Composite Without Compromise: Odour Control in GRP, SMC, and FRP Vessel Manufacturing

Proven Strategies to Keep Emissions and Nuisance Odours in Check

1. Introduction

Composite vessels made from FRP, GRP, and SMC are the backbone of many industries—offering unmatched strength, corrosion resistance, and design flexibility. But behind these advanced materials lies a quieter challenge: the odours generated during manufacturing. These emissions, primarily from resin curing and finishing operations, can affect worker health, community relations, and regulatory compliance. In this blog, we explore the sources of odour in composite vessel production and share proven strategies to control them—so manufacturers can deliver high-performance products without compromising air quality or reputation.

2. Understanding the Materials

FRP (Fiber-Reinforced Plastic) refers to a broad category of composites made from a polymer matrix reinforced with fibres such as glass, carbon, or aramid. GRP (Glass-Reinforced Plastic) is a subset of FRP, where the reinforcing fibre is glass. SMC (Sheet Moulding Compound) is a type of pre-impregnated fibre composite, usually consisting of chopped glass fibres and thermoset resins, used in compression moulding. These materials are popular for vessel manufacturing due to their excellent mechanical properties, lightweight nature, and corrosion resistance. However, many of the resins used—particularly polyester and vinyl ester—emit volatile organic compounds (VOCs) like styrene during processing. These emissions are the primary source of odour and present both environmental and health concerns if not properly managed. Let’s first dive into little more details on each material.

A. GRP: Definition and Composition

GRP (Glass Reinforced Plastic) is a composite material composed of glass fibres, such as E-glass or S-glass, embedded in a plastic resin matrix, typically polyester, vinyl ester, or epoxy. The term emphasizes the use of glass fibres as the primary reinforcement, making GRP a specific subset of fibre-reinforced composites. It is widely chosen for its balance of strength, corrosion resistance, and affordability.GRP offers good mechanical strength, excellent corrosion resistance, and moderate stiffness, though it is heavier than carbon-based composites. It is cost-effective and ideal for large structures like storage tanks, pressure vessels, pipes, and marine vessels such as boat hulls. GRP is commonly used in industries like water treatment, air pollution control, chemical storage, oil & gas, and marine applications due to its durability and resistance to harsh environments.

B. SMC: Definition and Composition

SMC (Sheet Moulding Compound) is a composite material made of chopped glass fibres (typically 25-50 mm long) mixed with a thermosetting resin, usually polyester, along with fillers like calcium carbonate and additives. Supplied as mouldable sheets, SMC is designed for compression moulding, enabling the production of complex shapes with consistent thickness and high-quality surface finishes.SMC provides good mechanical strength, dimensional stability, and an excellent surface finish, but its shorter, chopped fibres result in lower strength compared to continuous-fibre composites like GRP for high-load applications. It is well-suited for smaller, intricate components such as covers, enclosures, automotive panels, or small tanks, where high-volume production and aesthetic quality are priorities. SMC is less common for large vessels due to its structural limitations, being that said, many companies have come up with designs with steel supports making the SMC panel tanks suitable for somewhat larger applications as well.

C. FRP: Definition and Composition

FRP (Fiber Reinforced Plastic) is a broad category of composites that includes any type of fibreglass, carbon, aramid, or basalt—embedded in a plastic resin matrix. GRP is a type of FRP when glass fibres are used, but FRP also encompasses high-performance fibres like carbon or aramid. This versatility allows FRP to be tailored for a wide range of applications, from general-purpose to specialized uses.FRP’s properties vary by fibre type: glass-based FRP (like GRP) offers corrosion resistance and moderate strength, carbon-based FRP provides a high strength-to-weight ratio and stiffness, and aramid-based FRP excels in impact resistance. Glass-based FRP is used for tanks and pipes, like GRP, while carbon or aramid-based FRP is employed in aerospace, automotive, high-pressure vessels, and advanced marine structures like aircraft components or high-performance yachts. FRP’s cost ranges from affordable (glass) to expensive (carbon/aramid), depending on the fibre and manufacturing process.

