Chloe Zhang
Lacquer spray paint is commonly used for painting plastic models. However, it is important to consider the potential effects of lacquer thinner on plastics. Some plastics may be prone to melting or warping when exposed to lacquer thinner, while others may be more resistant. The type of plastic, thickness, and presence of any coatings can all influence how it reacts to lacquer spray paint. This raises the question: which plastics are most resistant to melting or warping when exposed to lacquer thinner?
| Characteristics | Values |
|---|---|
| Lacquer thinner melting plastics | True |
| Plastic with good resistance to lacquer thinner | Polycarbonate, PVC |
| Plastic with good resistance to electroplating | Nylon, acetal, polyester, PVC |
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What You'll Learn
Lacquer thinner tends to melt plastics
One person notes that they have seen lacquer thinner melt plastic, and they are seeking advice on which plastics to buy to avoid this issue. They are specifically looking to create phonograph record music blank discs, traditionally made from metal, but they want to use plastic as it is easier to cut into disc shapes.
Another user suggests that PVC is a good compromise as it will dissolve in the solvent but is less likely to suffer from solvent stress cracks due to exposure. Polyethylene and polypropylene can also be used but tend to swell.
Other plastics that are not resistant to lacquer thinner include EPDM, rubber, neoprene, polyurethane, and silicone.
It is worth noting that some plastics, such as LDPE, can be used to store lacquer thinner without dissolving, but the thinner may slowly diffuse through the plastic over time.
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PVC is less prone to solvent stress cracks
Polyvinyl chloride (PVC) is a type of plastic that is prone to environmental stress cracking (ESC) in organic liquids, such as alcohols or other solvents. However, compared to other plastics, it is less susceptible to solvent stress cracks. This is because PVC is a semi-crystalline plastic, and semi-crystalline plastics are less prone to stress cracks than amorphous plastics. Amorphous plastics, such as ABS, acrylic, polycarbonate, and polystyrene, are more susceptible to stress cracking because they readily form bonds with other materials. On the other hand, semi-crystalline plastics like polyethylene, polypropylene, and polytetrafluoroethylene (Teflon) are more difficult to bond with, making them less likely to experience solvent stress cracks.
The phenomenon of stress cracking and crazing can occur in both amorphous and semi-crystalline materials when exposed to a wide range of organic liquids. However, it is more commonly observed in amorphous materials, where it can lead to catastrophic failure at stresses far below the material's tensile strength. In semi-crystalline polymers like PVC, the problem is less severe, and the same combination of polymer and solvent may demonstrate varying levels of susceptibility to stress cracks depending on experimental conditions.
The formation of crazes, or voided, spongy structures, plays a crucial role in the environmental stress cracking of PVC. These crazes form across the width of linear regions of plastic deformation, and their presence indicates that the intermolecular forces between adjacent polymer chains are low relative to the yield point of the material. As the craze grows, the fibrils between the faces of the crazes break down, eventually resulting in a crack.
The resistance of a polymer to environmental stress cracking can be evaluated by studying its behaviour when exposed to different chemicals and conditions. For example, the critical strain of polycarbonate was found to vary when immersed in different liquids, with the lowest value observed when immersed in methanol. Additionally, the diffusion rates of solvent molecules in the polymer can also impact its resistance to environmental stress cracking. In the case of PVC, high pH sodium hydroxide solutions were found to significantly affect its stability under environmental stress crazing conditions.
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Nylon is prone to moisture absorption
Nylon is one of the oldest and most commonly used thermoplastics. However, it is prone to moisture absorption, which can affect its performance and physical properties. The molecular structure and chemical properties of nylon are the main reasons for its moisture absorption. Nylon film, or polyamide film, is composed of polyamide molecules, which contain amide groups that are polar and hydrophilic. This means they can interact with and absorb water molecules, especially in humid environments. Environmental humidity and temperature also play a role in the moisture absorption of nylon, with high temperatures increasing the interaction between nylon and water.
The moisture absorption of nylon can lead to size changes, reduced tensile strength, and other issues. For example, in practical applications, moisture absorption can cause inaccurate overprinting, insufficient composite strength, and foaming. Additionally, the moisture absorption may affect the barrier and airtightness of the nylon, reducing product quality.
