The interest in polymer materials from renewable resources has been over the last years continuously growing in the academic world as well as in the industry, due to the increasing necessity of differentiation of energy resources. Today bio-based materials are receiving attention not only in the biomedical and agricultural fields but also in packaging applications (rigid or flexible). Poly(lactic acid) (PLA) is particularly attractive due to its optical and thermal properties, and it is considered an ideal candidate for the substitution of petrochemical based polymers (e.g. poly(styrene), poly(ethylene terephthalate)). On the other hand, the large scale application of PLA is often limited by its mechanical properties and its low gas and vapor barrier. In this context, nanocomposite materials offer a new and promising prospective since they exhibit significant changes of physical properties even in the presence of a small amount (i.e. less than 5%) of an inorganic part, compared to even tenfold amounts used in "traditional" composites. In general, the characteristics of these poly-phase systems depend on the nature of the components and also on the final morphology and chemical interactions between the phases. In this work bio-polyester based nanocomposites, with specific functional properties for flexible packaging applications, were prepared via melt blending of raw or modified PLA and lamellar inorganic nanoparticles (i.e.; phyllosilicates and layered double hydroxides or hydrotalcite-like systems). All the composites were prepared in a mechanical discontinuous mixer by varying the experimental parameters (temperature, time, blade rate) in order to assess a good dispersion of the inorganic filler at the nanometer scale. Cationic and anionic clays organically modified with phenyl groups as well as with polar groups, such as hydroxyl-groups, and functional fluorescent moieties were specifically investigated and ad-hoc prepared. In particular, it was examined how the modifier/surfactant promotes the polymer-filler interactions favoring the dispersion of the nanolamellas and the intercalation of polymer chains. In addition, functionalized bio-polyesters were prepared and used as reactive compatibilisers to improve the dispersion of the nanofiller into the PLA matrix. Functionalized PLA and poly(butilene succinate-co-adipate) PBSA samples were prepared by free radical post-reactor modification (grafting of low molecular weight sustainable chemicals bearing functionalities capable of nucleophilic reactions, like the itaconic anhydride) as well as by trans-esterification methods. The grafting efficiency was determined by FT-IR and 1H-NMR, while the molecular weight of the polymer before and after the reaction was calculated by SEC for evidencing changes of the macromolecular structure due to secondary reactions. Thermo-mechanical features (DSC, TGA) and morphological characteristics (WAXD, SEM, TEM) of all the nanocomposites were investigated. Data collected will be discussed to provide new insights about the dispersion of lamellar inorganic solids in PLA.
Inorganic nanohybrids based on bio-polyesters from renewable resources
FCicogna;
2012
Abstract
The interest in polymer materials from renewable resources has been over the last years continuously growing in the academic world as well as in the industry, due to the increasing necessity of differentiation of energy resources. Today bio-based materials are receiving attention not only in the biomedical and agricultural fields but also in packaging applications (rigid or flexible). Poly(lactic acid) (PLA) is particularly attractive due to its optical and thermal properties, and it is considered an ideal candidate for the substitution of petrochemical based polymers (e.g. poly(styrene), poly(ethylene terephthalate)). On the other hand, the large scale application of PLA is often limited by its mechanical properties and its low gas and vapor barrier. In this context, nanocomposite materials offer a new and promising prospective since they exhibit significant changes of physical properties even in the presence of a small amount (i.e. less than 5%) of an inorganic part, compared to even tenfold amounts used in "traditional" composites. In general, the characteristics of these poly-phase systems depend on the nature of the components and also on the final morphology and chemical interactions between the phases. In this work bio-polyester based nanocomposites, with specific functional properties for flexible packaging applications, were prepared via melt blending of raw or modified PLA and lamellar inorganic nanoparticles (i.e.; phyllosilicates and layered double hydroxides or hydrotalcite-like systems). All the composites were prepared in a mechanical discontinuous mixer by varying the experimental parameters (temperature, time, blade rate) in order to assess a good dispersion of the inorganic filler at the nanometer scale. Cationic and anionic clays organically modified with phenyl groups as well as with polar groups, such as hydroxyl-groups, and functional fluorescent moieties were specifically investigated and ad-hoc prepared. In particular, it was examined how the modifier/surfactant promotes the polymer-filler interactions favoring the dispersion of the nanolamellas and the intercalation of polymer chains. In addition, functionalized bio-polyesters were prepared and used as reactive compatibilisers to improve the dispersion of the nanofiller into the PLA matrix. Functionalized PLA and poly(butilene succinate-co-adipate) PBSA samples were prepared by free radical post-reactor modification (grafting of low molecular weight sustainable chemicals bearing functionalities capable of nucleophilic reactions, like the itaconic anhydride) as well as by trans-esterification methods. The grafting efficiency was determined by FT-IR and 1H-NMR, while the molecular weight of the polymer before and after the reaction was calculated by SEC for evidencing changes of the macromolecular structure due to secondary reactions. Thermo-mechanical features (DSC, TGA) and morphological characteristics (WAXD, SEM, TEM) of all the nanocomposites were investigated. Data collected will be discussed to provide new insights about the dispersion of lamellar inorganic solids in PLA.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
