Polylactic acid (PLA) films were coated by coaxial electrospinning with essential and vegetable oils (clove and argan oils) and encapsulated into chitosan, in order to combine the biodegradability and mechanical properties of PLA substrates with the antimicrobial and antioxidant properties of the chitosan–oil nanocoatings. It has been established that the morphology of the electrospun nanocoatings mainly depend on the average molecular weight (MW) of chitosan. Oil beads, encapsulated into the main chitosan nanofibers, were obtained using high-MW chitosan (Chit-H). Oil encapsulated in chitosan naoparticles resulted when low-MW chitosan (Chit-L) was used. The coating layer, with a thickness of 100 ± 20 nm, had greater roughness for the samples containing Chit-H compared with the samples containing Chit-L. The coated PLA films had higher antibacterial activity when the nanocoating contained clove oil rather than when argan oil was used, for both types of chitosan. Nanocoatings containing Chit-H had higher antibacterial activity compared with those containing Chit-L, for both types of oil tested, due to the larger surface area of the rougher nanoscaled morphology of the coating layer that contained Chit-L. The chitosan–clove oil combination had higher antioxidant activity compared to the simple chitosan nanocoating, which confirmed their synergistic activities. The low activity of systems containing argan oil was explained by big differences between their chemical composition and viscosity.
BACKROUND: One of the most important properties of the azobenzene chromophores is the photochemical trans-cis isomerization induced by UV or visible light. In azopolymers, the photoisomerization induces conformational changes in the polymer chains, which in turn lead to macroscopic variations in the chemical and physical properties of the surroundings and media.RESULTS: This work reports the photochromic behaviour and surface structuring capacity of azopolymers having rigid polyimide and flexible polysiloxane structures, respectively. These polymers have good thermostabilities, with the degradation process starting above 315 • C. The glass transition temperature of the azopolyimide is 228 • C, while that of the azopolysiloxane modified with thymine is 34 • C.
CONCLUSION:The experiments show that the azobenzene groups can isomerize even in the case of the rigid polyimide, but the maximum degree of conversion to the cis isomer is less than in the case of the flexible polysiloxane. This behaviour is reversed in solution, probably due to both the thymine and azo group interactions and for conformational reasons. The azopolymers show a good surface structuring capacity. The polysiloxane is more sensitive in the case of low irradiation energy and irradiation time. By increasing the irradiation time for both polymers, the modulation depth increases and has comparable values.
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