3. Why Odour Control Matters

Odour control in FRP/GRP manufacturing is far more than a matter of comfort—it’s a critical aspect of health, safety, and compliance. The Odours are largely caused by VOCs, such as styrene, a common component in polyester and vinyl ester resins. Prolonged exposure to styrene and similar compounds can lead to respiratory issues, neurological symptoms, and other health problems for workers. Additionally, regulatory agencies worldwide impose strict limits on VOC emissions to safeguard air quality and public health. Non-compliance can result in significant fines and legal challenges. Beyond regulations, persistent Odours can strain relationships with neighbouring residents and businesses, potentially damaging a company’s reputation. Effective Odour management, therefore, is essential for worker well-being, regulatory adherence, and maintaining community goodwill.

4. Odour Issues Specific to Each Material

The manufacturing of GRP (Glass Reinforced Plastic), SMC (Sheet Moulding Compound), and FRP (Fiber Reinforced Plastic) vessels involves processes and materials that can release odorous compounds. The primary sources of odours stem from the resins, solvents, and additives used, as well as specific manufacturing techniques. Below is a detailed breakdown of the odour sources for each material, organized by material type.

A. GRP Vessel Manufacturing: Odour Sources

GRP vessels are made using glass fibres and thermosetting resins (e.g., polyester, vinyl ester, or epoxy) through processes like hand lay-up, filament winding, or resin transfer moulding (RTM). Odour sources include:

(i) Resins (Styrene Emissions):

• Polyester and vinyl ester resins, commonly used in GRP, contain styrene, a volatile organic compound (VOC) with a strong, sweet, and pungent odour. Styrene is released during resin mixing, application, and curing, especially in open-mould processes like hand lay-up or spray-up.
• Epoxy resins, while less odourous than polyester, may still emit mild chemical smells during curing.

(ii) Solvents and Thinners:

• Solvents like acetone or toluene are used to clean tools or thin resins, releasing sharp, chemical odours. These VOCs evaporate quickly, contributing to workplace odours.

(iii) Curing Agents and Catalysts:

• Catalysts like methyl ethyl ketone peroxide (MEKP), used to initiate resin curing, have a strong, acrid odour. Improper handling or mixing can amplify these emissions.

(iv) Open-Mold Processes:

• Processes like hand lay-up or spray-up expose wet resin to air, increasing the release of styrene and other VOCs. These methods are more odour-intensive compared to closed-mould processes like RTM.

(v) Dust and Fumes:

• Cutting or grinding glass fibres during preparation or finishing generates dust with a faint, musty smell. Post-curing trimming or sanding of GRP parts can release resin fumes and fine particulate matter, adding to the odour profile.

B. SMC Vessel Manufacturing: Odour Sources

SMC is a pre-mixed composite of chopped glass fibres, polyester resin, fillers, and additives, moulded into sheets and compression-moulded under heat and pressure. Odour sources are generally less intense than GRP due to the closed-mould process but still significant:

(i) Resins (Styrene and Other VOCs):

• SMC uses polyester resins containing styrene, which emits a pungent odour during the compounding stage when resin is mixed with fibres and fillers. However, since SMC is pre-mixed and stored as sheets, styrene emissions are more controlled compared to GRP open-mould processes.

(ii) Additives and Fillers:

• Additives like low-profile agents (to reduce shrinkage) or thickeners (e.g., magnesium oxide) may release mild chemical odours during mixing or moulding. Fillers like calcium carbonate are odourless but can contribute to dust-related smells.

(iii) Compression Moulding:

• During moulding, heat (typically 120-150°C) is applied, causing residual styrene or other VOCs in the SMC to volatilize, releasing a warm, chemical odour. Closed moulds reduce emissions compared to GRP’s open processes, but some odour escapes during Mould opening.
• Use of mould release agents with distinct chemical odours.

(iv) Solvents for Equipment Cleaning:

• Acetone or other solvents used to clean moulds or tools emit sharp, chemical smells. These are less frequent than in GRP manufacturing but still contribute to odours.

