Agro-industrial animal wastes are materials with high volume that are considered as pollutants in some cases because they do not have a useful application. In recent years, the use of natural or animal waste materials for reinforcing or filling polymers has grown. These materials have interesting properties that improve the polymer matrix performance and provide some biodegradability. The interest is based on the improvement of mechanical, thermal, isolation and biocompatibility properties, which can be improved for applications in areas such as construction, coatings, automobile and aerospace engineering.

Among the most common reinforcers or fillers of natural or animal origin used in polymers are cellulose, chitosan, keratin, and bones. The size and shape of reinforcers or fillers play an important role in bringing new features to the polymer matrix - nanoparticles in particular have drawn attention due to excellent results. The main problem faced by researchers who work with composites reinforced with natural or animal waste materials is improving the compatibility.

The aim of this Special Issue is to report original research and review articles focused on the preparation and characterization of composite materials, filled or reinforced using natural or animal wastes materials over a polymer matrix that can be synthetic or natural.

Potential topics include but are not limited to the following:

• Use of agro-industrial wastes for reinforcing polymer composites
• Preparation and characterization of polymer composites using natural or animal waste materials
• Natural fiber polymer composites
• Animal particle composites
• Environmental degradability bio-based polymer composites
• New approaches for waste management