Rigour (BrE) or rigor (AmE) (see spelling differences) describes a condition of stiffness or strictness. Rigour frequently refers to a process of adhering absolutely to certain constraints, or the practice of maintaining strict consistency with certain predefined parameters.
PLA stands for polylactic acid and is a resin made from corn starch. PLA is used to make clear compostable containers and PLA lining is used in cups and containers as an impermeable liner. PLA is biodegradable, and fully compostable. It uses 65 percent less energy to produce than conventional oil-based plastics and generates 68 percent fewer greenhouse gasses and contains no toxins.
Polymer processing aids are used in polymers formulation to increase the processing efficiency and quality of polymeric compounds. PPA are based on a large diversity of chemistry, and used in different polymers (polyolefins, PA, PVC and many others polymers).