(v) Post-Moulding Finishing:

• Trimming, drilling, or sanding SMC parts can release mild resin fumes and dust with a faint, chemical, or musty odour, especially if the material is not fully cured.

C. FRP Vessel Manufacturing: Odour Sources

FRP encompasses a broad range of composites, as an umbrella category, FRP includes both GRP and SMC, but also other forms like carbon-reinforced or aramid-reinforced plastics, or other fibres, using resins like polyester, vinyl ester, or epoxy. Odour sources depend on the fibre and process but overlap with GRP for glass-based FRP:

(i) Resins (Styrene and Epoxy Emissions):

• For glass-based FRP (equivalent to GRP), styrene from polyester or vinyl ester resins is the primary odour source, with a strong, sweet smell during mixing, application, and curing.
• Epoxy resins, common in carbon or aramid FRP, emit milder, chemical odours during curing, often described as less pungent than styrene but still noticeable.

(ii) Solvents and Cleaning Agents:

• Acetone, toluene, or other solvents used for cleaning tools or preparing surfaces release sharp, chemical odours. These are common across all FRP types, especially in hand lay-up or filament winding.

(iii) Curing Agents:

• Catalysts like MEKP for polyester resins or amines for epoxy resins have strong, acrid odours. Amine-based hardeners in epoxy systems, used for carbon/aramid FRP, can produce ammonia-like smells during curing.

(iv) Manufacturing Processes:

• Open-mould processes (e.g., hand lay-up for glass FRP) release more styrene and VOCs than closed-mould methods (e.g., RTM or autoclave curing for carbon FRP). Autoclave curing, used for high-performance FRP, contains odours better but may still release epoxy fumes when moulds are opened.
• High-temperature curing (e.g., in autoclaves for carbon FRP) can volatilize resin components, producing warm, chemical odours.

(v) Fiber-Specific Odours:

• Glass fibres in FRP generate dust with a musty smell during cutting or sanding, like that of GRP.
• Carbon or aramid fibres produce less dust but may release faint, burnt, or chemical odours during machining or if overheated during curing. These are minimal compared to resin-related odours.

5. Odour Control Strategies

The manufacturing of GRP (Glass Reinforced Plastic), SMC (Sheet Moulding Compound), and FRP (Fiber Reinforced Plastic) vessels involves resins, solvents, and additives that release odourous volatile organic compounds (VOCs), notably styrene from polyester resins. These odours, described as pungent or chemical, can affect worker health, community relations, and regulatory compliance. Effective odour control strategies are essential to mitigate these emissions, improve workplace safety, and adhere to environmental standards. The odour control strategies are categorised into two – process/product specific odour control strategies with respect each product and End of pipe solutions applicable for all the three products. First, we will cover few tailored strategies for each material, focusing on ventilation, material selection, process optimization, and followed by end-of-pipe solutions or advanced filtration methods.

A. GRP Vessel Manufacturing

(i) Ventilation and Air Extraction Systems:

GRP vessel manufacturing frequently employs open-mould techniques such as hand lay-up or spray-up, where styrene-rich polyester resins are exposed to air, resulting in significant VOC emissions. To address this, robust ventilation systems, including local exhaust ventilation (LEV) systems, are critical. These systems are installed at key emission points, such as resin application and curing stations, to capture odorous air. Regular maintenance of these systems prevents resin residue buildup, which could otherwise exacerbate odours, and ensures consistent performance in high-emission environments.

The implementation of ventilation systems not only reduces odours but also enhances workplace safety by minimizing worker exposure to harmful VOCs. For closed-mould processes like resin transfer moulding (RTM), sealing moulds tightly and integrating ventilation at demoulding stages further controls odour escape. These systems can be tailored to facility size, with smaller setups using standalone filtration units and larger plants opting for integrated HVAC solutions.

(ii) Use of Low-Styrene or Alternative Resins:

A proactive approach to odour control in GRP manufacturing involves selecting low-styrene or styrene-free resins to reduce VOC emissions at the source. Traditional polyester resins contain high styrene levels, contributing to strong odours and health risks. Low-styrene polyester resins or vinyl ester resins emit fewer VOCs during curing, significantly decreasing odour intensity. While these resins may increase material costs, they offer long-term benefits, including reduced odour complaints, improved worker safety, and alignment with environmental regulations.

