Polymer Matrix Composites

Polymer-matrix composites are increasingly encountered as a widely-used material today. The reason for their frequent use is the superior properties they offer. In this article, which I have prepared by compiling various studies, I have examined the properties of polymer-matrix composite materials, the fields in which they are used, and specifically their use in the automotive industry.

Structure of Composite Materials

Before discussing polymer-matrix composites, it is necessary to examine the structure of composite materials and understand what they are. When we look at composite materials, composites are considered one of the most important members of the advanced materials group. Composites are artificial materials created by combining two or more materials at the macro level while preserving their components in order to combine their properties into a single material. In composite materials, the matrix forms the primary phase. To the primary phase, which does not have all the desired properties on its own, reinforcements are added to create composite materials. In the polymer-matrix composites that we will examine in this research article, the primary phase is polymers. Composite materials generally consist of a primary matrix with low strength and reinforcing materials that strengthen the primary matrix. Reinforcements are utilized to increase the strength of composite materials or add desired properties. The general characteristic of the primary matrix in composite materials is to protect the reinforcements from external factors and keep the entire composite structure together.

Polymers

Looking at polymers, the word polymer has Greek origins and is formed from the combination of the words "poly" and "meros". While "poly" means many, "meros" means part. From the origin of these two words, it can be understood that polymers are long-chain molecules created by linking small molecules together. There are three types of polymers: thermoplastic, thermoset, and elastomer. Synthetic polymers, also known as plastic materials, are widely used today. According to research conducted, 300-400 tons of polymers are produced annually worldwide, and the rate of polymer technology development in developing and developed countries exceeds 10%. The main reason for this is that polymers are low-cost, easily processable, lightweight, and resistant to corrosion and chemical agents.  

Polymer-Matrix Composite Materials

Polymer-matrix composite materials are used in many fields today. An increase in the use of polymer-matrix composites has been observed over the years in parts of land and sea vehicles, paints, construction, packaging, electrical-electronics and other industries. The reason for this increase is the use advantages offered by polymer-matrix composite materials. Due to their positive properties such as durability, impact resistance, flexibility, lightweight, and robustness, polymer-matrix composites are used in many industries. Polymer-matrix composites are divided into two categories. These categories are continuous-fiber composites and particle-filled composites. When we compare these two categories, it is notable that continuous-fiber-containing composites are used more frequently in areas where high performance is required. Continuous-Fiber Composites are created with fine fibers placed in a matrix structure. Fiber-reinforced composite materials are frequently used in industry and have a very wide range of applications. Here, the absence of defects in the fiber structure is quite important for strength, and glass, carbon, kevlar and boron are used as reinforcements.   Particle-Filled Composites are obtained by having particles of one material within another matrix. Here, the durability of the structure is related to the hardness of the particles used.

Structure of Polymer-Matrix Composites

In polymer-matrix composites, thermoset and thermoplastics can be used. In addition to these, glass fiber, carbon fibers, alumina fibers, aramid fibers and boron fibers are used. Among these, the most well-known and most widely used are glass fibers.

Thermoset Polymers

Thermoset polymers are more brittle than thermoplastics and exhibit higher strength. The first polymer-matrix composites were made from thermoset polymers. Composite materials made from thermoset polymers have internal structure sensitivities and therefore can cause undesirable defects in composite products where high performance is expected. The thermoset polymers commonly used in polymer-matrix composites are polyesters, epoxies, vinyl esters, phenolics, polyurethanes, silicones and amino resins.

Thermoplastic Polymers

Thermoplastic consumption represents approximately 80% of all plastic materials. Thermoplastics are increasingly being used in composite materials to improve product performance and reduce costs. Thermoplastic polymers do not require curing and harden naturally when cooled, which reduces costs. For this reason, they are preferred by manufacturers in composite materials, which are generally expensive. At the same time, thermoplastics show high resistance to environmental conditions, chemicals and petroleum derivatives. Since thermoplastic-matrix composites are recyclable, they are increasingly used in various fields. The thermoplastic polymers most frequently used in polymer-matrix composites are polyethylene, polypropylene, polyvinyl chloride, polyamide, polycarbonate and polyacetal. [2]

Manufacturing Methods

For the production of polymer-matrix composites, it is necessary to select appropriate matrix reinforcement and additional materials, and these materials must be properly structured. One of the steps that must be considered most carefully during production is polymerization. Various methods can be used when manufacturing polymer-matrix composites. These methods can be listed as hand lay-up, spray-up, press molding, transfer molding, vacuum molding, cold molding, autoclave molding, filament winding and matrix injection molding. In addition to these methods, other methods also exist.

Use of Polymer-Matrix Composites in the Automotive Industry

The automotive sector is among the industries that benefit from polymer-matrix composites. The automotive sector has generated new requirements through technological changes it has undergone over the years. Today, one of the most frequently discussed issues alongside the climate crisis is the production of more environmentally friendly vehicles. At this point, polymer composites can be utilized. The use of polymer-matrix composites in automobiles has increased compared to previous years. In Turkey, polymer-matrix composites were first used in the carports of Anadol brand cars in the 1960s. Following this, the use of these composite materials in trucks, buses, commercial vehicles and other types of vehicles has shown a steady increase. [3] A large portion of polymer-matrix composite materials used in the automobile industry is made up of thermoplastics. In terms of proportion, in the automotive sector, 50% thermoplastics are used, while 24% thermoset composites are used. The use of composite materials in the automotive industry provides contributions such as: • Lightening the product, • Impact resistance, • Fuel savings, • Low carbon dioxide emissions, • High strength, • Energy absorption, Particularly, the use of polymer-matrix composites is preferred by automotive companies because it reduces vehicle weight. As vehicles become lighter, an increase in speed and performance is observed, while at the same time the reduction in weight produces important results in terms of environmental pollution. Reducing carbon dioxide emissions is a goal that many automotive brands are working on due to the climate crisis. This goal has also increased the use of carbon-fiber-reinforced polymeric composites. Because vehicles with reduced weight produce less carbon emissions. At the same time, the use of glass-fiber-reinforced composite materials also creates a cost advantage for automotive companies. In recent years, manufacturers are also utilizing polymer-matrix composites to provide interior noise insulation. Manufacturers who turn to polymer-matrix composite sandwiches for sound insulation achieve the desired results. Due to the mentioned properties, polymer-matrix composites are used both in the automotive industry and in many other industries. With the correct reinforcements added to composite materials whose primary phase consists of polymers, flexible, durable and resistant materials are obtained. Polymer technology, which develops in line with technological advances, allows for the achievement of more advanced composites.     References: 1- Polymer-Matrix Composite Materials Used in the Automotive Industry, Saffet Gülmez. 2- The Importance and Future of Polymer-Matrix Composites in Industrial Product Design, Murat Sönmez. 3- Internal Structure of Particle Material in Polymer-Matrix Composites, Senior Engineer Onur Çoban.   Prepared by: Nilsu Kotil