Melting point of plastic is critical information. It’s needed in many separate industrial steps. You probably know that injection molding, extrusion, and forming are standard techniques for making plastic products. These methods require specific technology to melt and work with plastic. Therefore, knowing the melting point of plastic material is critical.

If you don’t know the right temperature to heat the plastic, you’ll burn it or not melt it enough, ruining your products. Note that a good craftsman always knows his materials. You wouldn’t bake a cake without knowing the oven temperature, so why is it worth it with plastics without knowing their melting point?

In the injection molding, the plastic must flow smoothly to fill every mold corner. On the other hand, extrusion must melt to the right consistency for shaping. Even in basic formation processes, the melting point determines the manufacturing strategy.

Knowing the melting point of plastics is essential. Simple. When you master the melting point of plastics, you can control the production process. In this article, you will learn some basics about the melting point of plastic material.

What is the difference between melting point and melting range? The article also talks about different types of plastics with varying melting points. You will also be familiar with the state of plastics when heating them.

What is the Melting Point of Plastic Material?

The melting point of plastic material is the temperature at which it melts. Another way to say this is that the melting point is the temperature at which the plastic changes from solid to liquid. It seems easy, doesn’t it? But it’s not always clear-cut when it comes to plastics. Different kinds of plastic don’t melt at the same temperature; instead, they soften as the temperature changes.

Plastic material usually melts slowly in different states. In various states, there are various types of temperatures during the heating of plastics. You will know more about it in the next few sections. Before that, you must clear two concepts. What is thermoplastic, and what is thermoset? What is melting point, and what is melting range?

Thermoplastics typically have a melting range. When you heat them, they slowly turn soft and molten from solid, hard plastic. But thermosets? That’s a different story. They don’t usually melt; they break down and degrade when you heat them. You will learn more about them in the following sections.

Why does this matter for your projects? Why does the article suddenly mention this? If you’re injection molding or extruding, you must know exactly when and how your plastic melts. As you know, the raw materials are injected or pushed into the dies by injection molding and extruding. During pushing, the molten raw material must ensure an appropriate temperature. That’s why every operator must carefully maintain the correct temperature for the operation. Otherwise, your plastic parts may come with unexpected defects.

Melting Point of Plastics vs Melting Range of Plastics

We use “melting point” and “melting range ” when discussing plastic melting points.” As previously stated, a melting point occurs when a material melts into a liquid. On the other hand, a melting range is the series of locations at which a substance softens and eventually becomes liquid. Let’s investigate further.

The melting point of crystalline materials is precise and well-defined. It is firm for one moment and flowing like water for the next. However, not all polymers react like this. Some plastics do not melt immediately but rather soften progressively, due primarily to their amorphous character. Amorphous plastics don’t have a clear-cut melting. Instead, they have a melting range.

If you work with plastics in injection molding or extrusion, melting point and range play crucial roles. You need to know when your material will start to flow and when it will fully melt.

Injection molding uses an injection chamber and mold to create different plastic parts. This method is famous for creating complex plastic parts. Typical examples are toys, electric housings, automotive parts, and many consumer products. The injection chamber generally melts or softens the plastic pushed through the injection pin to the mold. During this time, maintaining the temperature is crucial.

In extrusion, on the other hand, a die and an extruder are used to make shapes of plastics. This way of making plastic is excellent for making seal strips, tubes, and sheets. The raw material is removed from the bin and sent to the extruder barrel. This machine has big screws that move it forward. Both of these things happen at the same time in the extruder barrel. The melting point and melting ranges are critical in this case.

Stages of Melting During Heating Plastics

In general, plastics have both melting points and melting ranges. When heated, they undergo two stages before melting: initial and full. These two stages significantly affect the quality of the final plastic product. When working with plastics, you must use a controlled environment.

Stage #1 Initial Melting

Plastics show subtle signs the first time, just like butter in the initial stage. At this point, the plastic’s solid structure begins to loosen and soften. It’s not completely liquid yet, but the material loses its rigidity. This stage is critical. If you heat too fast, it might cause uneven melting or even damage the material.

Plastics are frequently rather stable during the initial melting period. However, they are generally pliable. It’s similar to the difference between solids and liquids: pliable enough to mold but rigid enough to retain form.

