Giuliana Gorrasi

Vapor barrier properties of polycaprolactone montmorillonite nanocomposites: effect of clay dispersion

Different compositions of poly(e-caprolactone) (PCL) and (organo-modified) montmorillonite were prepared by melt blending or catalyzed ring opening polymerization of e-caprolactone. Microphase composites were obtained by direct melt blending of PCL and sodium montmorillonite (MMT-Na+). Exfoliated nanocomposites were obtained by in situ ring opening polymerization of e-caprolactone with an organo-modified montmorillonite (MMT-(OH)2) by using dibutyltin dimethoxide as an initiator/catalyst. Intercalated nanocomposites were formed either by melt blending with organo-modified montmorillonite or in situ polymerization within sodium montmorillonite. The barrier properties were studied for water vapor and dichloromethane as an organic solvent. The sorption (S) and the zero concentration diffusion coefficient (D0) were evaluated for both vapors. The water sorption increases with increasing the MMT content, particularly for the microcomposites containing the unmodified MMT-Na+. The thermodynamic diffusion parameters, D0, were compared to the value of the parent PCL: both microcomposites and intercalated nanocomposites show diffusion parameters very near to PCL. At variance exfoliated nanocomposites show much lower values, even for small montmorillonite content. In the case of the organic vapor, the value of sorption at low relative pressure is mainly dominated by the amorphous fraction present in the samples, not showing any preferential adsorption on the inorganic component. At high relative pressure the isotherms showed an exponential increase of sorption, due to plasticization of the polyester matrix. The D0 parameters were also compared to those of the unfilled PCL; in this case, both the exfoliated and the intercalated samples showed lower values, due to a more tortuous path for the penetrant molecules.

Transport properties of organic vapors in nanocomposites of organophilic layered silicate and syndiotactic polypropylene

Syndiotactic polypropylene (sPP) nanocomposites were obtained by melt blending synthetic fluorohectorite modified octadecyl ammmonium ions (OLS), and maleic-anhydride-grafted isotactic polypropylene (iPP-g-MA) as compatibilizer. The composition of the inorganic material was varied between 5 and 20 w/w%. Films of the composites were obtained by hot press molding the pellets. Melt-direct polymer intercalation of sPP into the OLS gave rise to nanocomposites in which the silicate layers were delaminated at low clay contents, and ordered to intercalated structures at the highest clay content. The elastic modulus was higher than for the pure polymer in a wide temperature range and increased with the inorganic content. The transport properties were measured for dichloromethane and n-pentane. The sorption was reduced compared to pure sPP. There were not significative differences between the samples having different inorganic contents. The diffusion coefficient decreased with increasing clay content. Permeability (P) showed a strong decreasing dependence on the clay content. The improvement of the barrier properties was largely caused by the reduced diffusion.

Dispersion of halloysite loaded with natural antimicrobials into pectins: Characterization and controlled release analysis

This paper reports the preparation and characterization of green composites based on pectins and nano-hybrids composed of halloysite nanotubes (HNTs) loaded with rosemary essential oil. Different hybrid percentages were mixed into a pectin matrix, by ball milling in the presence of water. Cast films were obtained and analyzed. Structural organization and physical properties (thermal, mechanical, barrier to water vapor) were correlated to the nano-hybrid content. A preliminary study on the kinetics of release of the rosmarinic acid, chosen as a model molecule, was also performed. This work showed the potential of these systems in the active packaging field where controlled release of active species is required.

Effect of Filler Content and Size on Transport Properties of Water Vapor in PLA/Calcium Sulfate Composites

Starting from calcium sulfate (gypsum) as fermentation byproduct of lactic acid production process, high-performance composites have been produced by melt-blending polylactide (PLA) and beta-anhydrite II (AII) filler, i.e., calcium sulfate hemihydrate previously dried at 500 degrees C. Characterized by attractive properties due to good filler dispersion throughout the polyester matrix and favorable interactions between components, these composites are interesting for potential use as biodegradable rigid packaging. The effect of filler content and mean particle diameter on the barrier properties such as sorption and diffusion to water vapor has been examined and compared to unfilled PLA. Even without additional treatments, the presence of the filler introduced constraints on molecular mobility in the permeable phase of amorphous PLA and the amount of solvent absorbed appears lower in the highly filled composites. Surprisingly, for PLA-30% AII compositions, by addition of filler characterized by high mean particle diameter (e.g., 43 microm) the thermodynamic diffusion parameter, D(0), decreased up to 2 orders of magnitude. The dimension of filler particles and their percentage in the continuous polymeric phase seem to be the most important parameters that determine the barrier properties of the PLA-AII composites to water vapor.

