EMS-Grivory Grilamid® TR 55 LZ is an amorphous, transparent copolyamide based on a PA12/MACMI backbone. The MACMI monomer unit, derived from 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane and isophthalic acid, suppresses chain ordering sufficiently to eliminate spherulitic crystallinity. The resulting single-phase structure permits visible-light transmission while retaining the resistance of polyamide to many aliphatic hydrocarbons, oils and dilute alkaline media. Manufacturer literature lists the unfilled natural grade as having a density of 1.06 g/cm³ to ISO 1183-1, a dry tensile modulus of 2700 MPa at 1 mm/min to ISO 527-1/-2, and a glass transition temperature of 155 °C to ISO 11357-1/-2. The LZ suffix identifies a low-viscosity injection-moulding variant within the TR 55 family, with melt volume-flow rate in the order of 25 cm³/10 min at 275 °C and 5 kg load to ISO 1133-1. The grade is used where dimensional control, optical clarity and chemical resistance are required in thin-walled technical parts, including fluid-handling components, housing windows, medical device components and consumer goods exposed to repeated hygiene cycles.

What structural features distinguish PA12/MACMI from semicrystalline PA12 and PA6?

The absence of a melting endotherm is a defining characteristic. Unlike semicrystalline PA12 homopolymer, which typically shows a glass transition near 42 °C and a crystalline melting peak near 178 °C, Grilamid® TR 55 LZ exhibits no crystalline melting transition in differential scanning calorimetry. The aromatic isophthalic segments and the bulky cyclic MACM diamine restrict chain packing. As a result, the material remains transparent in thick cross-sections, while semicrystalline PA12 and PA6 become translucent or opaque depending on wall thickness, spherulite size and cooling rate. The amorphous structure also reduces anisotropic shrinkage; parts moulded from PA12/MACMI develop more uniform linear shrinkage than fast-crystallizing PA6 or PA66, although absolute shrinkage remains below values typical of acetal or semi-aromatic polyphthalamide grades. Dimensional stability in humid environments is additionally controlled by moisture uptake. The 24 h water absorption at 23 °C is approximately 0.5 % to ISO 62, lower than many standard aliphatic amorphous polyamides but higher than PA12 homopolymer. Saturation water uptake is reported in the range of 5.5 %; therefore design calculations for wet service conditions must account for plasticisation and reversible dimensional growth.

Thermal performance is governed by the glass transition rather than by crystallite melting. Heat deflection temperature under 1.8 MPa load is approximately 130 °C to ISO 75-1/-2, while Vicat softening temperature B/50 is approximately 155 °C to ISO 306. The material retains usable stiffness below the glass transition; above 155 °C, the modulus declines rapidly. Continuous exposure above 120 °C in air may produce oxidative yellowing and surface degradation, and the grade is not recommended for underhood applications where sustained hot air or exhaust gas impingement exceeds that threshold.

Injection Moulding Process Window and Hot-Runner Residence Limits

Before melt processing, the granulate is dried in a dehumidified-air dryer. Recommended drying condition is 80 °C for 4 h to 8 h, with a dew point below −30 °C. Residual moisture measured by Karl Fischer titration should be below 0.10 % by mass. Inadequate drying produces silver streaks and hydrolytic molecular-mass reduction in the melt, with a corresponding loss of impact strength. On production-scale injection machines, barrel temperature profiles are typically set between 240 °C at the feed throat and 280 °C at the nozzle, with melt temperature monitored at 260 °C to 290 °C. Because the LZ designation denotes low melt viscosity, screw recovery is comparatively rapid and back pressure should be limited to 5 MPa to 10 MPa to avoid excessive shear heating. Mould temperature is generally maintained between 40 °C and 80 °C. The lower range is acceptable for simple geometries with generous radii; the upper range improves surface replication and reduces internal stress in polished optical windows. For thin-wall parts below 1.0 mm nominal wall thickness, filling analysis should be performed with the material’s high-flow rheology data, and gate sizes should be increased by 10 % to 20 % relative to PC or PMMA gates to prevent premature freeze-off at the gate land.

Hot-runner systems and heated spruce bushings require close residence-time control. Melt residence time should not exceed 10 min at processing temperature. At 15 min or beyond, visible discoloration and molecular-mass shift can occur, particularly in unvented hot-runner manifolds. Needle-valve systems should be purged with fresh material after any interruption longer than 5 min. In multicavity tools, balance of melt delivery is critical because the amorphous melt exhibits shear-thinning but no crystallisation plateau; cavities fed by longer flow paths may show higher orientation, birefringence and stress-whitening around the gate. Annealing of moulded parts at 80 °C for 2 h is sometimes applied to reduce moulded-in stress before solvent contact or machining, but annealing should be validated because it can reduce transparency slightly in thick regions.

In water-management and medical device production, chemical resistance and sterilisation compatibility are evaluated before lot release. The PA12/MACMI structure provides resistance to hydrolysis in neutral water at temperatures up to 80 °C, and to common aliphatic hydrocarbons, diesel fuel fractions, glycerine and many aliphatic alcohols. Strong mineral acids, halogenated solvents and strongly oxidising cleaning agents should be avoided or tested under stress-free conditions. For fluid-contact applications, the natural grade is often qualified to ISO 10993-5 and ISO 10993-10 for cytotoxicity and irritation; however, colour concentrates, external lubricants and mould-release sprays require separate evaluation because they can alter the biocompatibility profile. For steam autoclave use at 121 °C, the material retains gross dimensions because the cycle temperature remains below the glass transition. Published data for multi-cycle autoclave optical retention is limited; manufacturers and end users typically generate internal qualification data for the specific wall thickness, sterilisation chamber humidity ramp and load configuration. Gamma sterilisation at 25 kGy to 50 kGy may produce slight yellowing, and the colour shift is more visible in natural transparent grades than in tinted or opaque versions.

When comparative selection moves from polycarbonate or PMMA to an amorphous polyamide

Selection of Grilamid® TR 55 LZ instead of bisphenol-A polycarbonate commonly occurs when stress-cracking resistance in alcohols, triphenyl phosphite-free processing, or lower sensitivity to alkaline cleaning agents is required. Polycarbonate provides higher impact strength and higher modulus below 100 °C, but it is vulnerable to stress cracking in isopropanol and certain fatty alcohol ethoxylates used in cleaning wipes. PA12/MACMI offers better resistance in those fluids, although it has lower notched impact strength than polycarbonate and should not be used as a direct drop-in replacement for load-bearing safety parts. Compared with PMMA, the polyamide grade has lower modulus and lower surface hardness, but it avoids brittle failure in snap-fit assemblies and provides better resistance to ester-based greases and aliphatic hydrocarbon media. Dimensional control after moulding is governed by moisture absorption rather than by post-mould crystallisation, so conditioning to equilibrium moisture prior to metrology is necessary; parts machined or inspected in the dry-as-moulded state may show subsequent reversible growth of 0.2 % to 0.5 % when exposed to humid service conditions.

Against other EMS-Grivory transparent polyamides, TR 55 LZ is differentiated from the lower-density Grilamid® TR 90 type by its higher stiffness and lower elongation at break. TR 90 is positioned for flexible transparent components, while TR 55 LZ is applied where greater tensile modulus and reduced creep under sustained load are needed. The difference arises from the specific PA12/MACMI chemistry and the aromatic isophthalic contribution, which stiffens the chain without inducing crystallinity. Final material selection must be confirmed through moulded-part testing because the published datasheet values for dry as-moulded states do not fully represent behaviour after moisture conditioning, sterilisation or long-term exposure to processing oils and pH-adjusted cleaners.