Polypropylene, a thermoplastic polymer widely used in various applications, is not typically characterized as brittle. Its molecular structure affords it a good balance of properties such as toughness, flexibility, and resistance to fatigue, making it less prone to cracking compared to more brittle materials like polystyrene. Polypropylene's resistance to brittleness is enhanced at room temperature, but it can become more brittle at very low temperatures. The addition of specific additives or copolymerization can further modify its properties to increase its resistance to impact, thus reducing its brittleness under certain conditions. Therefore, while not inherently brittle, the material's brittleness can be influenced by environmental conditions and material modifications.

Regluing a PVC pipe joint that has come apart is technically possible, but not recommended for a permanent fix. The original glue breaks down the surface of the PVC pipe to weld it together. Once separated, the surfaces are damaged and won't bond as reliably. A better solution is to cut out the failed joint and replace it with a new section of pipe and fittings. This ensures a secure, leak-free connection. Always ensure to use the correct type of PVC solvent cement and follow safety guidelines when working with PVC.

When choosing a drain cleaner for PVC pipes, it's crucial to avoid chemical solutions that can damage or weaken the pipe material. Enzymatic drain cleaners are generally the safest option for PVC pipes. These types of cleaners use natural bacteria or enzymes to break down organic material causing the blockage in the drain, such as hair, grease, or food particles, without the corrosive effects of chemicals. Brands like Bio-Clean and Green Gobbler offer effective enzymatic solutions that are safe for regular use in homes with PVC piping systems. It's important to follow the manufacturer's directions for use and give the product sufficient time to work, often overnight, for the best results.