- What happens when a material is heated?
- What is coefficient of linear thermal expansion (CLTE)?
- What is the formula of CLTE?
- What are the units of the CLTE?
- What factors affect the CLTE of plastics?
- What are the applications of the CLTE?
- What are the techniques and test methods to measure CLTE?
- What is the linear CLTE values of several plastics?
What happens when a material is heated?
Under the effects of increasing temperature, any material will expand. This can lead to:
- significant changes in the dimensions
- unequal shrinkage (warpage), or
- internal stress
What is the coefficient of linear thermal expansion (CLTE)?
The coefficient of linear thermal expansion is a material property that:
- Characterizes the ability of a plastic to expand when the temperature increases.
- Estimate the dimensional stability of a developed part when temperature varies.
It is abbreviated as CLTE.
What is the formula of CLTE?
The CLTE is referred to as "α." It is obtained by dividing the linear expansion per unit length by the change in temperature. The formula for the linear coefficient for plastic and polymer materials is:
α = ΔL/(L0 * ΔT)
where
- α is the coefficient of linear thermal expansion per degree Celsius.
- ΔL is the change in length of test specimen due to heating or to cooling.
- L0 is the original length of specimen at room temperature.
- ΔT is the temperature change in °C, during the test.
When reporting the mean coefficient of thermal expansion specify the temperature ranges.
What are the units of the coefficient of linear thermal expansion?
The units of coefficient of linear expansion are:
- Degree Celcius (°C-1)
- Kelvin (K-1)
- Degree Fahrenheit(°F-1)
What factors affect the CLTE of plastics?
Fibers and Fillers
Fibers and other fillers significantly reduce thermal expansion. The factors that pose a great impact on the linear coefficient of thermal expansion are:
- degree of anisotropy of the filler and the
- orientation of the filler
Watch Course: Efficient Optimization of Fillers in Thermoplastics
Temperature
The
temperature is directly proportional to CLTE. The magnitude of CTE increases with rising temperature.
Graph showing the CLTE vs. Temperature of plastics
Molecular Orientation
Molecular orientation also affects the thermal expansion of plastics. It is often affected by the cooling time during processing. This is especially true with
semi-crystalline polymers whose crystallization process requires time.
What are the applications of the coefficient of linear thermal expansion?
The thermal expansion difference develops internal stresses and stress concentrations in the polymer. This allows premature failure to occur. Find out the top 3 roots causes to
avoid plastic failure »
CLTE is important for the economics of production. It is also necessary for the quality and functioning of products. It determines the:
- Design to predict shrinkage in injection molded parts.
- Dimensional behavior of structures subject to temperature changes.
- Thermal stresses that can occur and cause the failure of a solid artifact composed of different materials. This failure is subjected to a temperature excursion. For example, to predict efficient material bonding or while using plastics with metals.
What are the techniques and test methods to measure CLTE?
The standards to measure the CLTE of thermoplastics and thermosets are as follows. These plastics can be either in filled or unfilled form or in sheet or molded form.
Dilatometry Technique
It is the widely used technique in which the specimen is heated in a furnace. The displacement of the ends (lengths) of the specimen are transmitted to a sensor by means of push rod. Push rods may be of several types such as:
- the vitreous silica type,
- the high-purity alumina type, or
- the isotropic graphite type.
Standards to calculate CLTE of plastics using Dilatometry:
- ASTM D696 – This method determines the CLTE for plastics having values greater than 1 µm/(m.°C). This method uses a vitreous silica dilatometer. The nature of most plastics and the construction of the dilatometer make −30 to +30°C (−22°F to +86°F) a convenient temperature range. This range covers the temperatures in which plastics are most commonly used.
- ASTM E228 – This standard covers a temperature range other than −30°C to 30°C. It determines the CLTE of solid materials with a push-rod dilatometer.
Thermomechanical Analysis (TMA)
The linear thermal coefficient is measured using a thermomechanical analyzer. This instrument consists of:
- a specimen holder
- a probe
- a transducer
The probe transmits changes in length to a transducer that translates the movements of the probe into an electrical signal.
