Supplied as a grey monofilament for fused filament fabrication (FFF), the product identified as Clariant Polyethylene Terephthalate Glycol Grey 3D Printer Filament is a glycol-modified copolyester feedstock. The descriptor combines polymer type, glycol modification, pigment package, and end-use geometry; no additional alphanumeric Clariant grade code is authenticated in the present source, and the spool label must be checked for lot number, nominal diameter, and manufacturing date. The material is a PETG in which cyclohexanedimethanol partially replaces ethylene glycol in the backbone, suppressing quiescent crystallisation, widening the processing window, and reducing the shrinkage-driven delamination seen with unmodified polyethylene terephthalate. Class-typical unfilled PETG densities are 1.23–1.27 g/cm³ under ISO 1183-1, and filament-grade melt mass-flow rates at 230 °C/2.16 kg are commonly between 6 g/10 min and 15 g/10 min under ISO 1133-1:2022. Published data for the exact grey Clariant formulation is limited; values cited here are class-typical unless a lot-specific certificate is identified. In service, the product is used for functional prototypes, manufacturing aids, fixtures, and light-duty housings where the load remains below the tensile yield range of 45–50 MPa and the service temperature does not continuously approach the 70–75 °C heat deflection temperature range under ISO 75-2/B.

Why does glycol modification alter warp stress and layer fusion in FFF?

Unmodified polyethylene terephthalate crystallises on cooling and forms a semi-crystalline network with higher density than the molten state. That phase change generates volumetric shrinkage and residual stress in printed parts, especially when the build platform is maintained near 70 °C or below. PETG reduces crystallisation rate and crystalline content; the material remains predominantly amorphous and therefore has a lower differential shrinkage between the first and last deposited layers. The practical result is reduced edge lifting against polyetherimide or glass build plates. However, the same low crystallinity also reduces high-temperature creep resistance relative to semi-crystalline PET.

On open-frame FFF machines, the recommended bed temperature for PETG is 70 ± 5 °C. A heated chamber above 60 °C improves layer fusion but is not mandatory for parts with wall thickness below 6 mm. First-layer adhesion is typically achieved on a polyetherimide sheet, textured glass, or a coated build plate; bare glass without adhesive can fail because low-crystallinity PETG does not shrink sufficiently to lock onto the surface, and surface contamination lowers the wetting envelope. The first layer should be extruded with a height of 0.15–0.25 mm and a speed not exceeding 30 mm/s; positive squish maintains nozzle-to-bed contact, but excessive squish raises extrusion backpressure and can strip filament at the drive gear. A differential scanning calorimetry scan at 10 K/min under ISO 11357-2 normally shows a glass transition between 75 °C and 80 °C and no significant melting endotherm for fully amorphous PETG. Interlayer fusion requires the new bead to maintain an interface temperature above the glass transition temperature long enough for polymer chain diffusion. With a 0.4 mm nozzle, a layer height of 0.2 mm, and a print speed of 40–60 mm/s, the interface can cool below T_g within seconds; bed temperature and chamber conditions therefore directly control through-thickness tensile strength.

When ambient relative humidity exceeds 60%, PETG spools absorb moisture at the filament surface and along the wound length. The absorbed water is not a plasticiser at room temperature; it becomes a hydrolytic agent at processing temperatures between 230 °C and 260 °C. Ester linkages are cleaved, molecular weight is reduced, and printed parts lose tensile elongation. The failure mode is often visible as excessive fine stringing, a sporadic popping sound at the nozzle, or a reduction in melt strength that produces inconsistent road width. A desiccant dryer or forced-air oven at 65 ± 5 °C for 4–6 h is typical for spooled PETG, with a target residual moisture below 0.03 wt%. Dryer air should be maintained at a dew point of ≤ −40 °C if the spool is to be processed over multiple shifts. Hydrolytically degraded feedstock cannot be fully restored by re-drying; if a spool has been exposed to high humidity for extended periods, molecular weight loss may be irreversible and the material should be sampled for melt flow rate before use.

Filament Diameter, Ovality, and the Melt Pressure Window

Two nominal diameters dominate the FFF filament market: 1.75 ± 0.05 mm and 2.85 ± 0.05 mm. The product may be supplied in either diameter; the exact nominal dimension appears on the spool label and must match the printer’s filament path and firmware settings. A 1.75 mm filament has a higher surface-to-volume ratio, melts more rapidly in a short liquefier, and requires lower drive force; a 2.85 mm filament is preferred for high-extrusion-rate nozzles above 0.6 mm where feed stiffness reduces buckling. Ovality, the difference between maximum and minimum cross-sectional diameter, should be kept below 0.05 mm. Higher ovality creates cyclic variation in melt pressure at the nozzle, often observed as visible pulses in the extrudate or as repeating light and dark bands on the part surface. The melt mass-flow rate of the grey product must be taken from the supplier certificate. For class-typical unfilled PETG, a melt flow rate below 5 g/10 min at 230 °C/2.16 kg may require raising the nozzle temperature by 5–10 °C, while values above 15 g/10 min are more likely to sag on overhangs and form strings unless retraction and cooling are tuned.

