Facts about Styrene Exposure
Styrene, a chemical used in the manufacture of composite parts made of polyester and vinylester, has been getting a bad name as of late. There has been much debate as to how carcinogenic this chemical is to humans.
From the video description:
This video is part of ACMA’s Risk Communication Program. ACMA’s Risk Communication Program is designed to give owners and managers the tools they need to inform and reassure their employees and plant neighbors about chemical health risks.
The ACMA is the American Composites Manufacturer’s Association is the world’s largest trade organization serving the composites industry.
Styrene is an important component of many products used in the world around us to make strong, lightweight, composite materials. There are many wonderful uses of this chemical and it is an important ingredient in many raw materials. It can be safely used with proper precautions to protect human health.
Moldless Car Body
Building a custom car body with fiberglass can be achieved without using a mold! This will be a truly custom, unique vehicle. It will take lots of planning and hands-on work, but is very possible as shown in these YouTube videos.
There of course are several ways to go about building a basic structure to use for the basic shape. This video gave lots of good ideas and examples of materials that are relatively inexpensive.
The second part of the video shows some of the actual fiberglass work. This video of less than eight minutes does not nearly do justice to the amount of work and effort that went into finishing this project! It was great that the author documented his work and shared with all. This was a major project that is not for the faint of heart.
He does a very good job explaining the process and materials used in this construction. Every project is unique, however. When discussing the thickness of the fiberglass skin, there are many variables that determine the finished strength. The number of layers to use is dependent on the amount of underlying support structures, part geometry, and required load bearing capacity of the structure. Some areas may need to be stronger for impact resistance and structural loads.
The video author discusses only using epoxy resin with Styrofoam as opposed to polyester resin which will react with the Styrofoam. Polyester resin can be used if separated from the Styrofoam with an additional layer. While I have only seen it advertised, there are new spray on primer materials available to cover the Styrofoam and allow polyester resins to be utilized afterward.
Working with Bondo
Commonly referred to by the trade name of “Bondo,” polyester body filler is used by autobody shops to achieve cosmetic repairs on automobiles. It is relatively inexpensive, easy to work with, and achieves good results when used properly. It is basically polyester resin that is highly filled to create a thick paste which can be turned into a solid with the addtion of a hardener.
I have been using autobody filler since age 14, and am finally getting good at it! Just kidding. It is more art than science, and practice makes perfect. Basically, a surface needs to be properly prepared to achieve good adhesion. Then the filler is applied after being mixed with hardener, and allowed to cure afterwords. Some fillers can be sanded as soon as 20 minutes after application.
Basic setup and tools
The basic setup is a working board surface to mix the bondo and hardener. The mixed material is applied with a squeegee or putty knife to fill in low areas. They also aid in cleanup, along with some paint thinner to clean the tools.
Hardener added
Mixing the hardener starts the application window from where the material goes from liquid to solid. The hardener is a peroxide paste that directly affects cure time along with temperature. Too little hardener can also cause poor physical strength characteristics along with difficult sanding properties.
Uniformly mixed
The hardener must be uniformly mixed before it is applied. This prevents lots of problems down the road.
Applied to surface
The body filler can be applied with putty knives or squeegees to achieve the desired affect. This polyester bodyfiller will shrink during cure, so filling high is typical. The flip side is that all of the high spots must be sanded back down, which is wasting filler and time, so it is a fine line to walk.
Working with body filler can be frustrating for the beginner who must practice lots of patience. There are many important aspects that must be followed, just like all composites materials processes. Autobody filler requires proper surface preparation, mixing and metering of materials, and attention to details in order to avoid future problems.
A couple of other practices I recommend is to always wear a dust mask, keep the body filler dry, and only apply bondo over sanded bondo. Some like to just build layers without sanding the lows, and this can lead to adhesion problems.
Liquid now, Hard later
Most of the traditional Thermoset Unsaturated Polyesters, Thermoset Unsaturated Vinylesters, and Epoxies arrive at the fabrication shop as liquids in buckets, drums, totes, or tankers. They require liquid hardeners to be mixed in at specific ratios in order to transform into a solid physical state. The esters use peroxide catalysts in the 1% to 3% range, and the epoxies use a specifically formulated part B designed in tandem with the part A manufacturer. The esters also can come prepromoted or unpromoted, which basically is another part of the chemistry package typically containing a cobalt-based mixture that promotes the curing process. Where this is added depends upon several variables, and can also affect the shelflife of the product.
Nontraditionally the Epoxies and esters can come into the fabrication shop as prepregs. These are resin and glass mixtures that are formable to shape but have all of the chemicals and glass mixed in, and are activated by heat (ovens). This of course requires that they be transported and stored in refrigerated containers. There are several tradoffs for prepregs including cost, delivery, process control, shelflife, etc.
The Different Polyester Resins
Polyester Resins can be further defined by their chemistry. These categories are described as Orthophthalic (Ortho), Isophthalic (Iso), Dicyclopentadiene (DCPD). Vinylesters have a unique chemistry and that shares many working properties with the polyesters.
Orthophthalic (Ortho) resins are based upon orthophthalic acid and are a good basic, general-purpose, inexpensive resin. They have styrene content between 35% and 45%, and are used in applications that do not require elevated service temperatures, high corrosion resistance, or high mechanical properties.
Isophthalic (Iso) resins are a step above Ortho resins, and are better suited for corrosion environments, elevated service temperatures, and have greater mechanical properties. Iso resins have between 42% and 50% styrene because the higher molecular weight more solvent is required to create a workable viscosity. Iso’s better properties do bring higher cost as compared to Ortho Resins.
Dicyclopentadiene (DCPD) resins are used for applications requiring high surface finish. This is due to their low volumetric shrink rate. Physical properties are similar to the Ortho resins, but toughness is sacrificed along with the ability to create strong secondary bonds. DCPD resins are on the low end of styrene content, ranging from 35% to 38%. DCPD resins are commonly blended with other resins to minimize the negative aspects and increase positive aspects of these resins.
Vinylesters are used in applications requiring superior corrosion resistance or toughness properties. Vinyesters are a formulation of epoxy resin and methacrylic acid, resulting in a polymer that has characteristics of polyester and epoxy.
Role of Gelcoat
Gelcoat is the decorative surface found on fiberglass parts such as boats, bathtubs, and restaurant seats. This outer layer is needed for aesthetics and protection of the underlying laminate structure. Chemically it is unsaturated polyester/vinylester resin that is unreinforced but heavily filled with a complex variety of additives. These additives are used to determine its color, UV stability, and chemical resistance.
The manufacture of fiberglass parts typically requires a gelcoat layer to aid in the release of the parts from the mold. The parts that will be painted also are manufactured with gelcoat but it is a “sandable” variety. These parts are often automotive-related, and may include pickuptruck toppers, fiberglass kitcar bodies, and other aftermarket add-ons such as running boards or hood scoops.
The unsaturated polyester/vinylester gelcoat is directly compatible with resins and laminate of the same chemistry. Gelcoat can be used with epoxy resins but requires a tiecoat for adhesion because of the chemistry difference.
Gelcoat is applied at 18 to 25 mils (thousandths) and will lose thickness as it cures. Typically when it is dry on the part, it can be down to 12 to 18 mils. This is a lot thicker than a painted surface. One of the disadvantages of gelcoat is that it can be more difficult to repair, especially with color matching. The thickness typically allows for sanding out scratches and blemishes, but going through can be painful and will require a respray. The outer layers of gelcoat will likely discolor over time due to UV degradation, and sanding and buffing into the underlying gelcoat may cause discoloration as the layers are different colors depending upon the depth.
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