Standards to calculate CLTE of plastics using TMA:
- ASTM E831 (and ISO 11359-2) –These methods are applicable to solid materials that exhibit sufficient rigidity. It is applicable from −120 to 900°C. This range can be extended depending on the instrumentation and calibration materials used. The lower limit for CTE with this method is 5 × 10-6/K (2.8 × 10-6/°F), but it may be used at lower or negative expansion levels with decreased accuracy and precision.
Interferometry Technique
The displacement of the specimen ends is measured with optical interference techniques. This is done in terms of the number of wavelengths of monochromatic light. The precision of this instrument is greater than with dilatometry. Interferometry is not used much above 700°C (1290°F) as it relies on the optical reflectance of the specimen surface.
The Displacement of the Specimen Ends is Measured with Optical Interference Techniques (Source: Researchgate)
Standards to calculate CLTE using Interferometry technique:
-
ASTM E289 determines the CLTE of rigid solids with interferometry from –150 to 700°C (–240 to 1290°F). It is more applicable to materials:
- Having low or negative CTE in the range of <5 × 10-6/K (2.8 × 10-6/°F). Find suitable low CLTE grades »
- Where only limited thickness lengths of other higher expansion coefficient materials are available.
What is the linear coefficient of thermal expansion values of several plastics?
In the service temperature range, the coefficient of linear thermal expansion lies between:
- Ca. 0.6 x 10-4 to 2.3 x 10-4 K-1 for most of the thermoplastics
- Ca. 0.2 x 10-4 to 0.6 x 10-4 K-1 for most of the thermosets
Click to find polymer you are looking for:
A-C |
E-M |
PA-PC |
PE-PL |
PM-PP |
PS-X
| Polymer Name |
Min Value (10-5 /°C) |
Max Value (10-5 /°C) |
| ABS - Acrylonitrile Butadiene Styrene |
7.00 |
15.00 |
| ABS Flame Retardant |
6.00 |
9.00 |
| ABS High Heat |
6.00 |
10.00 |
| ABS High Impact |
6.00 |
13.00 |
| ABS/PC Blend - Acrylonitrile Butadiene Styrene/Polycarbonate Blend |
4.00 |
5.00 |
| ABS/PC Blend 20% Glass Fiber |
1.80 |
2.00 |
| ABS/PC Flame Retardant |
3.00 |
4.00 |
| ASA - Acrylonitrile Styrene Acrylate |
6.00 |
11.00 |
| ASA/PC Blend - Acrylonitrile Styrene Acrylate/Polycarbonate Blend |
7.00 |
9.00 |
| ASA/PC Flame Retardant |
7.00 |
8.00 |
| ASA/PVC Blend - Acrylonitrile Styrene Acrylate/Polyvinyl Chloride Blend |
0.00 |
9.00 |
| CA - Cellulose Acetate |
8.00 |
18.00 |
| CAB - Cellulose Acetate Butyrate |
10.00 |
17.00 |
| Cellulose Diacetate- Pearlescent Films |
2.15 |
2.15 |
| Cellulose Diacetate-Gloss Film |
2.15 |
2.15 |
| Cellulose Diacetate-Integuard Films |
1.00 |
1.50 |
| Cellulose Diacetate-Matt Film |
2.15 |
2.15 |
| Cellulose Diacetate -Window Patch Film (Food Grade) |
2.15 |
2.15 |
