Analysis and Key Material Data Comparison of Linear Thermal Expansion Coefficient (CLTE) for Specialty Engineering Plastics

CLTE Example of PEEK Material

Reference can be made to the CLTE data of Victrex KETASPIRE® PEEK pure resin injection molding grade KT-880.

Comparing KETASPIRE® PEEK unreinforced and modified reinforced grades: KT-820 CF30 with 30% carbon fiber addition has a lower CLTE.

CLTE Comparison of PPS Materials

DIC PPS:

- PPS-GF40: grades FZ-1140 (cross-linked type), FZ-2140 (linear type)

- PPS-GFMF65: grades FZ-3600 (cross-linked type), FZ-6600 (linear type)

- Toughened grades: Z-230, Z-650

Similar to mechanical properties, the CLTE of linear PPS exhibits anisotropy. As shown in Figure 4.21, the CLTE curves differ significantly in the fiber direction (FD) and transverse direction (TD), especially when there is strong orientation. If the direction is unknown, the median value between FD and TD can be taken.

The CLTE of DIC fiber-reinforced PPS can be as low as 2.4 × 10⁻⁵ m/mK, which is comparable to aluminum die castings.

Toray PPS:

CLTE definition: The ratio of the initial size of the molded product to the thermal expansion deformation when the temperature rises by 1K, calculated from the TMA (Thermomechanical Analysis, measuring displacement by changing temperature under constant load) curve, usually referring to the average value within a specific temperature range.

The TMA curve shows that after exceeding the glass transition temperature (Tg ≈ 90°C–95°C), the CLTE of PPS resin increases significantly. Therefore, the average CLTE over a wide temperature range will increase with temperature (e.g., unreinforced PPS). The solution is to divide the temperature range above and below Tg and calculate separately to reduce the deviation rate.

The CLTE of reinforced PPS in the flow direction (FD) and vertical direction is different, affected by the type, content of reinforcing materials, and flow orientation (anisotropy).

CLTE data of samples (10 x 5 x 3 mm) cut from the center of a flat plate (80×80×3 mm) with relatively low anisotropy. CLTE decreases with the increase of reinforcing material content, and cross-linked PPS usually has lower CLTE than linear PPS. The grade A575W20B with inorganic minerals added has little change in CLTE at high temperatures above Tg.

Syensqo Ryton® PPS:

Comparing grades: R-7-190BL and R-7-120BL (both 65% glass fiber/mineral reinforced). Among them, R-7-190BL has a smaller expansion rate in the TD direction.

CLTE Highlights of Other Engineering Plastics

- Solvay PPA AMODEL®: The CLTE of AS-1566HS in the FD direction is comparable to that of stainless steel, making it an excellent choice for low warpage applications.

- Polyplastics PPS DURAFIDE®: The CLTE of grade 8670A64 in the MD and TD directions is basically the same, which can be maintained at 2.0 × 10⁻⁵ m/mK below 60°C.

Data sources: The above CLTE information is derived from the official design guidelines of DIC, Polyplastics, Syensqo, and Toray.