The paper describes the production and the mechanical characteristics of composites made completely of renewable raw materials. Several wastes or by-products from agro-industrial production namely hemp hurd, alfalfa, and grape stem were analyzed with respect to their thermal stability, morphological, and chemical composition in an attempt to validate their use in composites. Such natural particle fillers were used in the range of 10–50 wt% in combination with poly(lactic acid) by melt blending to obtain fully bio-based composites. These fillers were responsible for a noteworthy increase in the storage modulus. Furthermore, two micromechanical models (Voigt and Halpin–Tsai) were used to mathematically fitted the experimental data, and then the unknown moduli were extrapolated and compared with other natural fillers. Finally, the flexural strength of the bio-composites and the adhesion evaluation by exploiting Pukanszky’s model were carried out. As a result, the hemp hurd in the form of chips was the best investigated filler, which showed the highest calculated modulus of 10.5 GPa (Voigt) and the best filler–matrix interaction with “B” (Pukanszky’s coefficient) of 2.10. This information can be useful when comparison and selection of a suitable filler among the natural fillers are required.

The poor thermo-mechanical and flame-retardant properties of biopolymers are currently limiting their application and potential exploitation as sustainable polymers. The use of agricultural by-products as a functional filler for biopolymers is here presented to address the production of environmentally friendly and economically sustainable biocomposites. To this aim, hemp hurd and alfalfa particles were melt-blended with a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB) co-polymer. The 30 wt% of filler achieves an improvement of 150% in stiffness. The same composites show an increase in the heat deflection temperature over 100 C. Flameretardant properties were also evaluated evidencing strong reductions in flame spread rates (−40%) and combustion kinetics (−30%). The achieved performances are compared with those reported in the literature for PHB composites pointing out how these completely renewable materials can compete with other currently studied solutions. The new presented composites show an opportunity for the production of functional and sustainable materials through the valorization of agricultural by-products. POLYM. COMPOS., 40:3429-3437, 2019.

The present work experimentally studies the thermal performance of a solar collector integrated with a thermal storage unit to form a compact solar water heater. The storage capacity is further enhanced by attaching a phase-change storage unit containing phase change material (PCM) which is paraffin wax. The two units (tanks) take the form of two shallow rectangular boxes (compartments) tilted at 45 o to the horizon and are firmly attached to ensure complete mutual heat transfer between them. Water and PCM fill the top and bottom tanks respectively. Measurements were carried out from 8 a.m. to 4 p.m. where the temperatures at various locations in the system were measured along with ambient temperature and solar radiation intensity. Results show that the temperature of both compartments increases continuously during the simulated period with the upper tank having the higher temperatures. The PCM average temperature did not reach melting range (55 o C-60 o C) which requires either decreasing the amount of PCM or using a PCM with a lower melting point. The maximum temperatures reached are 82 o C for water and 47 o C for PCM which are measured at 4 p.m. and the maximum overall system efficiency of the system was 74% at 11:30 a.m.