Degradation mechanisms of glass fiber reinforced polymers

Introduction

Polymeric materials have acquired significant importance, thanks to their attractive properties such as lightness, ease of transformation, and design. Despite initial limitations in terms of mechanical strength compared to traditional materials, the study of combinations with fiber reinforcements known as composite materials has broadened their application prospects as an alternative solution in various industries.

Currently, these materials are used in demanding sectors such as aerospace, military, air transport, and construction, covering diverse applications with different levels of specifications and facing environments that can cause deterioration. The evaluation of the mechanical behavior and chemical resistance of fiber-reinforced polymeric materials in various applications is critical, especially in contexts involving prolonged exposure to aggressive environments.

The central purpose of this content is to analyze and understand the degradation mechanisms of glass fiber reinforced polymers (GFRP) when exposed to different chemical agents in the environment. It provides information on how these agents affect the physical and mechanical properties of these materials.

What are Glass Fiber Reinforced Polymers?

Fiber Reinforced Polymers (FRP) are composite materials; constituted by the combination of fibers and a polymeric matrix. Due to their good chemical resistance, these materials are presented as alternative materials in engineering due to the possibility of adjusting their final properties through the selection of their individual components, fiber and matrix, and the processing technique.

The fibers of composite materials: They are responsible for providing the structural properties to the composite material because their stiffness and strength are superior to that of the matrix. Among the most commonly used fibers are glass fiber (GFRP), aramid fiber (AFRP) and carbon fiber (CFRP).

• Glass fibers (GFRP): their main advantage is their low cost, however, they are less resistant than other types of fibers.
• Aramid fibers (AFRP): They show good behavior under cyclic loading and high toughness. They have an anisotropic structure (higher strength and modulus of elasticity in the longitudinal direction), linear elastic response in tension and non-linear behavior in compression.
• Carbon fibers (CFRP): They are the most known and used because they have better mechanical properties than the previous ones, they are manufactured with PITCH or PAN type polymers. PITCH fibers are made of refined petroleum or pitch, while PAN fibers are made of polyacrylonitrile. Both give the materials high strength and elasticity.

The matrix of a composite material: It protects the fibers against abrasion and environmental corrosion, holds the fibers together, and distributes the load between them. It can be thermosetting, the most common type, or thermoplastic, which, when heated, become irreversibly insoluble solids, while thermoplastics behave like liquids when heated.

The most commonly used types of matrices are polyester, vinylester and epoxy resins. These polymers are of the thermosetting type, of high chemical resistance, and easy to process. Epoxy resins have better mechanical properties than polyester and vinylester and high durability.

The following video shows the production process of GFRP manufactured by ONE WORLD is mainly used for the non-metallic reinforcement of ADSS fiber optic cable.

GFRP (Glass Fiber Reinforced Polymer) Production Process.

Degradation mechanisms in glass fiber polymers

Degradation of glass fiber reinforced polymers can occur due to different agents. The main types of degradation are described below:

Thermo oxidative degradation

Thermo-oxidative degradation is a process in which polymers oxidize due to exposure to oxygen and heat. This process is particularly slow at room temperature, but accelerates with increasing temperature and the presence of free radicals. The thermal history of the material and the manufacturing process significantly influence the rate of production of these radicals. Oxidation occurs through a chain mechanism involving initiation, propagation and termination, being an autocatalytic process where the free radicals formed attack multiple polymer chains.

Biodegradation

This process occurs when polymers are attacked by biological agents, such as microorganisms that generate enzymes capable of breaking polymer chains. Although synthetic polymers are usually bioresistant due to the difficulty of finding endpoints for enzymatic attack, materials susceptible to hydrolysis, such as polyesters and aliphatic polyamides, are more prone to biodegradation. Natural fiber reinforcements can also undergo biodegradation, which has led to the search for polymers specifically designed to be biodegradable, with applications in medicine, agriculture and packaging.

