PETG is a widely used material in 3D printing, valued for its balance of strength, flexibility, and ease of use. Understanding its behavior at different temperatures, particularly its softening point, is important for successful prints and ensuring suitability for intended uses.
What “Softening” Means for Polymers
Polymers, including PETG, do not have a sharp melting point like metals. Instead, they exhibit a glass transition temperature (Tg). This temperature marks the point where the material changes from a rigid, glass-like state to a more flexible, rubbery state. Below its Tg, a polymer is hard and brittle, but as the temperature increases beyond this point, its molecular chains gain mobility, causing the material to soften and become pliable.
The softening process for PETG involves a gradual transition where the material begins to lose its mechanical strength and rigidity. This contrasts with a melting point, which is the temperature at which a material fully transforms from a solid to a liquid. For PETG, the melting point is considerably higher than its glass transition temperature, ranging from 230°C to 260°C, which is relevant for the extrusion process during printing.
PETG’s Key Temperature Values
The glass transition temperature (Tg) for PETG falls within the range of 75°C to 85°C (167°F to 185°F). At this temperature range, PETG begins to soften and becomes more pliable, though it does not become fully liquid.
The Heat Deflection Temperature (HDT) is another important metric, indicating the temperature at which a material deforms under a specific load. For PETG, the HDT ranges from 65°C to 75°C (149°F to 167°F), depending on the specific formulation and testing conditions. This value helps determine the temperature limit for parts that need to maintain their shape under stress.
How Softening Temperature Impacts 3D Printing
PETG’s softening temperature directly influences various 3D printing parameters. A heated print bed, set between 70°C and 90°C (158°F and 194°F), helps prevent warping by keeping the print base warm enough to maintain adhesion. This temperature range is around or slightly above PETG’s Tg, which allows the first layers to adhere well and reduces internal stresses as the material cools.
The use of an enclosure can also benefit larger PETG prints. Enclosures help maintain a stable ambient temperature around the print, which minimizes rapid temperature fluctuations. This consistent thermal environment helps reduce thermal stress on the printed part, contributing to better layer adhesion and reduced warping.
Cooling fan settings are also influenced by PETG’s thermal properties. PETG requires less cooling compared to other filaments; excessive cooling can lead to delamination and weakened prints. A fan speed of 30-60% is sufficient, with some users turning off the fan for initial layers to enhance inter-layer bonding. However, too little cooling can result in stringing or sagging on overhangs.
Beyond Printing: Heat and PETG Applications
PETG’s softening temperature also dictates its suitability for various applications. Parts made from PETG are stable below 60°C, but they may begin to deform when exposed to temperatures exceeding 70°C. This means PETG components may not perform well in high-heat environments, such as inside a car on a hot day.
Post-processing techniques like annealing involve heating a printed part to a temperature near or above its glass transition temperature, between 95°C and 115°C (203°F and 239°F). This process can enhance mechanical properties like strength and heat resistance, but carries a risk of deformation or warping if not cooled slowly. Careful control of temperature and time is necessary.
For applications requiring contact with food, PETG as a raw material is considered food-safe. However, 3D printed PETG parts are not recommended for direct or prolonged food contact due to the porous nature of layer lines, which can harbor bacteria and be difficult to clean. Additionally, PETG’s softening temperature means printed items can distort in dishwashers. Handwashing is recommended if a food-safe coating has been applied.