When moulding at high temperatures, subjecting silicone to long-term heat or selecting materials, the heat resistance of silicone has a direct impact on the stability and longevity of the product. Many problems are not due to process errors, but to the misapplication of the concept of “melting point” to silicone and the underestimation of how it really behaves at high temperatures. This guide will help you see how silicone really behaves at high temperatures, and the true range of temperatures it can withstand. So you can be more informed when designing, processing, and using it.
Silicone and Silicone Melting Point
Silicone is a polymer material with a silicone-oxygen backbone. It is also a cross-linked elastomer. Its molecular chains are chemically or physically bonded to each other to form a three-dimensional lattice structure. This structural stability makes silicone both elastic and flexible. It can be used for long periods of time at temperatures ranging from about -60°C to 250°C without melting or deforming.
Why pay special attention to the melting point? When silicone is used at temperatures higher than its thermal limit, its properties change, which can have a direct impact on both design and production. If you have a clear understanding of the heat limit of silicone, you will be able to make a more appropriate judgment at the material selection stage. At the same time, in the mould design and processing parameters are set more closely to the material characteristics, to avoid the high temperature leading to performance decline or even failure, therefore improving the reliability and safety of the product.
What Happens to Silicone at High Temperatures
Does Silicone Melt, Degrade, or Burn?
The first thing to emphasize is that silicone does not have a fixed melting point and does not really melt into a liquid. As mentioned earlier, silicone is a cross-linked elastomer, forming a three-dimensional lattice structure, rather than a linear polymer or amorphous solid. Therefore, when heated to temperatures that silicone cannot withstand, it does not flow like plastic.
As the temperature rises, the properties of the silicone will gradually decline. It will slowly lose its elasticity, flexibility, and hardness. When the temperature rises further to a certain level, the chemical bonds of the silica gel will break or oxidize, which is the process of degradation. Degradation is usually characterized by a loss of elasticity, hardening of the material, and a slight yellowing of the color.
Silicone will only burn if the ambient temperature exceeds approximately 400°C. The flame is not easily sustained. During combustion, the flame is not easily sustained, and in most cases, only the surface is carbonized, and a solid residue is produced.
Factors Affecting the Heat Resistance of Silicone
Pressure Of Materials
During the processing of silicone, the pressure applied affects its thermal softening and deformation behaviour. Moderately high pressures allow for tighter molecular chains and stronger three-dimensional lattice structures, thus improving local heat resistance. However, if the pressure is too high, the material is prone to stress concentrations within the material, and this hidden stress may affect the overall thermal stability when used at high temperatures over a long period of time.
Chemical Composition
The molecular backbone of silica gel consists of Si-O bonds, and the high bonding energy of this backbone is the core of silica gel’s heat resistance. The main chain does not break easily when heated, enabling silica gel to keep its skeleton intact at high temperatures and not decompose or melt easily.
Crosslinking Density
Silicones are typically cross-linked elastomers with an internal three-dimensional lattice structure. With increased cross-linking, the molecular chains are held more firmly in place, which helps to improve heat resistance. But more cross-linking is not better. When the degree is too high, the material becomes hard and brittle. The mechanical properties decrease instead. Therefore, it should stay within an appropriate range for practical use.
Level Of Polymer and Molecular Weight
As a polymer material, the molecular weight of silica gel also affects its heat resistance. At higher molecular weights, the molecular chain is longer and more stable. Thermal degradation is less likely to occur under high temperature conditions. However, an increase in molecular weight is accompanied by a decrease in the processing fluidity of the material. The appropriate molecular weight range needs to be selected based on the application
Level Of Purity and Impurity Content
The purity of silicone has a significant impact on heat resistance. If there are unreacted low molecular components or impurities remaining in the material, these components tend to decompose first under high heat, which can cause performance to drop sooner. In contrast, high-purity silicone is more stable under high heat and maintains its performance better over long periods of time. As a result, high-purity or refined silica gel is often selected for engineering applications to ensure reliability and high temperature resistance.
Filler Type and Content (fillers)
Common fillers such as silica, glass fibres, or ceramic powders increase the mechanical strength of the material while improving thermal and dimensional stability. The type of filler and the amount of filler added will have an impact on the hardness, shrinkage, and high-temperature resistance of the silica gel, so it needs to be adjusted appropriately according to the specific needs of the application.