This stage is ideal for the plastic-forming method. You must be careful here, especially when maintaining the temperature rate. You might find a few defects if the heat is ramped up too quickly. Typical defects you might see are warping uneven melting, or surface degradation.

Stage #2 Full Melting

If you continue to heat the pliable plastic, it will melt completely. This is the point at which the plastic turns into a liquid. The substance loses all stiffness and flows freely. You can then use it to mold or extrude. The concentration of plastic liquid is very thick, making it easy to handle.

This is the stage when you will primarily work with plastic. It is ideal for plastic injection and extrusion methods. However, you must be careful with timing though. If you heat it too long, you risk burning or degrading the plastic. And once that happens, there’s no going back.

Another question people often ask is what the right temperature is for full melting. Different plastics have different melting points. You have to know your material. For example, polyethylene melts at a different temperature than nylon. You will know the exact value at the end of this article.

Melting Characteristics of Plastics

Plastic has varying melting behaviors. The way plastic melts can make or break your manufacturing process. Some plastics melt evenly, while others often over various temperatures.

The characteristics of plastic mainly depend on two main criteria. (1) Is it thermoplastic or thermosetting? (2) Is it crystalline or amorphous? You can choose the right plastic for your project when you have enough information on these two factors.

Thermoplastics vs Thermosets

Thermoplastics provide flexibility in the production process. They may be melted down, reformed, and reused. These materials are great for ever-changing designs. Thermosets, on the other hand, are exactly the opposite. It does not melt but instead degrades and breaks over time. They are perfect for long-term use because they do not melt and cannot be reshaped. Besides, thermosetting plastics are high-strength structures.

So, which one might be right for your project? The table below lists the characteristics of each plastic.

Crystalline vs Amorphous Materials

When you consider thermoplastics, you have two options: crystalline and amorphous. These two thermoplastics also behave differently when heated. Crystalline plastics have a clear-cut melting point. Because of this, they are easy to handle during injection molding or extrusion. On the other hand, amorphous plastics soften over a range of temperatures. This can be both beneficial and irritating. The irritating part is that your plastic might deform while cooling if you cannot control the temperature properly.

So, which one might be right for your project? The table below lists the characteristics of each plastic.

The Three States of Plastics During Heating

Heating plastic does not transform it into a liquid only. It passes several phases, each showing the different conditions of the plastic. Under this situation, one usually discusses three states. Let us transcend these states.

State #1 Glassy State

The glassy state is typically the material’s rigid, brittle, and tough state. When heated, plastic reaches the transition temperature at a certain time. When it reaches this level, it shows a glassy state, thus the name. In this phase, the plastic molecules are tightly together. If you apply stress to it, it won’t change any of its structures.

State #2 High Elastic State

As the temperature rises, plastic enters the high elastic or rubber state. At this moment, plastic becomes stretchy and flexible but not flowing. The plastic gets more flexible and stretches but is not nearly meltable. Though the molecules now move more freely and relax, they still cling to one another.

State #3 Viscous Flow State

Finally, the plastic finds its viscous flow condition. This is the intriguing part. At this point, the plastic moves more like a thick liquid. Plastic can be shaped and molded as the unrestricted movement of its molecules enables it. This is the moment you might pour plastic into the mold.

Three Key Temperatures of Plastics During Heating

You are now familiar with three significant states of plastic. In this section, you will learn how temperatures affect these states. Note that each temperature point is critical in how the plastic behaves and how you will process it.

#1 Glass Transition Temperature (Tg)

This is the temperature responsible for the glass state of plastics, hence the name glass transition temperature (Tg). At this time, the plastic is stiff, brittle, and tough. The next step is the elastic state, in which the plastic turns rubbery. It hasn’t melted yet, but it is more pliable. This temperature is necessary for both polycarbonate (PC) and polystyrene.

#2 Melting Temperature (Tm) or Flow Temperature

The melting temperature is also known as the flow temperature. It is where the plastic melts. For crystalline plastic, this is a specific temperature. If you heat the plastic to this temperature, it moves from solid to liquid. Then, it is to be molded or extruded.

