The coefficient of static friction between two materials, such as polyurethane and polypropylene, depends on several factors, including the surface finishes, temperature, and whether any lubricants or contaminants are present. Generally, polyurethane exhibits a higher coefficient of static friction due to its elastomeric properties, providing better grip against various materials, including polypropylene. However, specific values can vary widely. For instance, a typical range for polyurethane could be around 0.4 to 1.0 against many materials, but without specific testing under controlled conditions, pinpointing an exact number for polyurethane against polypropylene is challenging. It's always recommended to conduct material compatibility tests under the intended conditions of use to ensure reliable performance.

Polypropylene fibre reinforced concrete (PFRC) is known for its increased resistance to cracking and improved ductility. However, it has its drawbacks. One significant negative is its lower modulus of elasticity compared to traditional concrete, leading to potentially less stiff structures that may not be suitable for all applications. Additionally, the fibers can decrease the workability of the concrete mix, making it harder to place and finish. This can lead to an increased reliance on admixtures to improve workability, potentially raising costs. Another issue is the uniform distribution of fibers; if not adequately mixed, it can lead to weak spots within the concrete. Furthermore, the long-term durability of PFRC in various environmental conditions, such as exposure to UV light or chemicals, remains an area of ongoing research.

CPVC glue, also known as solvent cement, can indeed be used to bond PVC pipes, but with considerations. CPVC solvent cement is formulated for higher temperature resistance compared to PVC glue, making it suitable for both CPVC and PVC applications. However, it's essential to ensure that the product is labeled for use with PVC to avoid any issues with the bond strength and durability over time. For optimal results, using the specific glue designed for the material of your piping (PVC glue for PVC pipes, CPVC glue for CPVC pipes) is recommended to ensure the integrity of the plumbing system and adhere to local plumbing codes.