During filament production, compounding of the grey pigment masterbatch is typically performed on a co-rotating twin-screw extruder with L/D 40:1 or greater to achieve dispersive and distributive mixing without exceeding 280 °C melt temperature. Filament extrusion then follows on a single-screw extruder with L/D 24:1–30:1, closed-loop diameter control, and water or air cooling. The pigment package in the grey product can increase melt viscosity and barrel pressure by 5–10% relative to natural PETG; this is a qualitative production-scale effect and must be confirmed by capillary rheometry or melt flow rate on the finished material. Incoming quality control should record filament diameter at 3 points per meter and check spool winding tension because tightly wound inner layers can compress the filament and introduce ovality that does not appear on the outer spool surface.

Values from injection-moulded or filament-derived coupons under ISO 527-2 or ASTM D638-14 are not interchangeable with FFF part allowables. Printed part strength depends on raster orientation, interlayer void volume, thermal history, and porosity; Z-direction tensile fracture energy is frequently lower than XY-direction values.

When the grey pigment package is compounded, what changes in drying, flow, and appearance?

The grey colorant package is not an inert diluent; it can alter drying behaviour, melt viscosity, and surface appearance. Carbon black, titanium dioxide, and organic or inorganic toners used to produce grey can nucleate or inhibit crystallisation depending on surface chemistry, and can raise melt viscosity by a few percent. The printing process should therefore be calibrated with the grey spool rather than with a natural PETG profile. Bed temperature, nozzle temperature, and retraction settings should be reconfirmed when switching from natural to pigmented material. The grey grade may also change the visibility of surface defects such as voids, weld lines, or layer-pause artifacts; first-article inspection under diffused light is recommended.

Because some grey pigment components are hygroscopic, the spool surface may exhibit higher moisture uptake than an unpigmented grade. Pre-drying before first use and storage in a sealed bag with desiccant are therefore required. A drying time of 4–6 h at 65 °C remains the starting point, but if the spool has been stored at relative humidity above 60%, the moisture content may require 8 h or more to fall below 0.03 wt%. The exact drying curve should be generated with a moisture analyser; a single-point drying time is insufficient for a lot with unknown storage history. Do not dry PETG at temperatures above 70 °C unless the spool core is monitored, because softening and interlayer welding of the filament wraps can occur before the core reaches equilibrium.

For a 0.4 mm nozzle and volumetric speed between 4 mm³/s and 8 mm³/s, a nozzle temperature of 235–255 °C usually balances melt strength and shear viscosity. Above 270 °C, thermal degradation of PETG may begin to generate acetaldehyde and reduce mechanical strength, even if the melt appears to flow easily. The nozzle should not be held at high temperature for extended periods without extrusion because residence time distribution in the hot end determines the extent of thermal degradation. Retraction distances between 1 mm and 3 mm at speeds of 25–40 mm/s are common for direct-drive extruders; bowden systems may require longer distances, but excessive retraction can draw air into the melt chamber and generate surface defects. Layer fan speed is typically set to 20–50% after the first layer to improve overhang definition; excessive fan output can chill the interface and lower interlayer fracture toughness.

This grey PETG does not require a styrene purge or active carbon filtration common to ABS and ASA printing environments. It also does not exhibit the pronounced crystallisation exotherm of unmodified PET during cooling, which is why printing speeds can be moderate without a heated chamber. However, the same amorphous character means the printed part cannot be crystallised later for improved solvent resistance.

RoHS, REACH, and food-contact limitations must be verified against the supplier certificate

The grey PETG filament can be expected to comply with Directive 2011/65/EU Annex II restrictions for lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers in homogeneous materials. The exact statement appears in the supplier safety data sheet or certificate; the presence of a grey pigment package requires confirmation that the pigment and carrier do not introduce restricted substances above the maximum concentration values. Under Regulation (EC) No 1907/2006, the supplier is obligated to communicate whether any substance of very high concern appears on the Candidate List above 0.1 wt%. For food-contact use, no assumption may be made from the PETG base resin; the grey colorant package, stabilisers, and processing aids must be evaluated under FDA 21 CFR or EU Regulation (EU) No 10/2011 for the intended final article. Printed parts are not inherently food-contact safe because layer lines, surface porosity, contamination retention, and cleaning issues create additional compliance boundaries.

For printed fixtures and machine guards, chemical service boundaries are relevant. PETG has useful resistance to dilute acids, alcohols, and many oils, but it is attacked by ketones, chlorinated hydrocarbons, and strongly alkaline media. The amorphous structure is more prone than semi-crystalline PET to environmental stress cracking in the presence of some solvents. Continuous service at temperatures above 70 °C is not recommended because the material approaches its heat deflection temperature range and may creep under load. Outdoor exposure of grey PETG is possible, but ultraviolet and moisture ageing will shift surface properties over time; the grey pigment may provide some surface UV screening, but no weathering claim can be made without supplier data or accelerated exposure under ISO 4892-2. Storage should be in a sealed bag with desiccant below 30 °C, away from ultraviolet sources and moisture condensation.