Fibreglass Linings: Polyester and Vinyl Ester
The term ‘fibreglass’ is broadly used to define composite materials made from resin and some form of glass fibre reinforcement. It is also referred to as ‘GRP’, short for glass-reinforced polyester/polymer. elsewhere, the term ‘fibre-reinforced polymer (FRP)’ may also be used – particularly in the United States.
It is a composite with a matrix phase (resin) and a reinforcement phase (matting). A major benefit of fibreglass is that both the type of resin and type of matting used can be selected for specific applications.
It is a slight misconception that one size fits all; the composition (namely the resin and reinforcement types) of the fibreglass covering are often adjusted for more specific applications.
In standard applications such as water storage tank linings, ‘fibreglass’ may comprise polyester resin and E-glass fibre with a polyester topcoat. For chemical bund linings, it usually comprises more bespoke ingredients, such as vinyl ester resin, C-glass reinforcement, a chemically resistant veil and a vinyl ester topcoat. The latter form delivers greater chemical resistance and a higher level of durability – key features for harsh industrial processing environments.
Studies have shown that the resin system has a greater impact in fatigue modes for both polyester and vinyl ester laminates.
Polyester Fireglass (GRP) Linings
Polyester resin is a polymer produced from a polycondensation reaction. Utilised in an unsaturated form, it is often combined with E-glass fibre matting to create a durable and water-resistant composite. In such instances, the mechanical properties are significantly enhanced, transforming the otherwise brittle resin into a highly durable laminate with a degree of flexibility.
Vinyl Ester Fireglass (GRP) Linings
Vinyl ester resins (VER) are a polyester resin sub-class. They undergo a modification step to increase chemical resistance and enhance mechanical properties, albeit at the expense of higher cost and lower storage lifetimes. Many chemical and material engineers see vinyl ester as a bridge between polyester and epoxies.
Unlike standard polyesters, vinyl esters exhibit less shrinkage during the curing process, making them more favourable for substrate coverage. These composites also demonstrate more favorable mechanical properties than polyester, so they are able to better absorb impact without incurring damage or stress-induced cracking. Indeed, a tensile fatigue study between polyester and vinyl ester laminated showed that vinyl ester had a higher average strength and near identical modulus of elasticity.
Applications of Fibreglass Linings
There are a broad range of applications of fibreglass linings and coatings. These range from simple pond and water feature linings to more industrially-targeted projects.
Indeed, both polyester and vinyl ester fibreglass composites are cited as industry standard forms of surface lining for above-ground storage tanks (ABT), bund linings and other forms of primary and secondary containment.
Offering enhanced forms of concrete, steel and other material protection, they significantly extend the lifetime of the underlying structure and in the context of primary and secondary containment requirements, ensure full compliance.
However, the performance of both resin types can vary considerably, so it is important to select the best resin type. This is dependent on the working environment – factors such as reactivity to certain chemicals and overall response to abrasion and impact – all of which can degrade the lining and lead to a loss of integrity.
When used correctly, both types of lining systems are highly durable and resistant to degradation. They serve to protect brittle and permeable surfaces like concrete.
But what is lining degradation?
Degradation
Degradation refers to the response of a material to process when it is exposed to an environment and workload that leads to a reduction in its original properties.
Generally, macromolecule cleavage is a critical step in polymer degradation. Therefore, in a narrower sense, the very process of cleaving macromolecules into fragments of various structures and sizes is often referred to as polymer degradation.
Polymer degradation is accelerated by atmospheric oxygen, high temperature, osmosis, hydrolysis associated with a humid atmosphere, light with a wavelength (>300 nm), biological attack, mechanical stress, contact with aggressive liquids and UV radiation, amongst other factors dicsussed
Therefore, it makes sense to consider the degradation conditions for such composites in their intended working environment.
Fibreglass composites are less resistant to degradation than paints and other resins. They combine strength, flexibility, impact and abrasion resistance as well as chemical and water resistance.
Water Resistance
Water resistance refers to the ability of a material to resist degradation by exposure to water molecules over short- and long-term periods. In terms of polymer coatings and linings, it is illustrated by the ability of the material to repel water molecules, thereby preventing them from entering into the cross-linked nature of the material.
Water resistance is measured in compliance with ISO 1521:1973 (Paints and varnishes — Determination of resistance to water — Water immersion method).
Vinyl esters are more resistant to water-induced degradation than polyesters. This is attributed to the greater hydrophilicity of polyester and its propensity to absorb water. This phenomenon is caused by the entry of water molecules into the polymer network, which accelerates the degradation process.
Due to the low compactness of the polymeric network and the greater hydrophilicity, the latter resin absorbed a higher amount of water. The polystyrene chains leave a high amount of free volume between themselves during the crosslinking reaction with the polyester chains, so this aspect reduces the bulk compactness. Their greater hydrophilicity is caused by the penetration of water molecules into its polymer network, which enables an easier degradation process. Moreover, the ester groups present in the UPRs are responsible for the degradation.
