In the January, 2003 edition of Composites Fabrication Magazine, under the heading Real Dreams: What We Want! 2003 Composites Industry Wish List, author Bob Lacovara said this:
"The trends in technology we have seen across the industry will become magnified as the need for advancement becomes clarified. The 2003 Composites Wish List is a blend of what we need, speculation, and commentary on our present condition. With the understanding that status quo is not an option, envision how these wish list items can impact your operation." (emphasis supplied throughout)
He then went on to detail a range of areas where he felt the industry is in need of significant improvement. Here is a brief summary of some of the major issues he raises.
Top of the list is Composites Processing and Manufacturing Facilities.
The Industry needs "Wider use of enhanced process monitoring. In the traditional open molding process, too much of the final outcome is predicated on the skill and attention of the operator." Real-time monitoring systems can observe the multiplicity of factors inherent in GRP production processes. "Material flow is translated into product thickness- a major quality and cost issue...We need to begin a conversion of open molding from a touchy-feely, operator-dependent process to one of metrics and data control."
As part of this control, the industry needs the Adoption of controlled spraying for all open mold applications. This relates not only to emissions, but to enhancing the work environment, improving quality and reducing costs.
He would also like to Take a rational look at low cost molding methods. Particularly in the closed molding area, where 'proprietary' methods seem to be limiting rather than enhancing growth.
Finally, The industry needs better work conditions. Here he addresses the issue of retaining quality employees in the usually unpleasant work environment of a GRP production facility. "Employers have the means to change this if they have a vision of what can be done to improve shop conditions...ask the question, 'Who would want to work in my shop environment?' If you don't like the honest answer, maybe its time for a cultural revolution!" Second on the list are the development of new Composite Materials. In particular he would like a gel coat "not sensitive to mil thickness... that can be applied at 40 mils thick without cracking, yellowing or producing porosity...Maybe we need to assign the project to a group of naive young chemists who don't know you can't do that."Similarly, he would like to see the Development of low shrink and exotherm controlled resins. "When producing cosmetic parts, the the whole production process is built around dealing with surface distortion caused by resin shrinkage...We have to design the substrate laminate with reinforcements that reduce print-out... The benefit of such a material would be millions of dollars of savings in production costs... The wish list includes resins where the entire laminate is applied in one step and part cosmetics will look great."
Mr. Lacovara goes on to list other needs of the industry. There is need for relief in the Insurance Crisis. Some of these aspects can be addressed by changes in work culture.
Under the general heading of Composites Industry Growth, Lacovara refers to the general reluctance of Engineers to specify composite materials because there are inconsistencies in performance. Composite use in Infrastructure will grow as engineers understand composites better.
Regulatory Issues deal specifically with styrene emissions and the regulation by the environmental authorities.
It is the intention of this paper to show that Polymerisable Liquid Composites can and will address most of the issues on the Composite Industry's Wish List.
Current practice requires placing fibreglass reinforcement onto a mould and then wetting the fibreglass with a resin. The resin does not naturally mix with the fibreglass, it needs to be forced into the fibreglass by mechanical means. The mechanical mixing of the reinforcement and resin requires considerable time and effort and is called rolling out, consolidating the laminate.
Today most fibre reinforcing is sprayed onto a mould as chopped rovings. The spraying of fibres means that some fibres inevitably escape as air-born fibres creating a potential health risk. There is considerable wastage of resin and fibre reinforcement during the spraying process. The fibre chopper motors used for making the chopped rovings require constant maintenance and use considerable compressed air to operate. The requirements for compressed air would be effectively halved if chopper motors were not required.
In Resin Injection Moulding the reinforcement is placed into the mould and is called a preform. The mould is then closed and the resin is pumped in. The preform reinforcing impedes the flow of resin in the mould and requires considerable pressure.
These high pressures make mould manufacture expensive and tend to limit the size of moulds used in RIM processes. This is unfortunate because Resin Injection Moulding is a closed moulding procedure and therefore there are no emissions of Volatile Organic Compounds such as styrene and other monomers and peroxide curing agents.
The whole process of fibreglass fabrication would be vastly simplified if there was no need for fibre reinforcement to be placed separately on or in the mould prior to applying the liquid resin.
A sprayable, pumpable liquid composite does not require external fibre reinforcement and therefore makes the deposition of fibre reinforced laminates much safer, simpler and faster. In a word, efficient.
Polymerisable Liquid Composites, PLCs, were invented by Peter Hodgson. They are a major advance on Short Fibre Composites or SFC's. SFC's have relatively poor physical properties compared with standard fibreglass deposition processes described above.
The reasons for this have to do with the properties of short reinforcing fibres. Simply stated the fibres are too short to carry stresses efficiently.
PLC's use composite fibres and are designed to interact with the curing resin matrix to produce a cured composite with properties similar to standard fibreglass deposition processes. The production of Composite Fibres is not overly difficult. It is the subject of much of the Patent application and so will not be discussed in detail here.
PLC's are at least twice as strong as SFC's, and they have superior impact resistance.
PLC's can be applied using standard fibreglass pump or spray deposition equipment. They are also eminently suited to robotic application. Spraying PLC's is exactly the same as spraying paint. This is a major advance over current methods.
The bulk properties of the cured composite are consistent on both the macro and micro scale, which allows for superior post-curing manipulation of the product, eg, machining to fine tolerances, vastly reduced 'chipping' of edges, etc.
PLC's provide a liquid composite which is entirely new to the FRP marketplace. It can be readily adopted and adapted to existing products and production techniques.
The fact that the composite is easily sprayed or pumped, and has excellent flow characteristics means that it is suitable for a host of novel applications. Repairing structural cracks, repairing concrete cancer, waterproofing, corrosion control, repairing pipe-work, lining pipes, continuous casting of sheet material, moulding machineable castings, are a few examples.
The features and advantages of Liquid Composite Technologies are a fine example of the old saying, "Necessity is the mother of invention." Mr. Peter Hodgson, analytical chemist and inventor of LCT, has had 15 years experience in the Plastics Industry. He observed over that time the problems associated with standard fibreglass deposition and moulding techniques.
Peter Hodgson is regularly engaged by the fibreglass pool industry in Australia as a consultant on failure processes caused by the hydrolytic degradation of permanently immersed fibreglass laminates (Osmosis). He was the first to describe all the contributing factors to these processes in detail. Eg, poor wetting of fibres, air entrapment in fibre bundles, hydrolysis of sizing, hydrolysis of resin matrix etc.
This detailed awareness of the potential problems of current resin/glass composites and deposition processes led him to ask the simple question: "Is there a better way?"
Removing the need to add fibre reinforcement separately from the resin has proved a very difficult task for the FRP industry. Untreated fibre reinforcement, short enough to allow for spray deposition, is too short to support stresses imparted by the matrix.
In PLC's, the resin and composite fibres are in single phase. There is really no interface between the composite fibres and the liquid resin matrix. The composite fibres seem to "dissolve" in the resin.
In the cured composite, the question "How long is the composite reinforcement?" is virtually impossible to answer. All that can be said is that the effective length is many times the actual length, and this is what gives PLC's their superior properties. Simply stated, the short fibres interact with each other strongly and therefore behave as if they were much longer fibres.
Polymerised liquid composite, when cured, has the following properties:
Tensile strength >= 100MPa
Tensile Modulus 3 - 6 GPa
Flexural Strength >= 130MPa
Flexural Modulus 3 - 6GPa
Why quote a range of figures for the results above? This is simply because the properties of the short fibre composite depend on the properties of the base resin used. Oligomers such as urethane acrylates and vinyl functional elastomers can be added to produce composites with enhanced properties.