Vinyl chloride, primarily used in manufacturing PVC plastic, poses significant health risks upon exposure. It's rapidly metabolized in the liver, forming metabolites that can cause liver damage, disrupt cellular functions, and lead to the formation of reactive oxygen species. This can result in oxidative stress and damage to cellular components like DNA, proteins, and lipids. Long-term exposure is notably associated with an increased risk of a rare form of liver cancer known as hepatic angiosarcoma, as well as lung and brain cancers. Acute exposure may lead to symptoms like dizziness, nausea, and headache. Its toxic effects are thus both immediate and delayed, impacting various organs, but with a notable affinity for affecting liver health. Regulatory measures limit occupational exposure, though incidents of accidental release pose significant health hazards.

Splicing yarn is a crucial technique for knitters and crocheters to join new yarn seamlessly, especially when a skein runs out. One effective method is the Russian Join. First, thread a needle with one end of your yarn. Then, insert the needle back into the yarn strand, creating a loop, and pull through, leaving a small loop. Take the end of your new yarn, thread it through the loop of the old yarn, and then, similarly, weave it back into itself. Pull both ends to tighten the loops, effectively locking the yarns together without bulky knots. This method is particularly useful for woolen yarns, as their fibers interlock for a stronger join. However, it might not be ideal for slick, synthetic yarns that could slip apart more easily.

Polypropylene (PP) is a thermoplastic polymer known for its resilience and resistance to many chemical solvents, bases, and acids. It doesn't dissolve easily in most common solvents at room temperature. However, it can dissolve or at least swell in some solvents at elevated temperatures. A notable chemical that can dissolve polypropylene is p-xylene when heated above the polymer’s melting point. The dissolution process typically requires temperatures around 90 to 100 degrees Celsius (194 to 212 degrees Fahrenheit). Other aromatic solvents like o-xylene and chlorinated hydrocarbons might also dissolve or swell polypropylene under specific conditions. Nonetheless, practical dissolution for recycling or recovery purposes is challenging due to the high temperature required and potential safety concerns. Always ensure appropriate safety measures and consult material safety data sheets (MSDS) when handling chemicals.