Curing and Processing
Silicone must be fully cured to form a stable three-dimensional lattice structure. If the curing is insufficient and the molecular chain connection is incomplete, the material is prone to elasticity decline, stickiness, or even premature aging or brittleness. While the curing conditions are appropriate, the cross-linking structure is complete, and the heat-resistant properties of the silica gel can be stably maintained.
Processing conditions are also critical. Reasonable temperature and pressure help to form a uniform, dense structure, improve thermal stability, and dimensional stability. If the moulding temperature is too high, the silica gel may be in the processing stage of local aging. Uneven or excessive pressure will introduce stresses within the material, accelerating the decay of performance when used at high temperatures.
Operating Conditions
Even if the material itself and the processing conditions are well controlled, if silicone is used for a long time in an environment close to the upper limit of temperature resistance, the thermal aging of the molecular chains will still be significantly accelerated. Over time, the material will harden, become less elastic, and its service life will be significantly shortened.
If the silicone gel works within its normal performance range most of the time, and is only exposed to higher temperatures in a few cases and for a short time, the material usually still maintains a relatively stable heat resistance and does not show any noticeable degradation in performance.
How Silicone “Melting Temperature” Is Tested and Measured
Silicones do not really have a melting point. In actual testing, we are not concerned about the temperature at which it becomes liquid, but the temperature range at which it begins to soften, degrade, or its properties begin to change. These temperature ranges are used to figure out the material selection and process design. They are also used to determine whether the product can be used under high-temperature conditions, for long-term stability are very critical.
These temperatures are usually tested in two ways: one is laboratory analysis and testing, and the other is based on visual observation of appearance and condition changes.
Laboratory Methods
Differential Scanning Calorimetry (DSC)
Equipment: DSC instrument, sample crucible, balance, tweezers, gloves and other aids
DSC is used to understand silica gel behaviour by measuring the change in heat flow through the material. A small amount of sample is placed in the instrument, the rate of temperature increase is set, the instrument heats both the sample and the reference material, and a heat flow curve is drawn. The changes in the curve tell you when the silica gel begins to soften, cross-link, or degrade. This allows you to determine its heat resistance.
Thermogravimetric Analysis (TGA)
Equipment: TGA, Atmosphere Control System
TGA is a little more intuitive. It is a measurement of the change in weight of a sample as it is heated. All that is needed is a few milligrams of silica gel, placed in an instrument and slowly heated in an atmosphere of air or nitrogen. The temperature at which the material begins to lose mass is where its degradation begins. A sample that is too thick or heated too quickly can affect the results, so it is important to keep it under control. Many times, TGA is used in conjunction with DSC or thermal microscopy so that the behaviour at high temperatures is clearer.
Direct observation
Thermal Microscopy
Equipment: Optical or Thermal Microscope with Heated Stage
You can cut a thin slice of silica gel, heat it under a microscope with a heated stage and watch it change directly. It will slowly soften and expand, and may darken or even partially decompose. By observing these phenomena, you can judge their thermal stability at different temperatures. Ensure that the thickness of the sample is consistent and that the heating rate is not too fast. This method is often combined with DSC or TGA for reference.
Capillary Melting Temperature Method
Equipment: Traditional capillary melting point apparatus (Melting Point Apparatus), including capillary tube, controlled heating source and observation device.
The method is simple. Place silica gel in the capillary tube and heat it to see if it softens or melts. This method does not determine the true melting point, but only serves as a reference. Ensure the sample is uniform, do not overfill the capillary tube and heat slowly. This method is often used in conjunction with other analyses, such as comparing different formulations or evaluating performance in engineering applications.
Heat Resistance of Different Types of Silicone
Food-grade silicone
Food-grade silicone is highly pure and does not release harmful substances. It can be used in direct contact with food. It can withstand temperatures of around 200°C over long periods, and 230–250°C over short periods. It retains its elasticity and flexibility even at high temperatures, making it ideal for baking moulds, pacifiers and various seals.
Medical-Grade Silicone
Medical-grade silicone is suitable for long-term use at temperatures of 180–200 °C and can also withstand high-temperature sterilization for short periods. It is commonly used for catheters, blood bags, and implantable devices. However, frequent sterilization can cause the material to harden and become slightly less elastic, so the frequency of use needs to be taken into account.
High-Temperature Vulcanized Silicone (HTV)
This type of silicone (HTV) has a very stable three-dimensional lattice structure, good mechanical properties and high abrasion resistance. It can withstand temperatures of up to 250°C long term and 300°C short term. It is primarily used for seals in automotive engine parts, high-temperature industrial equipment, and drying equipment. Although the high degree of cross-linking improves heat resistance, it also places greater demands on mould design and processing conditions.
