EMS-Grivory Grilamid XE 3997 nat is an unreinforced, natural-colour, amorphous polyamide moulding compound based on PAMACM12. The polyamide backbone is formed from bis(4-amino-3-methylcyclohexyl)methane and dodecanedioic acid, yielding a transparent cycloaliphatic polyamide with no significant crystalline melting point. The grade is supplied as a neat, unpigmented resin intended for injection moulding of thin-wall technical, optical, medical, and pharmaceutical contact components. The designation “nat” identifies the natural colour state and is not itself a compliance statement. Representative physical data place the density at 1.01 g/cm³ when measured according to ISO 1183-1, a glass transition temperature of approximately 152 °C under ISO 11357-2, and a melt volume-flow rate of 12 cm³/10 min at 275 °C/5 kg according to ISO 1133-1. The dry-as-moulded tensile modulus is approximately 2200 MPa and the conditioned tensile modulus is approximately 1900 MPa under ISO 527-1/-2.

The amorphous morphology gives the product an optical clarity that semi-crystalline polyamides cannot provide. In processed parts, the absence of spherulitic scattering centres produces low haze and high transmitted-light clarity across wall sections typical of diagnostic housings, fluid-handling manifolds, and pump bodies. The material also has lower mould shrinkage anisotropy than many semi-crystalline grades. Representative shrinkage values fall near 0.8 % longitudinal and 0.9 % transverse under ISO 294-4, which supports predictable tool compensation in multi-cavity moulds. The moisture uptake is moderate for a polyamide: approximately 1.1 % at 23 °C/50 % RH and 3.5 % at saturation in water under ISO 62. These values are lower than those of unreinforced PA6 or PA66, which typically absorb 8.5–9.5 % water at saturation, and the stiffness shift from dry to conditioned states is correspondingly smaller.

Why Does the MACM12 Backbone Produce an Optically Clear Polyamide?

The substituted cyclohexane rings in the MACM diamine disrupt chain packing sufficiently to suppress crystallisation during melt cooling. Under ISO 11357-3, the material does not display a conventional semi-crystalline melting endotherm. The amorphous structure allows light transmission through unoriented and moderately oriented wall sections without the opacification that occurs when spherulites form in PA6 or PA66. This structural difference also changes the mechanical and thermal response under load. The glass transition temperature of around 152 °C produces a heat deflection temperature under 1.80 MPa of approximately 125 °C by ISO 75-1/-2, with a 0.45 MPa HDT/B value near 140 °C and a Vicat B50 softening temperature near 145 °C under ISO 306. These thermal benchmarks are higher than those of typical aliphatic PA12 and PA6 but lower than the deflection temperature of semi-crystalline PA66 under high load. The polymer therefore tolerates short hot-water or steam exposure, but it is not a replacement for high-heat semi-aromatic polyamides or PEEK in continuous high-load thermal environments.

Mechanically, the grade offers a ductile failure mode. Notched Charpy impact strength is reported at approximately 8 kJ/m² dry and 9 kJ/m² conditioned according to ISO 179-1/1eA. The yield stress is approximately 80 MPa dry and 70 MPa conditioned under ISO 527-1/-2, while elongation at yield is near 7 % dry and 8 % conditioned. These values are lower than those of impact-modified polycarbonate and higher than those of unmodified PMMA. The combination of moderate stiffness, high optical clarity, and resistance to aliphatic hydrocarbon and alcohol contact makes the material suitable for transparent covers, flow meters, filter housings, and diagnostic components.

Before injection moulding, the resin must be dried to a residual moisture content below 0.10 %, with moisture level confirmed by Karl Fischer titration according to ISO 15512. Drying in a desiccant-bed or vacuum dryer at 80 °C for 4–8 h is typical. Open hopper exposure at 60 % RH can restore enough surface moisture within 30 min to generate splay and silver streaking on 1.2 mm wall sections. In production-scale moulding of transparent components, silver streak is a common failure mode when the dryer dew point drifts above -20 °C, because dissolved water expands at the flow front and leaves visible surface defects. The material should be processed with a protective nitrogen or dry-air blanket when ambient humidity exceeds 60 % RH.

Injection Moulding Window, Drying Threshold, and Shrinkage Control

Melt temperature measured at the nozzle should be maintained between 250 °C and 280 °C, with the maximum recommended melt temperature near 300 °C. Above that threshold, thermal degradation of the polyamide chain can produce yellowing and reduced melt viscosity. At 270 °C, residence time should not exceed 5 min, especially in hot-runner systems with dead spots or heated sprue bushings. A low- to medium-shear screw with L/D between 18 and 22 and compression ratio from 1.5 to 2.0 is preferred. High-compression screws designed for semi-crystalline PA66 can generate excessive shear heating and cause local overheating of the amorphous melt. Injection units should be sized so the shot volume occupies 30–70 % of barrel capacity to avoid excessive residence time and melt inventory.