Thermal degradation

This type of degradation with temperature involves the breaking of molecular chains at high temperatures, which can generate gaseous species and weight loss of the material. The thermal stability of polymers is related to the bond energies between their constituent atoms, with polymers with higher bond energies being more thermally stable. Pyrolysis, a form of thermal degradation in an inert environment, is another important aspect in the evaluation of the thermal stability of polymers.

Photodegradation

This mechanism occurs when polymers are exposed to ultraviolet radiation in the presence of oxygen. This process can modify the mechanical properties of polymers through the formation of free radicals generated by photon absorption. The effects of photodegradation include the formation of cracks and bubbles on the surface, increased brittleness, color changes, increased electrical conductivity and decreased mechanical properties.

Chemical degradation due to the environment

This type of mechanism is related to the effect produced by the medium with which they interact, producing changes in the properties of the particular components, it is important when designing these materials to consider the application in terms of the medium to which they will be exposed because they can affect the chemical resistance. The following are some types of degradation due to the effects of chemical compounds.

• Degradation in neutral environments: Water, when absorbed by polymers, causes changes in their physical and mechanical properties. Glass fiber reinforced polymers (GFRP) used in wet or aqueous environments (rain, spray, seawater) can have a long service life if properly designed. However, contact with neutral aqueous solutions can adversely affect the properties of reinforced thermoset composites.
• Degradation in alkaline environments: Alkaline solutions can severely degrade the glass fiber, resin matrix and interface, even at low concentrations. In civil engineering, GFRPs in contact with concrete (high pH) require studies to determine their durability. These materials are also used in the chemical industry, where it is crucial to predict their behavior in contact with alkaline solutions.
• Degradation in acidic environments: Acidic solutions significantly affect GFRPs, used in refineries, pulp and paper production, and gas scrubbing systems. Vinylester resins are used in applications requiring resistance to corrosive environments, evaluating their resistance to strong acids such as sulfuric, hydrochloric and nitric.
• Degradation in organic media: Composite tanks in the oil industry are designed to withstand up to 30 years, but can present problems if not properly protected. Polyester composites have poor resistance to non-aqueous media, such as gasoline and diesel, showing significant losses in strength and stiffness after prolonged exposure.

Fiberglass reinforced polymers applications

Glass fiber reinforced polymers (GFRP) have applications in different industries due to their lightweight, mechanical strength and durability properties.

In the aerospace industry, GFRP is used in the manufacture of aircraft components such as fuselages, wings and interior parts. Their high strength-to-weight ratio and corrosion resistance make them ideal for this industry, where every gram counts and durability is crucial. In the automotive sector, GFRPs are used to produce parts such as bumpers, body panels, and structural components. These materials help reduce vehicle weight, improving fuel efficiency and reducing carbon emissions.

GFRP is used in the construction of bridges, buildings and marine structures. Their corrosion resistance and durability in aggressive environments such as salt water make them superior to traditional materials such as steel. In shipbuilding, GFRPs are essential for manufacturing ship hulls and other structures subjected to harsh marine environments. They offer excellent corrosion resistance and reduced maintenance compared to conventional materials.

In the wind energy sector, GFRP is used to build wind turbine blades. Their light weight and strength allow longer and more efficient blades to be manufactured, contributing to increased renewable energy generation. In the chemical industry, GFRPs are used to manufacture storage tanks, piping and other equipment that must withstand corrosive environments. Their chemical and mechanical resistance makes them ideal for these applications.

The following video shows the manufacturing process of polymer tanks with fiberglass. Source: Mega Process.

Process of making glass fiber reinforced plastic storage tank. Korean plastic manufacturing factory.

Conclusions

The degradation mechanisms of glass fiber polymers vary depending on the agents involved. Understanding these processes is crucial to improve the durability and performance of polymeric materials in various industrial and environmental applications.

It is essential to perform durability and resistance studies, different environments to predict the behavior of materials and ensure their effectiveness in industrial applications, such as construction, chemical and civil industries.

References

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