Distinguishing between HDPE (High-Density Polyethylene) and Polypropylene can be challenging as both are popular plastics used in varied applications due to their resistance to chemicals and impact. However, there are some key differences. HDPE, recognized for its higher density, is sturdier and commonly used in products like detergent bottles and milk jugs. Polypropylene, on the other hand, has lower density, is somewhat softer, and is often utilized in automotive parts, containers, and packaging due to its higher melting point and flexibility. One simple method for identification is the float test in water: HDPE typically floats due to its lower density, while Polypropylene may also float but possesses different tactile and visual characteristics, such as being generally more rigid and having a higher resistance to heat. Additionally, most plastic items have a resin identification code stamped on them; HDPE is marked with a "2," whereas Polypropylene is identified by a "5."

Polyvinyl Chloride (PVC) is a popular plastic used in various products, from construction materials to toys. In its final form, PVC is not typically poisonous, meaning it doesn't leach chemicals under normal conditions. However, the production and disposal processes of PVC can be harmful to the environment and human health. When burned, it releases dioxins, which are highly toxic compounds. Additionally, the additives used to make PVC more flexible, such as phthalates, can leach out under certain conditions and have been linked to health issues. It's important to handle PVC products responsibly and recycle when possible to mitigate these risks.

Polyvinyl Chloride (PVC) glue, also known as PVC cement, is designed to create a strong bond by chemically fusing PVC pipes and fittings. Once cured, it's resistant to water and most chemicals, making it challenging to dissolve. However, solvents such as acetone, MEK (methyl ethyl ketone), or specific commercial products designed to break down adhesives can partially dissolve or soften PVC glue, facilitating its removal. It's important to apply these solvents in a well-ventilated area and follow safety precautions due to their potent and hazardous nature. Mechanical removal (sanding, cutting) might be necessary for complete removal.