Mould temperature is a critical variable for optical parts. The preferred range is 40–80 °C, with 50–60 °C commonly selected for thin-wall diagnostic housings. Uniform mould cooling is necessary because asymmetric temperature fields create orientation gradients and visible birefringence. In multi-cavity tools, cavity-to-cavity melt-filling imbalance can shift shrinkage and create part-to-part variation in transmitted-light clarity. Gates should be positioned to avoid jetting, particularly in transparent parts with polished surfaces. A valve-gate hot runner may be used only if it is naturally balanced and free of stagnation zones; otherwise, cold sprue or edge gates with open nozzles reduce yellowing risk. Production experience with natural transparent polyamide shows that oversized hot-runner manifolds and long heated drops can generate discolouration before any mechanical property loss is measurable.

Moisture-conditioned values refer to specimens conditioned according to ISO 1110. The shift from dry to conditioned modulus reflects plasticisation of the amide network by absorbed water. In service, components that operate in humid environments or intermittent water contact should be evaluated with conditioned values rather than dry-as-moulded data. Dimensional change from water uptake is lower than for PA6 and PA66 but is not zero, and press-fit or snap-fit designs must tolerate small swelling or stress relaxation in water-rich environments.

The grade differs from unreinforced PA6 and PA66 in transparency, moisture uptake, and mould shrinkage behaviour. PA6 and PA66 are semi-crystalline and opaque to translucent, with higher water absorption and greater stiffness loss after conditioning. The amorphous character of PAMACM12 also avoids the pronounced post-shrinkage and anisotropy that can occur in semi-crystalline polyamides. Compared with polycarbonate, the product has lower density, better resistance to stress cracking in many alcohol-based disinfectant and aliphatic hydrocarbon environments, and lower notched impact strength. Polycarbonate remains superior for very high impact applications, but its density near 1.20 g/cm³ is approximately 16 % higher than that of XE 3997 nat. Compared with PMMA, the polyamide has markedly higher ductility and chemical resistance, but PMMA offers higher surface hardness and lower moisture uptake.

Relative to PA12, which is also low-density and low-water-absorbing, the present grade is amorphous and transparent, whereas PA12 is semi-crystalline and generally translucent to opaque. PA12 has a lower glass transition temperature and softens at lower service temperatures, while PAMACM12 retains rigidity to higher temperature because of its cycloaliphatic diamine structure. Relative to other EMS transparent polyamides, XE 3997 nat is positioned as a regulated-documentation natural grade with controlled consistency for medical and pharmaceutical converters. Direct substitution between transparent polyamide grades without revalidation is not recommended because additive packages, MVR, and lot-specific compliance statements may differ.

The comparative values are rounded typical industrial data and are not a substitute for testing on the final component. In particular, water saturation values depend on specimen thickness and conditioning protocol under ISO 62. Published data for highly specific end-use configurations of this grade may be limited, and the supplier should be asked for lot-specific certificates before design freeze.

Chemical-contact behaviour is generally assessed by ISO 175 or ISO 22088 for environmental stress cracking. The polyamide is resistant to many aliphatic hydrocarbons, oils, greases, dilute acids, and alkaline solutions at ambient temperature. It is not recommended for continuous contact with strong oxidising acids, phenols, concentrated formic acid, or chlorinated solvents at elevated temperature because such media can attack the amide linkage or swell the amorphous phase. Alcohol-based disinfectants that are known to stress-crack polycarbonate are less aggressive to this cycloaliphatic polyamide, but the claim must be validated on the final stressed geometry because gate areas, weld lines, and injection-moulded residual stress can concentrate attack.

Steam autoclaving at 121 °C for 20 min approaches the HDT/A of 125 °C. Unstressed parts generally tolerate this cycle, but parts under continuous load or snap-fit deflection may relax because the polymer is near its glass transition. Gamma irradiation at common sterilisation doses may cause slight discolouration, and published data for this specific grade after gamma exposure are limited. For applications requiring post-regulatory assembly, biocompatibility must be evaluated on the final device according to ISO 10993-1. The base polymer may have supplier declarations relevant to food contact or pharmaceutical use, but final-article compliance with EU 10/2011, FDA 21 CFR 177.1500, USP Class VI, RoHS 2011/65/EU, and REACH 1907/2006/EC requires customer-specific verification because colourants, processing aids, and production residues influence the final regulatory status.

The material is unsuitable for continuous load-bearing service above approximately 125 °C under 1.80 MPa because distortion becomes significant. In transparent optical parts with polished surfaces, abrasive contact and aggressive cleaning agents should be screened because polyamide surfaces are softer than PMMA or glass and can show micro-scratching that reduces clarity. Dry-air or vacuum drying, controlled melt residence time, balanced filling, and validation of conditioned mechanical properties are the principal engineering controls for this product.