What is polymer matrix composite?

The polymer matrix composite is described as a composite material that contains some polymer in the form of either fibers or powder. Polymer matrix composites are also known in short as PMC's.

The polymer matrix composite is a lightweight and corrosion resistive element of very high strength and is commonly used in manufacturing automobile parts, airplane parts, and many others. It is also having a low cost and simple manufacturing process.

Classification of polymer matrix composites

Following are the various types of polymer matrix composites:

• Thermoset
• Thermoplastic
• Rubber

Thermoset

Thermoset is a polymer made up of a combination of heavily branched molecules. It has the property of undergoing chemical reactions by the action of heat, light, catalyst, and others. It is made by mixing two components, resin, and hardener. The molecular structure of thermoset or thermosetting plastic is shown as:

Thermoplastic

Thermoplastic is described as a polymer material made by individual molecules in a linear structure without any chemical linkage between them. The molecular weight of thermoplastic is high, and it is moldable at room temperature. Thermoplastic can be easily recycled. The molecular structure of thermoplastic mole is shown as:

Processing of polymer matrix composition

Following are the various manufacturing processes used for processing thermoset or thermosetting matrix composites:

• Hand layup technique
• Spray up technique
• Filament winding
• Pultrusion
• Resin transfer molding
• Autoclave molding

Hand layup technique

The hand layup technique is an open mold shaping technique in which consecutive layers of resin and reinforcement are manually applied to an open mold to build the laminated composite structure. It is a manual, time taking, and labor-consuming method.

The diagrammatical representation of the filament winding method is shown as: of the hand layup technique or method is shown as:

Following are the advantages of the hand layup technique:

• Low tooling cost
• Widely used
• Produce large and complex products

Following are disadvantages of the hand layup technique:

• Low volume process
• Emits styrene
• Quality of the product depends on the skill of labor.

Spray up technique

A liquid resin mixture containing reinforcing fibers is sprayed by two different sprays on the mold surface in the spray-up technique. It permits the rapid formation of the uniform composite coating. It is used for producing light-loaded structural panels like truck fairings, small boats, and many others.

The diagrammatical representation of the spray-up technique is shown as:

Following are the advantages of spray up technique:

• Design flexibility
• Produce complex-shaped objects

Following are the disadvantages of spray up technique:

• Labor-based process
• The waste factor is high

Filament winding

In the filament winding method, a reinforcing material filament is wound over a rotating mandrel layer by layer. High-strength product is achieved in the filament winding process. It is used to produce e-glass, carbon fiber, composite pipes, and others.

The diagrammatical representation of the filament winding method is shown as:

Following are the advantages of the filament winding method:

• Automatic process
• High production rate
• High strength product

Following are the disadvantages of filament winding:

• Poor external surface
• Winding reverse curvatures is difficult

Pultrusion

Pultrusion is a process used to produce high-length composite parts. In this process, the reinforcement fiber material is soaked with resin and extruded through a heated stationary die. The diagrammatical representation of the pultrusion system is shown as:

Following are the various advantages of pultrusion:

• Rapid processing
• Good quality control

Following are the various disadvantages of pultrusion:

• Fiber breakage
• Die jamming

Resin transfer molding

In the resin transfer molding process, a measured quantity of polymer is preheated in a transfer pot and then forced into a preheated mold containing reinforcing fibers. The polymer deforms in the shape of a mold cavity, then after curing, the mold is opened, and desired part is removed.

The diagrammatical representation of resin transfer molding is shown as:

Following are the various advantages of resin transfer molding:

• Low skill labor required
• Low volatile emission

Following are the various disadvantages of resin transfer molding:

• Critical mold design
• Difficult to control resin flow

Autoclave molding

In the autoclave molding process, the molded part is initially placed in a plastic bag from which air is exhausted with the help of a vacuum pump. Heat and inert gas are applied in the autoclave to enable curing and densification of material to develop desired part. It is an expensive process and is used to develop high-quality aerospace products.

Following are the advantages of the autoclave process:

• Very high-quality product
• Produce hybrid composites products

Following are the disadvantages of the autoclave process:

• Costly

Following are the various manufacturing processes used for processing thermoplastic matrix composites:

• Injection molding
• Film stacking
• Diaphragm forming
• Thermoplastic tape laying

Injection molding

Injection molding is a process in which molten thermoplastic mixed with small reinforcing fibers is forced with the help feed screw into a mold cavity with very high pressure. The thermoplastic material in the mold is cooled with the mold's cooling system, and the desired product is removed after solidifying the material.

