Thermomechanical Properties and Biodegradation Behavior of Itaconic Anhydride-Grafted PLA/Pecan Nutshell Biocomposites.

The use of lignocellulose-rich biowaste as reinforcing filler in biodegradable polymers represents a sustainable option to obtain cost-effective bio-based materials to be used for several applications. In addition, the scarce polymer-biofiller interaction can be improved by reactive functionalization of the matrix. However, the obtained biocomposites might show high thermal deformability and possibly a slow biodegradation rate. In this work, polylactic acid (PLA) was first chemically modified with itaconic anhydride, and then biocomposites containing 50 wt.% of pecan (Carya illinoinensis) nutshell (PNS) biowaste were prepared and characterized. Their physical and morphological properties were determined, along with their biodegradation behavior in soil. Moreover, the effects of two environmentally friendly physical treatments, namely ball-milling of the filler and thermal annealing on biocomposites, were assessed. Grafting increased PLA thermal-oxidative stability and crystallinity. The latter was further enhanced by the presence of PNS, achieving a 30% overall increase compared to the plain matrix. Accordingly, the biocomposites displayed mechanical properties comparable to those of the plain matrix. Thermal annealing dramatically increased the mechanical and thermomechanical properties of all materials, and the heat deflection temperature of the biocomposites dramatically increased up to 60 °C with respect to the non-annealed samples. Finally, PNS promoted PLA biodegradation, triggering the swelling of the composites under soil burial, and accelerating the removal of the polymer amorphous phase. These results highlight the potential of combining natural fillers and environmentally benign physicochemical treatments to tailor the properties of PLA biocomposites. The high biofiller content used in this work, in conjunction with the chemical and physico-mechanical treatments applied, increased the thermal, mechanical, and thermomechanical performance of PLA biocomposites while improving their biodegradation behavior. These outcomes allow for widening the application field of PLA biocomposites in those areas requiring a stiff and lightweight material with low deformability and faster biodegradability.

Effect of thermal annealing and filler ball-milling on the properties of highly filled polylactic acid/pecan nutshell biocomposites.

Biodegradable polymer composites reinforced with agri-food lignocellulosic biowaste represent cost-effective and sustainable materials potentially able to replace traditional composites for structural, household, and packaging applications. Herein, the preparation of polylactic acid (PLA)/pecan (Carya illinoinensis) nutshell (PNS) biocomposites at high filler loading (50 wt%) is reported, alongside the effect of two environmentally friendly physical treatments, namely ball-milling of the filler and thermal annealing on biocomposites. PNS enhanced the thermal stability, the viscoelastic response, and the crystallinity of the polymer. Furthermore, filler ball-milling also increased the melt fluidity of the biocomposites, potentially improving melt processing. Finally, the presence of PNS remarkably enhanced the effect of thermal annealing in the compounds. In particular, heat deflection temperature of the biocomposites dramatically increased, up to 60 °C with respect to the non-annealed samples. Overall, these results emphasize the potential of combining natural fillers and environmentally benign physical treatments to tailor the properties of PLA biocomposites, especially for those applications which require a stiff and lightweight material with low deformability.

Lignin and holocellulose from pecan nutshell as reinforcing fillers in poly (lactic acid) biocomposites.

Lignocellulose from agro-food biowaste represents a valuable source of cost-effective structural fillers for wholly renewable polymer composites. In this work, pecan (Carya illinoinensis) nutshell (NS) fiber and its structural components, holocellulose (HC) and acid insoluble lignin (AIL), were isolated, characterized and used as reinforcing fillers to manufacture poly(lactic acid) (PLA) based biocomposites. Thermal, morphological and mechanical properties of the prepared materials were analyzed. NS and HC acted as heterogeneous nucleating agents, potentially able to control PLA physical aging. Moreover, they significantly enhanced the viscoelastic response of PLA, mainly restricting the melt molecular mobility due to hydrodynamic effects and the formation of a three-dimensional particulate network. Flexural tests demonstrated that HC induced a 25% increase in modulus compared to the plain polymer. AIL, conversely, conferred higher ductility to the PLA matrix producing an increase in stress and strain at break of 55% and 65%, respectively. Finally, all the biocomposites showed lower resilience with respect to plain PLA due to the lack of chemical adhesion between filler and matrix. These results emphasize the potential of NS as a source of reinforcing filler in polymer-based biocomposites.

From biowaste to bioresource: Effect of a lignocellulosic filler on the properties of poly(3-hydroxybutyrate).

A lignin-rich residue (LRR) obtained as a by-product from the fermentative bioethanol production process, and commercial alkali lignin (AL), were used as fillers for the preparation of bio-based blends and composites with poly(3-hydrobutyrate) (PHB). Chemical characterization of LRR demonstrated that the filler contained sugar residues. Rheological and thermal characterization of the blends demonstrated that LRR did not affect thermal stability of PHB, while AL had a strong pro-degrading effect. Addition of suitable amounts of LRR dramatically affected the rheological behavior of the polymer melt, suggesting that the additive can modify polymer processability. LRR was also a heterogeneous nucleating agent, potentially able to control the physical aging of PHB. Lower resilience and elongation at break values were found for the biocomposites, due to the poor interfacial adhesion between filler and matrix. Biodegradation behavior of the composites was qualitatively assessed by analyzing the surface of soil buried films. Significant surface degradation was observed for PHB, while the process was retarded at high filler concentration, as LRR inhibited hydrolytic and biotic polymer degradation. The reported results demonstrated the feasibility of the conversion of an agro-industrial by-product into a bio-resource in an environmentally friendly and cost-effective way.

Combining gravimetric and vibrational spectroscopy measurements to quantify first- and second-shell hydration layers in polyimides with different molecular architectures.

In-situ Fourier transform infrared (FTIR) measurements have been carried out at different relative pressures of water vapor to study the H(2)O diffusion in three polyimides differing in their molecular structure and fluorine substitution. Spectral data have been analyzed by difference spectroscopy, least-squares curve fitting, and two-dimensional (2D) correlation spectroscopy, which provided molecular level information on the diffusion mechanism. In particular, two distinct water species were identified corresponding, respectively, to the first and second-shell hydration layers. The spectroscopic analysis demonstrated that the relative population of these species is a function of the total water content in the system. A method has been devised to quantify the water concentration in the two hydration layers, based on a combination of spectroscopic and gravimetric data. The results have been compared with those from an earlier spectroscopic approach reported in the literature and based on the analysis of the carbonyl region.