melt viscosity and cause screw torque overload on extruders with L/D ratios below 32:1. The use of a coupling agent may be necessary for glass-filled soft PA12, but published data for this specific grade is limited.

During continuous hot-air exposure, plasticized PA12 may lose elongation before tensile strength changes. This is a typical failure pattern for externally plasticized systems. Testing under ISO 188 at 100 °C for 500 h can show embrittlement if the plasticizer is volatile or if oxidative degradation dominates. A retention of 50 % of initial elongation is sometimes used as an acceptance criterion; however, the exact limit for CENTROMID 12 soft must be selected from the manufacturer’s thermal ageing data. Published data for this specific configuration is limited.