The adoption of alternative resins requires careful consideration of application suitability, as vinyl ester or epoxy resins may have different mechanical properties or curing requirements compared to polyester. Manufacturers must evaluate these factors against the specific needs of GRP vessels, such as corrosion resistance for chemical storage. Pilot testing low-styrene resins can help assess performance without disrupting production. This strategy also supports sustainability goals by reducing the environmental impact of VOCs, making it appealing for facilities aiming to enhance their corporate social responsibility profile.

B. SMC Vessel Manufacturing

(i) Enclosed Mixing and Moulding Processes

SMC manufacturing involves pre-mixing chopped glass fibres with polyester resins and additives to create mouldable sheets, followed by compression moulding in closed systems, which inherently produces fewer odours than GRP’s open-mould processes. To control odours during mixing, enclosed systems with integrated ventilation or extraction units are essential. Automated mixing equipment minimizes styrene release by containing the process, while local exhaust ventilation captures any emissions during material handling. During compression moulding, closed moulds reduce odour escape, but residual styrene may be released when moulds are opened. Installing LEV systems near moulding machines ensures these emissions are captured and treated, maintaining a low-odour environment.

Enclosed processes offer significant advantages, including reduced worker exposure to VOCs and compliance with workplace safety regulations. For facilities producing high volumes of SMC components, such as small tanks or automotive parts, these systems enhance efficiency by streamlining odour control within the production line.

Additionally, Regular cleaning of mixing and moulding equipment prevents resin buildup, which could contribute to persistent odours.

(ii) Post-Curing and Off-Gassing Management

After moulding, SMC vessels may retain residual styrene, leading to odours during storage or use. Post-curing techniques, such as exposing moulded parts to controlled heat in a dedicated chamber, accelerate the off-gassing process, allowing VOCs to be released in a contained environment. This can be achieved using ovens or curing rooms equipped with ventilation systems that direct off-gassed air through and odour control unit (OCU). Alternatively, parts can be stored in well-ventilated off-gassing areas before finishing or packaging, reducing odour levels in the final product.

C. FRP Vessel Manufacturing

(i) Ventilation and Air Extraction Systems:

FRP vessel manufacturing, which includes GRP and other fibres like carbon or aramid, often involves open-mould processes that release significant styrene and other VOCs. Therefore, proper ventilation and air extraction is the key strategy.

(ii) Process Optimization and Enclosure:

Optimizing the manufacturing process for FRP vessels can significantly reduce odour emissions by minimizing solvent use, use of epoxy resins with milder odour and optimising curing times. Selecting faster-curing resins or adjusting formulations to lower styrene content decreases VOC release during production. Enclosing open-mould processes in booths or isolated areas equipped with exhaust systems allows for better control of odorous air, directing it through filtration units before release.

For closed-mould processes like filament winding or pultrusion, ensuring moulds are tightly sealed and equipped with integrated ventilation systems prevents odour escape during curing or demoulding, enhancing overall air quality management. Process enclosures offer dual benefits of odour control and improved production efficiency by reducing material waste and worker exposure to VOCs.

D. End-of-Pipe solutions or Advanced Filtration Systems

Effective odour control combines process optimization, engineering controls, and air treatment technologies. By combining enclosed systems with air treatment, manufacturers can achieve a cleaner workplace and minimize community complaints, particularly in urban settings where facilities are near residential areas.

Advanced air filtration systems are highly effective for removing these compounds from the exhausted air. These filters adsorb styrene and other organic molecules, achieving up to 99.5% reduction in odourous VOCs. Key advanced filtration strategies include:

• Scrubbers:

1. Wet Scrubbers: Use water or chemical solutions to absorb and neutralize VOCs.
2. Dry Scrubbers: Use dry media (e.g., activated alumina or impregnated pellets) to capture specific compounds.

