Modification of Poly(3-Hydroxybutyrate) with a Linear Polyurethane Modifier and Organic Nanofiller—Preparation and Structure–Property Relationship

The growing demand for products made of polymeric materials, including the commonly used polypropylene (PP), is accompanied by the problem of storing and disposing of non-biodegradable waste, increasing greenhouse gas emissions, climate change and the creation of toxic products that constitute a health hazard of all living organisms. Moreover, most of the synthetic polymers used are made from petrochemical feedstocks from non-renewable resources. The use of petrochemical raw materials also causes degradation of the natural environment. A potential solution to these problems is the use of biopolymers. Biopolymers include biodegradable or biosynthesizable polymers, i.e., obtained from renewable sources or produced synthetically but from raw materials of natural origin. One of them is the poly(3-hydroxybutyrate) (P3HB) biopolymer, whose properties are comparable to PP. Unfortunately, it is necessary to modify its properties to improve its processing and operational properties. In the work, hybrid polymer nanobiocomposites based on P3HB, with the addition of chain, uncross-linked polyurethane (PU) and layered aluminosilicate modified with organic salts (Cloisite^®30B) were produced by extrusion process. The introduction of PU and Cloisite^®30B to the polymer matrix (P3HB) influenced the processing parameters beneficially and resulted in a decrease in the extrusion temperature of more than 10 °C. The influence of the simultaneous addition of a constant amount of PU (10 m/m%) and the different amounts of nanoadditives (1, 2 and 3 m/m%) on the compatibility, morphology and static mechanical properties of the resulted nanobiocomposites were examined. The component interactions by Fourier transformation infrared spectroscopy (FTIR) analysis, nano- and microscale structure studies using small-angle X-ray scattering (SAXS) and morphology by scanning electron microscopy (SEM) were carried out, and the hardness and tensile strength of the obtained polymer nanobiocomposites were determined. FTIR analysis identified the compatibility of the polyester matrix, PU, and organomodified montmorillonite, the greatest being 3 m/m% Cloisite30B content. The addition of PU to the polyester elasticizes the material and decreases the material's strength and ductility. The presence of nanoclay enhanced the mechanical properties of nanobiocomposites. The resulting nanobiocomposites can be used in the production of short-life materials applied in gardening or agriculture.