(Image credits: WFB/Raveling)
The waste generated by the manufacture of FRPs and the entire product cycle can be often as harmful as the raw materials. In progressed countries like the USA, even the organizations that legally and properly disposed of the hazardous waste in the past – in accordance with the prevailing regulations – are now asked to absorb the clean-up cost of these materials.
In many countries, lawsuits have forced companies to pay the cost of removing their wastes from licensed landfills. Given the gravity of this situation, the best approach to limiting the long-term liability is to avoid generating hazardous waste. However, in the FRP industry, this is not likely to happen. The strategy, therefore, should focus on reducing the volume of waste and implementing good manufacturing practices.
The Way Forward
In order to start the change process which is quite crucial, one must first establish the current status of the problem e.g. tons of VOC emission per year, a cubic meter of waste generated or sent to landfill, cost of scrap, etc. as well as the proposed goal. One must also quantitatively know the source of pollution and waste. The styrene lost to the atmosphere, for example, can be estimated from the following table.
This is how a simple change over from regular resin to low styrene emission resin can reduce styrene emission by as much as 60%. Some states in the USA do not permit the use of resins with styrene content greater than 35%.
DCPD based resins tend to be more expensive than conventional resins due to the higher cost of formulation but they offer several other advantages to the molder, for example, higher filler loading, better finish, improved electrical and thermal properties, etc. Achieving good secondary bonding can also be a problem with some reduced styrene resins.
This is in part because the low styrene resins are less forgiving to dust and contaminants on the laminate surface and wax additives used in the majority of the formulations can interfere with the interlayer bonding if proper surface preparation is not done. This makes it important to know the chemistry of the resin to take the fullest advantage of its properties. In spite of these limitations, low styrene emission resins can be a welcome change.
Similarly, benzoyl peroxide (BPO)catalyst has been reported to have a beneficial effect in suppressing styrene emission. This is attributed to a reduction in gel time and a lower peak exotherm with this catalyst system. BPO is typically used with an amine accelerator.
UV curing resin is another good development in this direction. These resins cure on exposure to light and do not require mixing with catalyst or promoters. Evaporation of styrene is reduced because cure starts at the surface and the laminate is sealed from the outside in. Cleaning cost is also lower since the material will not cure on tools.
The disadvantage is that the resin can not be pigmented and only transparent fillers can be added. The geometry of the part may also pose limitations.
Impact of Manufacturing Technologies and Methods
Manufacturing technologies and methods can also play a major role in FRP waste reduction. The conventional spraying and hand lay-up techniques using open moulds may have the lowest tooling and equipment cost but because of the high atomizing air pressure used during gel coat spraying and longer gel time of resin used for open moulding, the waste and scrap costs are very high. Also, open moulding carries a high per piece cost due to the labour-intensive method inherent to the process and limited output. The cost of environmental control can also be high.
On the other hand, Resin Transfer Moulding (RTM) has a high tooling and equipment cost but it practically eliminates the requirement of atomization of resin and gel coat resulting in greatly reduced pollution output. The quality and productivity are also improved.
There is virtually no wastage of resin and styrene loss is eliminated due to closed mould configuration. Even dusts producing secondary grinding operations are reduced because the close moulding system eliminates most flash removal and edge-smoothing requirements. And in spite of the high initial cost, RTM is well suited if the company seeks production volumes of 500-10,000 parts per year of small to midsize components.
For intermediate volumes, vacuum bag moulding may be the best bet. The tooling and equipment cost is low and payback potential is high especially if production rates are moderate and high strength-high quality mouldings are desired. Styrene emission is greatly reduced since only the gel coat is sprayed and the resin cures in a closed mould. Also, the labour cost is low.
Alternatives to Acetone
Given the health hazards and the rising cost of acetone, alternative solvent systems should be considered for cleaning tools and hands of employees. There are two groups of materials that have emerged as an effective alternative to acetone.