| Cellulose Diacetate-Clareflect metallized film |
1.50 |
1.50 |
| Cellulose diacetate-Flame retardant Film |
0.64 |
0.64 |
| Cellulose Diacetate-High Slip Film |
2.15 |
2.15 |
| Cellulose Diacetate-High Slip Film |
2.15 |
2.15 |
| CP - Cellulose Propionate |
10.00 |
17.00 |
| COC - Cyclic Olefin Copolymer |
6.00 |
7.00 |
| CPVC - Chlorinated Polyvinyl Chloride |
6.00 |
8.00 |
| ECTFE |
6.00 |
9.00 |
| EVA - Ethylene Vinyl Acetate |
16.00 |
20.00 |
| FEP - Fluorinated Ethylene Propylene |
8.00 |
10.00 |
| HDPE - High Density Polyethylene |
6.00 |
11.00 |
| HIPS - High Impact Polystyrene |
5.00 |
20.00 |
| HIPS Flame Retardant V0 |
5.00 |
15.00 |
| Ionomer (Ethylene-Methyl Acrylate Copolymer) |
10.00 |
17.00 |
| LCP - Liquid Crystal Polymer |
0.30 |
7.00 |
| LCP Carbon Fiber-reinforced |
0.10 |
6.00 |
| LCP Glass Fiber-reinforced |
0.10 |
6.00 |
| LCP Mineral-filled |
0.90 |
8.00 |
| LDPE - Low Density Polyethylene |
10.00 |
20.00 |
| MABS (Transparent Acrylonitrile Butadiene Styrene) |
8.00 |
11.00 |
| PA 11 - (Polyamide 11) 30% Glass fiber reinforced |
3.00 |
15.00 |
| PA 11, Conductive |
9.00 |
15.00 |
| PA 11, Flexible |
9.00 |
15.00 |
| PA 11, Rigid |
9.00 |
15.00 |
| PA 12 (Polyamide 12), Conductive |
9.00 |
15.00 |
| PA 12, Fiber-reinforced |
9.00 |
15.00 |
| PA 12, Flexible |
9.00 |
15.00 |
| PA 12, Glass Filled |
9.00 |
15.00 |
| PA 12, Rigid |
9.00 |
15.00 |
| PA 46, 30% Glass Fiber |
2.00 |
2.00 |
| PA 6 - Polyamide 6 |
5.00 |
12.00 |
| PA 6-10 - Polyamide 6-10 |
6.00 |
10.00 |
| PA 66 - Polyamide 6-6 |
5.00 |
14.00 |
| PA 66, 30% Glass Fiber |
2.00 |
3.00 |
| PA 66, 30% Mineral filled |
4.00 |
5.00 |
| PA 66, Impact Modified, 15-30% Glass Fiber |
2.00 |
3.00 |
| PA 66, Impact Modified |
5.00 |
14.00 |
| PAI - Polyamide-Imide |
3.00 |
4.00 |
| PAI, 30% Glass Fiber |
1.00 |
2.00 |
| PAI, Low Friction |
2.00 |
3.00 |
| PAN - Polyacrylonitrile |
6.00 |
7.00 |
| PAR - Polyarylate |
5.00 |
8.00 |
| PARA (Polyarylamide), 30-60% glass fiber |
1.40 |
1.80 |
| PBT - Polybutylene Terephthalate |
6.00 |
10.00 |
| PBT, 30% Glass Fiber |
2.00 |
5.00 |
| PC (Polycarbonate) 20-40% Glass Fiber |
2.00 |
4.00 |
| PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant |
2.00 |
4.00 |
| PC - Polycarbonate, high heat |
7.00 |
9.00 |
| PCL - Polycaprolactone |
16.00 |
17.00 |
| PCTFE - Polymonochlorotrifluoroethylene |
4.00 |
7.00 |
| PE - Polyethylene 30% Glass Fiber |
5.00 |
5.00 |
| PEEK - Polyetheretherketone |
4.70 |
10.80 |
| PEEK 30% Carbon Fiber-reinforced |
1.50 |
1.50 |
| PEEK 30% Glass Fiber-reinforced |
1.50 |
2.20 |
| PEI - Polyetherimide |
5.00 |
6.00 |
| PEI, 30% Glass Fiber-reinforced |
2.00 |
2.00 |
| PEI, Mineral Filled |
2.00 |
5.00 |
| PEKK (Polyetherketoneketone), Low Crystallinity Grade |
77.00 |
77.00 |
| PESU - Polyethersulfone |
5.00 |
6.00 |