In the case of vinyl ester resin, water detaches the surface layers of material without penetrating into the polymeric network. Vinyl ester possesses fewer open sites on its chain, making it have more resistance to hydrolysis during water penetration and associated osmotic bubble formation.
Chemical Resistance
Chemical resistance is a critical feature in material science. It refers to the ability of a lining and coating material to withstand chemical attack in the form of reactive interactions without undergoing degradation, thereby remaining inert.
It helps the material avoid or delay degradation, enabling the extended protection of the underlying substrate. Chemical resistance is a critical part of any secondary containment system and something fibreglass composites respond well to.
The chemical resistance of a material or surface can be determined in compliance with ISO 2812 Paints and varnishes – Determination of resistance to liquids – Part 1: Immersion in liquids other than water.
Other lining instances requiring waterproofing but limited (if any) exposure to chemicals can utilise standard polyester resin-based fibreglass systems, as shown below for a hospital MRI room.
The table below shows some of the performance of polyester resins in industrial lining uses.
| Application | Environment | Resin | Service Location | Service Temp (oC) | Comments |
|---|---|---|---|---|---|
| Tank Lining | Diesel Fuel | DIONⓇ 6631 | Standard Oil of California | Ambient | Tank life 11 - 15 years |
| Tank Lining | Crude Oil | DIONⓇ 6631 | Conoco/Standard Oil of California | Ambient | |
| Tank Lining | Heavy Fuel | DIONⓇ 6694 | Standard Oil of California | ||
| Steel Tank Overwrap | Motor Fuels | DIONⓇ 6631 | International | Ambient | Single wall and double wall UL listed tanks |
| Settling Tank | Kerosene/5% Sodium Hypochlorite | DIONⓇ 6694 | Standard Oil of California | - | Mild caustic and kerosene separation. Replaced epoxy tank which failed. |
| Settling Tank | Naptha, Aromatics & H2S | DIONⓇ 6694 | Standard Oil of California | 50 oC | Removal and containment of aromatics entrained in hydrogen sulfate |
| Tank Lining | Perco Sweeteners | DIONⓇ 6631 | Conoco/Standard Oil of California | Ambient | Straight run gasoline percolated through 2m x 6.1m steel FRP columns |
Note: data adapted from DION® Polyester Resins. Reichold Chemical Company, Research Triangle Park, North Carolina, September 2010.
Vinyl Ester Resin
On the other hand, vinyl esters have greater chemical resistance owing to the inherent properties of vinyl ester as well as the modified derivatives available. This is because they have superior chemical and hydrolytic stability versus to polyesters; the unsaturated C=C double bonds at the end of the molecular chain are readily available during the cross-linking process.
In addition to demonstrating resistance to fuel-based products, acids, alkalis and other bespoke chemicals require similar containment systems, as the video shows below for a vinyl ester secondary containment lining.
Mechanical Properties
The behaviour of fibreglass laminates is dependent on the ingredients used. The table below shows some of the mechanical properties of fibreglass composites made from vinyl ester and polyester resin. It is notable that vinyl ester has a higher strength than polyester.
Generally, polyester is a preferred resin when cost is a major factor. Conversely, other hand, the static mechanical performance of vinyl ester composites (as seen in the table below via a higher strength) is superior to polyester composites.
| Polyester Fibreglass Laminate | Vinyl Ester Fibreglass Laminate | |
|---|---|---|
| Strength (MPa) | 484 ± 19.6 | 524 ± 28.2 |
| Modulus of Elasticity (GPa) | 20 ± 1.4 | 19.5 ± 0.7 |
Fire Resistance / Flame Retardancy
Flame retardancy is an important part of many primary and secondary containment linings. It is a requirement for COMAH compliant sites.
Unmodified polyester and vinyl ester resins are fundamentally flammable, presenting limits to their industrial usage. As such, efforts have been made to render such resins flame retardant.
Polyester resin and vinyl ester flame retardant versions are available. Both resin systems incur some minor loss of mechanical properties with a slight addition in cost. These downsides are relatively limited in relation to the overall performance of the system.
Recycling, Regeneration and Disposal
The lifetime of a fibreglass lining that operates within specification can extend to well over a decade. However, damaged sections, such as those subjected to excessive impact, frequent and severe abrasion or those exposed to harsh chemicals are amenable to repair. In such instances, the damaged section can be removed, the residual lining abraided back and a new lining applied.
Fibreglass water tanks, for instance, can be repaired and refurbished through the application of a new layer of fibreglass, as the following video illustrates.
Even though small, thin quantities of fibreglass materials are used, at the end of their lifecycle such materials should ideally be recycled. There is currently limited infrastructure for this, but it is expected to change in the coming years – particularly as recycled polyester, for instance, can be more cost-effective than standard resin. As such, cost-effective, efficient and environmentally friendly methods of recycling are being studied and piloted.
Do You Require a Fibreglass Lining?
At Strandek, we’ve been specialising in fibreglass-based systems since 1976. Since then we’ve tackled a range of projects, from industrial lining systems for secondary containment to more general waterproofing for construction projects.
Want to find out more about our services? Call us on 01633 250652 or send us an email.