The first group consists of high flash point solvents such as diacetone alcohol and propylene carbonate which have much lower vapor pressure and are, therefore, less polluting. They also significantly reduce the risk of fire when compared to acetone. These solvents are more expensive but because they are less volatile, they have a longer usable life and most of them can be effectively recycled.
The second group consists of water-based resin emulsifiers or detergent cleaners. These materials are good for washing hand tools, brushes, and equipment. To use these cleaners effectively, one must provide wash tanks (preferably heated ones) and fixtures to facilitate soaking and scrubbing of soaking and scrubbing of tools. Once the tools are cleaned they can be given a final rinse with acetone in a separate vessel. Detergent-based putties are also available for cleaning hands.
Recycling of solvents
A filtering screen should be placed in the inlet of the collection system to separate solids and sludge. The contaminated solvent can then be sent for recycling, which can help concentrate waste. The recycled solvent can be returned for reuse.
One way to control waste is to have tight control on the quality of raw materials especially the resin and gel coat. The laminator, therefore, must know beforehand, if the resin and gel coats are going to perform in an expected manner.
A performance test of the material must be conducted on receipt and periodically over time if the resin or gel coat batch is not used up in two weeks. This can also lead to substantial savings as the scrap is reduced and productivity is improved
Isolated spray area
Even the most advanced spray systems produce some overspray and styrene vapours and constitute one of the largest sources of pollution as it makes the surroundings unfit for any other activity.
As a first step in controlling pollution, spraying in large open structures should be totally avoided. An isolated spray-up area will not only prevent contamination of air throughout the entire facility but also would avoid contamination of FRP parts by other operations in the plant producing better quality mouldings.
It is generally assumed that because of the specific gravity of a contaminant, it would either rise or fall of its own weight. In practice, this does not happen and even relatively heavy dust particles and vapours are truly airborne and are not subject to any appreciable migration up or down because of their own weight. This is because the contaminant-air mixture is usually overwhelmingly composed of air.
Therefore, the exhaust fans or outlets should be located at or below the operator level. They will then tend to pull the contaminants down and away from breathing level.
Also, it is preferred that the contaminant-producing process or equipment be located between the operator and the exhaust outlet. This will pull the contaminants away from the operator area. One can also consider using a push-pull system in which the contaminants are directed toward the exhaust outlet by a low-velocity air stream produced by fans. Partitions, lowered ceilings, etc. can be used to advantage to enclose the contaminating process as much as possible. The more complete the enclosure, the more efficiently the exhaust system will evacuate the contaminants.
For some applications, the most effective method of evacuating a hazardous airborne substance from the workplace is to use a truly localized exhaust system. This consists of a ducted hood and an exhaust fan. It offers optimum contamination control and minimum air volume requirement and therefore lower cost.
Switching over to non-atomizing gel coat guns can further improve the transfer efficiency of gel coats by approx. 10% especially if it is to be coupled with a controlled application temperature.
There is also growing concerned about how to recycle the gelled resin, trimmings, and old FRP waste. Several US patents have appeared in the past 10 years on the recycling of gelled resin, but the technology is still not well developed for commercial usage.
Recycling FRP trimmings and old FRP waste is also a major concern. USP 5,879,601 and 5,036,788 discuss recycling of FRP waste.
It comprises shredding the composite material into small pieces of 2-8 inches in size and choosing a suitable aggregate granular material with granule size between 1/8 to 1⁄2 inch.
The said aggregate granule and shredded FRP pieces are then mixed with a binder GP resin and cast to produce useful composite products such as waste containers, patio slabs, manhole covers, lamp poles, panels, etc.
Go With Sustainable Manufacturers
Crest’s range of FRP resins has an excellent track record replete with success stories in highly corrosive environments in some of the biggest chemical process industries in India and abroad. If you would like any more information about our custom range of FRP resins and other capabilities, contact us now and a representative will reach out to you for premium resin solutions for your needs.