However, amorphous plastics do not melt in the conventional sense. They first soften before gradually becoming liquid.

In injection molding and extrusion, obtaining the flow temperature is critical for properly shaping the material. If the plastic is too cold, it will not flow effectively, resulting in poor performance.

#3 Decomposition Temperature

The final temperature is the breakdown temperature. It is typically utilized as a danger zone. When you heat a plastic above its melting or flow temperature, it breaks down chemically. Not only will the material lose its properties, but it could also release harmful gases.

If you push the plastic too far, it will go past its breaking point. Decomposition temperatures differ depending on the type of plastic, but they are always a point to avoid.

Why is Melting Point Necessary for Injection Molding, Extrusion, and Formation?

In plastic manufacture, melting or softening plastic is a regular operation—usually, injection molding, extrusion, and forming start on this basis. Therefore, the melting point of polymers becomes important here.

Role #1 Ensures Optimal Flow

Plastics’ melting points play the first and most crucial role in ensuring optimal flow. You are already familiar with flow temperature or melting temperature. The melting point ensures the plastic becomes fluid enough to flow smoothly. If it’s too cold, it won’t fill molds or flow through extruders properly. However, if it is too hot, the plastic might degrade.

Role #2 Prevents Decomposition

As we already said, plastic breaks down when heated above its melting point. This temperature, which can destroy your material, is often called the breakdown temperature. The melting point of plastics tells you what temperature your process can’t go above.

Role #3 Determines Cycle Time Efficiency

The melting point determines how quickly or slowly a process can proceed. The plastic will take longer to melt or cool down if you don’t reach the proper temperature. Mastering the melting point helps shorten cycle times and cut production delays.

Role #4 Affects Material Strength

What happens when plastic is over- or under-heated? Its structural integrity has been damaged. The melting point determines how plastic hardens or sets. Poorly regulated melting points might result in weak or brittle products.

Role #5 Enables Uniformity and Precision

Properly maintaining plastics’ melting points can ensure consistent parts every time. Whether it’s injection molding or extrusion, the plastic has to flow evenly to prevent defects like warping or uneven surfaces. Correct melting also helps ensure that parts maintain precise dimensions and tolerances.

Melting Point of Common Plastics

In the plastic industry, a wide range of plastics are used. If we make a list of them, this article might become huge. In the following, we have highlighted a few common types of plastics and their melting points.

Frequently Asked Questions

Which plastic has the highest melting point?

Among the most common plastics, PTFE has the highest melting point. It is also known as Polytetrafluorethylene. The general melting point of this plastic is 327C or 620F. One of the best things about this material is its stability. PTFE is highly stable in a wide range of temperatures, from -200C to 260C. As a result, people use it in many applications.

Will plastic melt at 170 degrees?

As you know, there is a wide range of plastics available. Plastic melting is, therefore, not the same for everyone. The kinds of plastics determine it mainly. Low melting point polymers such as LDPE and HDPE exist. They usually melt at 170 degrees.

Which plastic has the lowest melting point?

Polyethylene, sometimes called PE plastic, is one of the most often used forms of plastic. Its melting point is between 100C and 180C, usually among the lowest. This plastic is extensively used in plastic bags and containers.

What is the hardest plastic to melt?

Among the tough-to-melt plastics, PTFE is one of the hardest plastics. It comes with a melting point of around 327°C (620°F). This plastic is used in a wide range of applications.

Do all plastics have different melting points?

Yes, they do. Different types of plastics are used in many applications. Why is there such diversity? They have unique physical and chemical properties. Some melt at low heat, while others melt at high heat.

Summary

We mostly covered plastic behavior under heat throughout this paper. As you have observed, every form of plastic has somewhat varied melting points. Furthermore, the melting temperature changes depending on the type of plastic.

The melting point of plastics is crucial for various manufacturing processes. Typical factory processes are injection molding, extrusion, and plastic forming. In each method, the melting point of plastics plays a critical role. Failure to maintain the right melting temperature may lead to many defects.

If you have any questions, contact our customer support team. We have a team of experts who are always happy to assist you. if you are looking for suitable plastic material for your project, you can go to page on how to select the best injection molding material to find the best option for your project, or you can contact us for support.