By: Maci Nichols, Dani Lowry, Omar Rosales and Michael Orr
Physical properties of Paint Chips
- When paint is liquid when first opened but hardens when dry.
- Paint is a thick colored liquid with a distinct smell.
- Pigments are granular solids incorporated in the paint to contribute color. Fillers are granular solids incorporate to impart toughness, texture, give the paint special properties, or to reduce the cost of the paint. Alternatively, some paints contain dyes instead of or in combination with pigments.
- Types of paint- car paint, interior paint, exterior paint, primer, base coat, clear coat
- Primer- makes it easier for the base coat to be applied.
- The clear coat must be durable enough to resist abrasion and chemically stable enough to withstand UV light. It protects the Base Coat.
- The solid paints has no effects except the color. This is the easiest type of paint to manage, and the most common type of paint for heavy transportation vehicles, construction equipment and air planes.
- The metallic paints contains aluminium flakes to create a sparkling and grainy effect, or as people generally refer as a metallic look. This paint is harder to manage than the solid paints because of the extra dimensions to consider.
Chemical Properties of Paint Chips
- Paint typically includes three main ingredients: a binder, diluent or solvent, and pigment, all of which can differ within their category.
- The binder is the film-forming component of paint. It is the only component that must be present. All other components listed are included optionally, depending on the desired properties of the cured film.
- Binders include synthetic or natural resins such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene (VAE), polyurethanes, polyesters, melamine resins, epoxy, or oils.
- The main purposes of the diluent are to dissolve the polymer and adjust the viscosity of the paint. Some paints do not have diluents, whereas some use water as a diluent.
- Pigments are used to create color, and can be classified as either natural or synthetic. Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics would include engineered molecules, calcined clays, blanc fixe, precipitated calcium carbonate, and synthetic pyrogenic silicas.
Forensic Case Study
How Forensics Analyzes It
They also use solvent tests expose the paint sample to various chemicals to look for reactions such as swelling, softening, curling and color changes.
Pyrolysis gas chromatography/mass spectrometry helps distinguish paints that have the same color, but a different chemical composition. The paint sample is heated until it breaks into fragments, and then is separated into its various components.
To light a fire, arsonists need a flammable material and an accelerant (such as kerosene or gas). Arson investigators look for these items when they're investigating the crime scene. Because all that's usually left of the evidence is charred remains, the investigators will collect fire debris and take it back to the forensics lab for analysis.
Samples are sealed in airtight containers and then tested for residues of accelerant liquid that might have been used to start the fire. These are the most common tests performed by forensics labs during an arson investigation:
- Static headspace heats the sample, causing the residue to separate out and vaporize into the top, or "headspace" of the container. That residue is then injected into a gas chromatograph, where it's broken apart to analyze its chemical structure.
- Passive headspace heats the sample and the residue collects onto a carbon strip in the container. Then the residue collected is injected into a gas chomatograph/mass spectrometer for analysis.
- Dynamic headspace bubbles liquid nitrogen gas through the sample and captures the residue onto an absorbent trap. The trapped compounds are then analyzed using gas chromatography.
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