The diagrammatical representation of injection molding is shown as:

Following are the advantages of the injection molding process:

• Highly productive method.
• Highly accurate
• Mass production

Following are the disadvantages of injection molding:

• Limited product length

Film stacking

In the film stacking process, a stack of polymer films layers with intermediate dry fiber layers is produced with the application of heat and pressure. It is used to produce lightweight and high-strength thermoplastic matrix composites.

The diagrammatical representation of the film stacking process is shown as:

Diaphragm forming

In the diaphragm forming process, sandwiching of freely floating thermoplastic prepreg layers between two diaphragms or silicon sheets are placed in the heated with hot platen up to a specific temperature. After it is placed over forming machine and vacuum is created in the lower site and pressed from the upper site will transform it into the desired shaped product.

The diagrammatical representation of the diaphragm forming process is shown as:

Following are the various advantages of diaphragm forming:

• Produce double curvature components
• Good fiber placement

Following are the various disadvantages of diaphragm forming:

• Long cycle time
• Temperature limitations

Thermoplastic tape laying

In the thermoplastic tape laying method, layers of prepreg tape are applied on the mold surface in the desired position. It is melted by heating with the help of a laser or heating element. It is used to produce airframe components, air cooling ducts, tanks, and many more.

The diagrammatical representation of the thermoplastic tape laying is shown as:

Following are the various advantages of thermoplastic tape laying:

• Automatic machine process
• Less costly

Following are the disadvantages of thermoplastic tape laying:

• Limited to flat or low curvature surfaces

Common Mistakes

Following are the common mistakes performed by students:

• Sometimes, students get confused that chemical linking between individual molecules is present either in thermoset or thermoplastic.
• Sometimes, students get confused as to which processing technique is low volume process.
• Sometimes, students get confused between manufacturing processes used for processing thermoset and thermoplastic matrix composites.
• Sometimes, students forget that diaphragm forming is used for processing thermoplastic matrix composites.

Context and Applications

The topic processing of polymer matrix composites is significant in various courses and professional exams of undergraduate, graduate, postgraduate, doctorate levels. For example:

• Bachelor of Technology in Mechanical Engineering
• Bachelor of Technology in Production Engineering
• Diploma in Mechanical Engineering
• Master of Technology in Production Engineering
• Doctor of Philosophy in Production

Related Concepts

• Polymer
• Manufacturing processes
• Elastomers
• Polymerization

Practice Problems

Q1. Chemical linking is present in _____ polymer matrix composite?

1. Thermoset
2. Thermoplastic
3. Thermoset and thermoplastic
4. None of these

Correct option- (b)

Explanation: Thermoplastic is described as a polymer material made by individual molecules in a linear structure without any chemical linkage between them. The molecular weight of thermoplastic is high, and it is moldable at room temperature.

Q2. Which of the following is not an advantage of filament winding?

1. Automatic process
2. High production rate
3. High strength product
4. Good surface product

Correct option- (d)

Explanation: The main disadvantage of filament winding is poor surface finish of product.

Q3. Which of the following process is used to produce lengthy thermoset parts?

1. Pultrusion
2. Filament winding
3. Diaphragm forming
4. Injection molding

Correct option- (a)

Explanation: The pultrusion is a process used to produce high-length composite parts. In this process, the reinforcement fiber material is soaked with resin and extruded through a heated stationary die.

Q4. In which process, polymer films layers with intermediate dry fiber layers are produced with heat and pressure?

1. Film stacking
2. Diaphragm forming
3. Thermoplastic tape laying
4. None of these

Correct option- (a)

Explanation: In the film stacking process, a stack of polymer films layers with intermediate dry fiber layers is produced with the application of heat and pressure. It is used to produce lightweight and high-strength thermoplastic matrix composites.

Q5. Which of the following thermoplastic method is limited to flat surfaces?

1. Diaphragm forming
2. Injection molding
3. Thermoplastic tape laying
4. Pultrusion

Correct option- (c)

Explanation: In the thermoplastic tape laying method, layers of prepreg tape are applied on the mold surface in the desired position. It is melted by heating with the help of a laser or heating element. It is used to produce airframe components, air cooling ducts, tanks, and many more.