| PESU 10-30% glass fiber |
2.00 |
3.00 |
| PET - Polyethylene Terephthalate |
6.00 |
8.00 |
| PET, 30% Glass Fiber-reinforced |
2.00 |
5.00 |
| PET, 30/35% Glass Fiber-reinforced, Impact Modified |
1.50 |
2.00 |
| PETG - Polyethylene Terephthalate Glycol |
8.00 |
8.00 |
| PFA - Perfluoroalkoxy |
8.00 |
12.00 |
| PI - Polyimide |
5.50 |
5.50 |
| PLA - Polylactide |
8.50 |
8.50 |
| PMMA - Polymethylmethacrylate/Acrylic |
5.00 |
9.00 |
| PMMA (Acrylic) High Heat |
4.00 |
9.00 |
| PMMA (Acrylic) Impact Modified |
5.00 |
9.00 |
| POM - Polyoxymethylene (Acetal) |
10.00 |
15.00 |
| POM (Acetal) Impact Modified |
12.00 |
13.00 |
| POM (Acetal) Low Friction |
10.00 |
12.00 |
| POM (Acetal) Mineral Filled |
8.00 |
9.00 |
| PP - Polypropylene 10-20% Glass Fiber |
4.00 |
7.00 |
| PP, 10-40% Mineral Filled |
3.00 |
6.00 |
| PP, 10-40% Talc Filled |
4.00 |
8.00 |
| PP, 30-40% Glass Fiber-reinforced |
2.00 |
3.00 |
| PP (Polypropylene) Copolymer |
7.00 |
17.00 |
| PP (Polypropylene) Homopolymer |
6.00 |
17.00 |
| PP, Impact Modified |
7.00 |
17.00 |
| PPA - Polyphthalamide |
5.40 |
5.40 |
| PPA, 30% Mineral-filled |
7.10 |
7.20 |
| PPA, 33% Glass Fiber-reinforced |
1.00 |
1.20 |
| PPA, 33% Glass Fiber-reinforced – High Flow |
0.90 |
1.10 |
| PPA, 45% Glass Fiber-reinforced |
0.73 |
0.75 |
| PPE - Polyphenylene Ether |
3.00 |
7.00 |
| PPE, 30% Glass Fiber-reinforced |
1.50 |
2.50 |
| PPE, Flame Retardant |
3.00 |
7.00 |
| PPE, Impact Modified |
4.00 |
8.00 |
| PPE, Mineral Filled
|
2.00 |
5.00 |
| PPS - Polyphenylene Sulfide |
3.00 |
5.00 |
| PPS, 20-30% Glass Fiber-reinforced |
1.00 |
4.00 |
| PPS, 40% Glass Fiber-reinforced
|
1.00 |
3.00 |
| PPS, Conductive
|
1.00 |
9.00 |
| PPS, Glass fiber & Mineral-filled |
1.00 |
2.00 |
| PS (Polystyrene) 30% glass fiber
|
3.50 |
3.50 |
| PS (Polystyrene) Crystal |
5.00 |
8.00 |
| PS, High Heat |
6.00 |
8.00 |
| PSU - Polysulfone
|
5.00 |
6.00 |
| PSU, 30% Glass fiber-reinforced
|
2.00 |
3.00 |
| PSU Mineral Filled
|
3.00 |
4.00 |
| PTFE - Polytetrafluoroethylene
|
7.00 |
20.00 |
| PTFE, 25% Glass Fiber-reinforced
|
7.00 |
10.00 |
| PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced
|
2.00 |
4.00 |
| PVC, Plasticized |
5.00 |
20.00 |
| PVC, Plasticized Filled
|
7.00 |
25.00 |
| PVC Rigid
|
5.00 |
18.00 |
| PVDC - Polyvinylidene Chloride
|
10.00 |
20.00 |
| PVDF - Polyvinylidene Fluoride
|
8.00 |
15.00 |
| SAN - Styrene Acrylonitrile |
6.00 |
8.00 |
| SAN, 20% Glass Fiber-reinforced
|
2.00 |
4.00 |
| SMA - Styrene Maleic Anhydride
|
7.00 |
8.00 |
| SMA, 20% Glass Fiber-reinforced
|
2.00 |
4.00 |
| SMA, Flame Retardant V0
|
2.00 |
6.00 |
| SRP - Self-reinforced Polyphenylene |
3.00 |
3.00 |
| UHMWPE - Ultra High Molecular Weight Polyethylene |
13.00 |
20.00 |
| XLPE - Crosslinked Polyethylene
|
10.00 |
10.00 |