The effects of moisture absorption on nylon can be mitigated by choosing nylon products with better water resistance. However, it is important to note that nylon parts are dry coming out of the molding machine, and the moisture absorption caused by subsequent exposure to water is not permanent. Once the parts are removed from the water, they will start to release moisture, and their properties will adjust accordingly.
Nylon 6 parts, in particular, will absorb and release moisture throughout their lifespan based on the relative humidity and temperature of their environment. It is possible to "over-dry" nylon, which can lead to the degradation of the material. Therefore, it is important to follow the manufacturer's recommendations for moisture content.
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Metals are stiffer than plastics
It is a well-known fact that metal is one of the strongest and most durable materials available, with a wide range of applications across various industries. However, this notion that metals are stiffer than plastics is not always true. Recent advancements in plastic recipes and materials have led to the development of plastics that can match or even surpass the strength of metals.
For instance, scientists at MIT have created a plastic called 2DPA-1, which boasts twice the strength of steel while maintaining an airtight seal. This innovative plastic has the potential to revolutionize various industries, offering new opportunities for durable goods and custom plastic products. Additionally, hemp plastics, which have been utilized since 1941 in Ford vehicles, exhibit strength comparable to steel and are still commonly used in vehicles today due to their full biodegradability.
The strength of plastics is a critical factor in product design and manufacturing. Plastic fabrication is often more economical and easier to work with than other materials, making it a preferred choice for many industries. With the emergence of new plastics that rival or exceed the stiffness of metals, we can expect a shift in material preferences across various sectors.
While metals have traditionally been associated with superior stiffness, plastics like 2DPA-1 and hemp plastics challenge this notion. These advancements in plastic strength open up new possibilities for product development, cost reduction, and environmental sustainability. As a result, the statement "Metals are stiffer than plastics" may soon become outdated as plastics continue to evolve and surpass traditional expectations.
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Some chemicals cause solvent stress cracking
Environmental Stress Cracking (ESC) is a common cause of unexpected brittle failure in thermoplastic polymers. ESC occurs when a material breaks upon exposure to mechanical stress in the presence of organic liquids or wetting agents, such as soap solutions. It is important to note that this phenomenon can occur even without the presence of mechanical stress, as the internal stresses in plastic specimens can be sufficient to cause failure.
One example of ESC is when polycarbonate comes into contact with low molecular weight hydrocarbons such as acetone. A small drop of this liquid on a strip of polycarbonate can cause rapid cracking upon bending. This is because the liquid environment enters the crazes (small voids close to the surface) and penetrates between the molecular chains, leading to a swelling of the structure. This local swelling effect reduces the amount of external work necessary for fracture, making it easier for the material to break.
Another example of ESC is when a piano key made from injection-moulded styrene acrylonitrile (SAN) is exposed to a ketone solvent. In this case, the vapour from the solvent condensed on the internal surface of the piano key, leading to fracture at the junction where the key connects to the metal spring. This fracture was caused by a combination of tensile stress from the spring action and the presence of the ketone solvent.
The solubility parameter of a stress-cracking agent is a measure of the cohesive attraction between fluid molecules. If the solubility parameter of the polymer matches that of the fluid, diffusion of the agent will occur and ESC is likely to follow. For instance, when polycarbonate is subjected to methanol, thick cracks form on the surface and into the polymer due to bulk diffusion and the lack of surface resistance.
In summary, some chemicals can indeed cause solvent stress cracking in plastics. This occurs through a variety of mechanisms, including diffusion, swelling, and the interaction of liquids with microscopic surface defects. ESC is a significant concern in various industries, such as the automotive industry, where polymers are subjected to a range of fluids and chemicals.
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Frequently asked questions
Lacquer thinner tends to melt plastics.
PVC, polyester, and acetal are plastics that can be used in the same electroplating process as traditional metal-based lacquers.
Polycarbonate is not a good choice as it is highly prone to melting or warping when coated with a layer of thickened nitrocellulose lacquer mixture.
Thin sheets of plastic are very prone to warping due to even small stresses.
Nylon is not a good choice as it expands and contracts with changes in atmospheric moisture content.
