CB6950 Polybutylene Terephthalate Rod (PBT Rod)

Polybutylene Terephthalate Rod (PBT Rod) Description

Polybutylene Terephthalate (PBT) rods are semi‐crystalline engineering thermoplastics that contain a repeating molecular unit of aromatic terephthalate groups linked by aliphatic butylene segments. This structure produces 30–45% crystallinity in processed rods, with spherulitic domains (5–20 μm diameter) that determine anisotropic behaviour. The rods exhibit high rigidity (flexural modulus: 2 400–2 600 MPa) but low ductility, with a tensile strength of 80 MPa and an elongation at break of 4–6%. A notched Izod impact strength of 70 J/m indicates brittle fracture due to crystalline lamellae thickness (10–15 nm) restricting plastic deformation. The Shore D hardness of 90 permits precision machining; however, it increases vulnerability to stress concentrators.

Thermally, PBT rods have a glass transition temperature (Tg) of 40–60°C and a melting point (Tm) of 224°C. The low thermal conductivity (0.24 W/m·K) facilitates thermal insulation, while the heat deflection temperature (HDT) of 110°C at a 1.82 MPa load indicates moderate thermal stability. Continuous service is limited to 100°C because hydrolysis is accelerated above this threshold; short‐term exposure to 150°C is acceptable provided the moisture content remains below 0.05%. Significant linear expansion anisotropy (∥ flow: 6×10⁻⁵ K⁻¹ vs. ⊥ flow: 10×10⁻⁵ K⁻¹) requires design compensation to maintain dimensional stability.

Electrically, the non‐polar molecular backbone of PBT delivers stable insulation. Volume resistivity (10¹⁵ Ω·cm), surface resistivity (10¹⁴ Ω) and dielectric strength (22 kV/mm) remain consistent up to 120°C. The dielectric constant (ε=3.3 at 1 MHz) shows minimal frequency dispersion (Δε<0.1 from 50 Hz–1 MHz), while the dielectric loss (tan δ=0.015) confirms low hysteresis heating.

Chemically, PBT rods resist weak acids, bases and hydrocarbons but are subject to hydrolysis via ester group scission in humid environments above 60°C. Equilibrium water absorption is 0.1% at 23°C/60% RH (Fickian diffusion kinetics, D=3×10⁻⁹ cm²/s). Ultraviolet exposure causes chain scission (yellowing index ΔYI>15 after 500 h Xenon arc exposure); this effect may be reduced by incorporation of carbon black or UV stabilisers. Degradation initiates at 280°C (TGA onset in N₂), with the release of tetrahydrofuran and acrolein.

Polybutylene Terephthalate Rod (PBT Rod) Applications

PBT rods are employed as machinable stock for components that require electrical insulation, dimensional stability and chemical resistance. In electrical engineering, they are used to manufacture terminal blocks, circuit breaker housings and relay insulators. The volume resistivity (≥10¹⁵ Ω·cm) and dielectric strength (22 kV/mm) ensure prevention of tracking or arcing in high‐voltage environments at temperatures up to 100°C continuous. The automotive sector utilises machined rods for fuel system components (for example, fuel pump housings and sensor mounts), where hydrolysis resistance and dimensional stability (water absorption <0.1% at 23°C/60% RH) preserve sealing integrity against biofuel blends (ethanol, biodiesel).

Industrial applications include wear‐resistant gears, conveyor bearings and valve seats. The low friction coefficient (μ=0.15–0.25 vs. steel) and rigidity (flexural modulus 2 400 MPa) allow operation under mechanical loads. In chemical processing, rods are CNC‐machined into pump impellers, flowmeter rotors and laboratory instrument handles that resist dilute acids/alkalis and hydrocarbons (e.g. isooctane, toluene). Emerging applications encompass medical device grips and HVAC damper actuators, where UL 94 V‐0 flammability compliance and low ionic contamination (Na⁺/Cl⁻ <1 ppm) satisfy regulatory requirements.

The material’s anisotropic thermal expansion (∥ flow: 60×10⁻⁶/K vs. ⊥ flow: 100×10⁻⁶/K) necessitates machining perpendicular to the extrusion axis in order to maintain dimensional accuracy. Prolonged exposure above 150°C is not permitted due to the risk of thermal degradation, and contact with strong mineral acids (e.g. >10% H₂SO₄) is prohibited because ester hydrolysis is accelerated. PBT’s balance of machinability (achievable surface finish Ra <3.2 μm), creep resistance (<1% strain at 80 MPa over 1 000 h) and cost efficiency renders it a viable alternative to metals, nylons and acetals in electromechanical systems operating below 120°C.

Polybutylene Terephthalate Rod (PBT Rod) Packaging

Our products are packaged in customised cartons of varying sizes according to the material dimensions. Small items are securely packed in PP boxes, while larger items are placed in customised wooden crates. We adhere strictly to packaging customisation and adopt appropriate cushioning materials in order to provide protection during transportation.

Packaging: Carton, Wooden Box, or Customised.

Kindly review the packaging details provided for your reference.

Manufacturing Process

1.       Testing Method

(1)    Chemical Composition Analysis – Techniques such as GDMS or XRF are used to verify compliance with established purity requirements.

(2)    Mechanical Properties Testing – This testing includes assessments of tensile strength, yield strength and elongation to quantify material performance.

(3)    Dimensional Inspection – Measurements of thickness, width and length are conducted to ensure adherence to specified tolerances.

(4)    Surface Quality Inspection – Visual and ultrasonic examinations are performed to detect any defects such as scratches, cracks or inclusions.

(5)    Hardness Testing – Material hardness is determined to confirm uniformity and mechanical reliability.

Please refer to the SAM testing procedures for detailed information.

Polybutylene Terephthalate Rod (PBT Rod) FAQs

Q1. What machining parameters prevent cracking in precision components?

Maintain cutting speeds of 200–300 m/min using carbide tools. Use feed rates of 0.1–0.3 mm/rev and apply compressed air cooling rather than water‐based coolants. Ensure that tool geometry provides a positive rake angle of at least 10° to minimise localised heating; temperatures exceeding 120°C can induce microcracks. Post‐machining stress‐relieving at 80°C for 2 hours mitigates residual stresses.

Q2. How does humidity affect dimensional stability in electrical insulators?

Relative humidity exceeding 60% causes moisture absorption to rise above 0.3% compared with an equilibrium of 0.1%, resulting in up to 0.15% linear expansion. For critical applications, pre‐drying at 80°C for 4 hours is required to achieve a moisture content below 0.05%. Swelling perpendicular to the extrusion direction is approximately 30% greater.

Q3. What chemical exposures cause catastrophic hydrolysis?

Avoid prolonged contact with strong acids (for example, 10% H₂SO₄ at 60°C causes degradation within 500 hours).

Also avoid strong bases (for example, 5% NaOH at 50°C results in a 50% loss of strength within 300 hours).

Furthermore, avoid superheated steam (above 110°C at 100% RH initiates ester bond scission within 24 hours).

Related Information

1.       Common Preparation Methods

PBT rods are produced by melting dried plastic pellets and extruding them through a shaped die. Initially, raw PBT pellets are baked at 120–130°C for at least 4 hours to remove moisture. The dried pellets are then fed into a heated barrel fitted with a rotating screw, where they melt into a viscous liquid at 240–255°C. The molten plastic is subsequently forced through a rod‐shaped die.

The extruded rod, still soft, is immediately passed into a cooling tank with water at 15–25°C, which hardens its surface. It then proceeds through a warm chamber (90–110°C) for 2–4 hours. This slow reheating permits uniform crystal formation within the plastic, thereby preventing the formation of weak areas.