• Activated Carbon Filters: Adsorb VOCs and odorous gases effectively; ideal for point-source or room-scale filtration. Regular monitoring of filter performance and replacement of saturated carbon are necessary to maintain effectiveness.
• Biofiltration Systems: Especially for larger facilities, biofilters offer a sustainable method for treating air streams by using microbial action to degrade odorous compounds. They are effective for low-concentration, high-volume emissions.
• Regenerative thermal oxidizers (RTOs) or catalytic oxidizers: Are also applicable for large facilities having separate streams for high concentration streams. The system can destroy VOCs through high-temperature oxidation, converting them into carbon dioxide and water. These are generally deployed as standalone units near high-emission areas like spray booths or lay-up stations of large facilities.

Employing these systems can mitigate community complaints by preventing odourous emissions from escaping the facility, which is critical for plants located near residential areas. Another factor which is overlooked in many places are the employee training; Ensuring proper storage, mixing, and application techniques minimizes unnecessary emissions. Implementing these changes requires upfront investment in equipment and process redesign, but the resulting reduction in odour complaints, improved public relations and regulatory penalties offsets these costs and justify the investment. Regular process audits and air quality monitoring ensure that optimizations remain effective, allowing manufacturers to adapt to changing production demands or regulatory requirements while maintaining a low-odour environment.

6. Regulatory and Community Considerations

Odour is not just an operational issue—it’s a community and compliance matter. Many jurisdictions have strict odour and VOC regulations. For example, styrene is a listed hazardous air pollutant (HAP) under U.S. EPA regulations. Manufacturers must monitor emissions and often report to local environmental authorities. In regions like the EU, occupational exposure limits (OELs) and industrial emissions directives (IED) govern VOC discharge. Facilities must demonstrate that Best Available Techniques (BAT) are being used for odour control.

Equally important is proactive communication with the community. Transparent environmental practices and prompt response to concerns build trust and social license to operate.

7. What EES Can Do for FRP/GRP Manufacturers

Elixir Enviro Systems Pvt Ltd (EES) offers specialized odour control solutions tailored to the unique challenges of FRP/GRP manufacturing facilities. Our services and technologies help reduce VOC emissions, improve workplace safety, and ensure regulatory compliance.

🔧 Customised Solutions We Offer:

1. Design of Ventilation systems, Enclosure and Containment Solutions

• Design of proper ventilation systems and its installation.
• Design and installation of enclosed curing booths with integrated emission control.
• Modular systems for retrofitting existing facilities.

2. Process Optimisation Consulting

• Transition support for low-VOC or styrene-free resins.
• Guidance on closed-mould systems and curing environment improvements.
• Process audits to identify and reduce emission hotspots.

3. On-site Services

• Odour Assessment & Mapping: Identify sources and odour dispersion patterns.
• VOC Monitoring & Analysis: Using state-of-the-art instruments.
• Preventive Maintenance & Operator Training: To ensure ongoing system performance and compliance.

4. Odour Control Equipment

• Activated Carbon Filters: For capturing VOCs like styrene.
• Biofilters: Use microorganisms to biologically degrade odorous compounds.
• Chemical Scrubbers: For targeted removal of specific VOCs.
• Thermal Oxidizers: High-efficiency systems that destroy VOCs via combustion.

5. Regulatory Compliance Support

• Emission modelling and simulation for statutory reporting.
• Documentation support for local and international environmental standards.

💡 Why Partner with Elixir Enviro?

• Deep domain knowledge in industrial odour and air quality management
• Proven experience in custom-engineered solutions for composite industries
• Commitment to sustainability, worker health, and community welfare
• Responsive after-sales support and service contracts

8. Conclusion

Controlling odour in GRP, SMC, and FRP vessel manufacturing is not just a regulatory necessity—it’s a mark of modern, responsible manufacturing. By combining smarter material choices, better processes, and effective air treatment systems, companies can uphold product quality while protecting the environment and their communities. The result is a cleaner, more sustainable path forward for the composites industry. Partnering with Elixir Enviro Systems ensures access to industry-leading solutions for effective Odour management.