Biodegradable and non-retrogradable starch-glycerol based films were obtained using citric acid (CA) as crosslinking agent at 75°C. This material allowed decreasing water vapor permeability (WVP) more than 35%, remained amorphous for at least 45 days as a result of the network formed by the CA that avoided starch retrogradation and maintained the degradability in compost, occurring only six days after the films without citric acid. A simulation of the gelatinization process of starch-glycerol with and without CA, using a differential thermal analysis device, showed that the system with CA completed the gelatinization 5°C before than the other and, CA first reacted with glycerol and then starch-glycerol-CA reaction occurred. The temperature at which the gelatinization process was carried out was critical to obtain the best results. An increase of gelatinization process temperature at 85°C in system with CA, led to a worsening on WVP and its integrity after a swelling process with dimethylsulphoxide (DMSO), compared to the films processed at 75°C.

Films of PBAT/TPS (poly(butylene adipate-co-terephthalate)/thermoplastic starch) (starch plasticized with glycerol containing citric and stearic acids) without and with 0.6 wt% starch nanoparticles were produced by extrusion. The presence of nanoparticles during the extrusion process led to a higher degree of starch gelatinization improving starch compatibility with PBAT. Nanoparticles modified the interaction between the different components of the PBAT/TPS composite. The hydroxyl groups of the starch nanoparticles interacted with starch amylose by means of hydrogen bonds. In addition, nanoparticles modified the structure of the PBAT rigid segment (BT): a shift of T m of BT toward lower temperatures and a slight shift of the relaxation of the BT segment to higher temperatures were observed. The incorporation of nanoparticles also had a reinforcing effect on the PBAT/TPS matrix. The composite presented slight increases of Young's modulus (E) and stress at break ( b ) without affecting the strain at break ( b ). The rate of biodegradability was improved with the use of starch nanoparticles. The composite showed faster deterioration than the matrix, showing the first changes in its tonality and breakdowns at only 6 days of burial in compost.

Films based on polylactic acid (PLA) reinforced with multi‐walled carbon nanotubes (MWCNT) were developed after using an excellent methodology to ensure an optimum dispersion of the filler in the matrix. The functionalization of MWCNT was carried out through a Fenton reaction to generate hydroxyl (OH) and carboxyl (COOH) groups on their walls. After that, COOH groups were lengthened by reacting with thionyl chloride and then with triethylene glycol to achieve a terminal OH distanced from the wall of the MWCNT. Nanocomposites based on PLA containing different concentrations of functionalized filler (fMWCNT: 0.026, 0.10, and 0.18 wt%) were prepared by casting. The influence of filler concentration was investigated using some techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), water vapor permeability (WVP) and uniaxial tensile mechanical properties. Excellent dispersion of fMWCNT was observed suggesting that the technique of functionalization used was appropriate. All nanocomposites presented great stability, allowing them to be processed to temperatures reaching 300°C. Furthermore, an increasing trend of ultimate tensile strength (σu) up to 20% and a decrease of WVP around 40% with the addition of only 0.10 wt% of fMWCNT were obtained. Considering these results, the new biodegradable nanocomposites developed in this work could be very promising to replace synthetic plastics that currently are used in different areas such as nanotechnology, packaging and biomedicine. POLYM. COMPOS., 37:3066–3072, 2016. © 2015 Society of Plastics Engineers

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