Liquid Silicone Rubber (LSR / LER)
Liquid silicone rubber (LSR/LER) flows well and is easy to inject into moulds. It has long-term temperature resistance of 200–220 °C and short-term resistance of 250 °C. It is suitable for complex parts such as electronic components. It is also suitable for seals in food-grade， electronic components, medical devices and baby products. By adjusting formulations and fillers, it is possible to maintain processability and thermal stability to meet the needs of different applications.
FAQ
How Much Heat Can Silicone Withstand?
It can generally be used over a long period of time at temperatures ranging from -60°C to 200°C. Food- and medical-grade silicone can withstand temperatures between 180 and 200°C, high-temperature vulcanized silicone (HTV) can withstand temperatures up to 250°C, and liquid silicone (LSR/LER) can withstand temperatures between 200 and 220°C over a long period of time. These materials can withstand even higher temperatures for short periods of time: for example, food-grade silicone can withstand 230–250 °C, HTV can reach 300 °C, and LSR can withstand about 250 °C.
What Melts Silicone?
There is nothing that will actually melt silicone, actually. It is a cross-linked elastomer and does not liquefy when heated like ordinary plastics. When the temperature passes the tolerance limit, silicone will gradually lose its elasticity, become hard, and eventually degrade.
Will Silicone Burn In the Oven?
Not usually. Common operating temperatures for domestic ovens are in the 180-230°C range. Even when turned up to the highest setting, the temperature is only around 260-280°C. In this temperature range, silicone products of good quality will not burn. In this temperature range, as long as the quality of the qualified silicone products is good, they will not burn. Temperature to 400 ℃ or more silicone rubber may burn. It should be noted that if improperly used at high temperatures for a long time, the mechanical properties will decline. For example, the elasticity decreases, and the material hardens.
Can Boiling Water Melt Silicone?
No. The temperature of boiling water is about 100°C, which is well below the upper limit of silicone’s heat resistance. Normally, silicone will not melt in boiling water, nor will it affect its performance, nor will it release harmful substances. However, if it is boiled at high temperatures for a long period of time, the aging of the material will be accelerated. Especially the lower-quality silicone products.
Is Burning Silicone Toxic？
The smoke produced by silicone when burned is low in toxicity overall. There is no noticeable strong, irritating or corrosive odour. When the temperature rises to about 400 ℃ or more, the molecular chain of silica gel begins to break, and thermal decomposition begins to occur. This process produces mainly silica, accompanied by small amounts of carbon monoxide and carbon dioxide, as well as traces of low molecular siloxane fragments. It should be noted that although the toxicity is relatively low, it is still not suitable to inhale these fumes in case of combustion or severe overheating.
Is the Withstand Temperature the Same as the Melting Point?
Not the same thing. Temperature resistance refers to the fact that the silicone will still work at a certain temperature. And melting point is the temperature at which a material goes from solid to liquid. Silicone has no real melting point and will not melt. It only slowly degrades, hardens, and loses elasticity when it gets too hot. So in practice, it’s much more practical to look at temperature resistance than to focus on melting point.
Does Silicone Lose Its Mechanical Properties at High Temperatures?
The mechanical properties of silicone don’t break down all at once. As soon as the temperature rises, or if it is used for a long time, its elasticity slowly deteriorates, and the whole thing starts to harden. Its tear resistance also decreases, and small cracks may appear on the surface. These changes occur gradually and are related to the temperature and the length of use. So if you are in a high temperature or long-term use of the scene, it is best to choose a better heat-resistant silicone.
Final Thoughts
Overall, silicone has no real “melting point”. At high temperatures, it gradually deteriorates as the temperature rises. What you need to be concerned about is whether the temperature rating of the silicone meets the needs of the application, and whether the formulation, processing and conditions of use are compatible. These factors directly determine the long-term performance of the silicone.
Legensilico focuses on the development and use of high-performance silicone materials. We use high-purity raw materials, combined with stable cross-linking systems and mature formulation design. This makes our products maintain good elasticity and structural stability under high-temperature environments, thus prolonging their service life. Our products cover food-grade, medical-grade, LSR and high-temperature industrial silicone. They can meet the requirements of different applications in terms of safety, reliability and heat resistance. We help our customers to improve the quality and stability of their products.