Pectins filled with LDH-antimicrobial molecules: Preparation, characterization and physical properties

Nanohybrids of layered double hydroxide (LDH) with intercalated active molecules: benzoate, 2,4-dichlorobenzoate, para-hydroxybenzoate and ortho-hydroxybenzoate, were incorporated into pectins from apples through high energy ball milling in the presence of water. Cast films were obtained and analysed. X-ray diffraction analysis showed a complete destructuration of all nanohybrids in the pectin matrix. Thermogravimetric analysis showed a better thermal resistance of pectin in the presence of fillers, especially para-hydroxybenzoate and ortho-hydroxybenzoate. Mechanical properties showed an improvement of elastic modulus in particular for LDH-para-hydroxybenzoate nanohybrid, due probably to a better interaction between pectin matrix and nanohybrid layers. Barrier properties (sorption and diffusion) to water vapour showed improvement in the dependence on the intercalated active molecule, the best improvement was achieved for composites containing para-hydroxybenzoate molecules, suggesting that the interaction between the filler phase and the polymer plays an important role in sorption and diffusion phenomena. Incorporation of these active molecules gave antimicrobial properties to the composite films giving opportunities in the field of active packaging.

Mechanical milling as a technology to produce structural and functional bio-nanocomposites

“Solid state mixing”, such as mechanical milling (MM), represents an ecological and economical alternative to achieve homogeneous dispersion of nano-fillers into biodegradable polymers. The advantage of working at low temperatures, without a solvent and with almost any type of polymer matrix, opens new and unexplored routes for the preparation of advanced functional materials. The use of mechanical milling contains within itself several advantages, including a strong reduction of environmental disposal, the control of the degradation processes associated with high temperature, the compatibilization of immiscible blends and the treatment of waste disposal and recycled materials. The simultaneous formation and dispersion of nanoparticles, the promotion of mechano-chemical reactions and the proper manipulation of thermo-sensitive active molecules such as antimicrobials, oxygen scavengers and antibiotics are other advantages of this process. The aim of the current work is to review the recent literature on the use of MM as a green technique to produce bio-nanocomposites. It is demonstrated how this technology could be considered an interesting option for the fabrication of novel nanostructured materials from environmental friendly resources.

Influence of the crystallinity on the transport properties of isotactic polypropylene

Samples of polypropylene of varying crystallinity were obtained by blending isotactic with atactic polypropylene, and the crystallinity determined by X-ray diffraction and differential scanning calorimetry. Crystallinity ranged between 20 and 75%. The transport properties of dichloromethane were analysed varying the activity of the vapour. We observed that the sorption decreases, as the crystallinity increases, proportionally to the decrease of the amorphous fraction. As matter of the fact, the specific sorption, normalized by the amorphous fraction, does not depend on the crystallinity. At variance, a simple correlation between the thermodynamic diffusion coefficient and the crystallinity was not obtained; at low values of this parameter, up to 40%, the zero concentration diffusion coefficient is independent of it. A sharp transition separates a range of crystallinities, in which the diffusion parameter decreases, increasing the crystallinity, due to the tortuosity of the path, and shows that the presence of the impermeable crystals is important only for values higher than 50%.

Carbon nanotube induced structural and physical property transitions of syndiotactic polypropylene

In this paper we have studied the effect of increasing carbon multi-walled nanotube (CNT) concentration in composites of syndiotactic polypropylene (sPP) having the same crystalline form but different morphologies. The attention was focused on the form I of sPP with different degrees of perfection (in terms of percentages of chains in helical conformation, crystal dimensions and crystallinity) obtained using two different quenching temperatures from the melt, i.e. 25 and 100 °C. We observed a decreasing effect of the crystallization temperature on increasing the nanotube content up to the samples with 10% of CNT, that show a very similar structural organization independent of the undercooling. Only the amorphous phase turns out more relaxed in the samples crystallized at the highest temperature. Either the thermal or the mechanical properties are improved on increasing the CNT content in both series of samples. The electrical conductivity increases in a similar manner in both series of samples and between 1 and 3 wt% it shows a sizable step of about eight orders of magnitude, a phenomenon that can be regarded as the onset of a percolating structure for which charge transport may take place.

Transport Properties of Water Vapor in Polylactide/Montmorillonite Nanocomposites

Abstract Both intercalated and exfoliated poly(L‐lactide) (PLA) layered aluminosilicate nanocomposites were synthesized and characterized in terms of barrier properties. Intercalated polylactide/montmorillonite nanocomposites were obtained by melt blending PLA and a montmorillonite modified with bis‐(2‐hydroxyethyl)methyl (tallowalkyl) ammonium cations (MMT) (1, 3, 5, and 10 wt/wt%). A sample containing 3 wt% of MMT was prepared with 20 wt% of PEG1000 as plasticizer. Exfoliated nanocomposite containing 3 wt% of MMT was synthesized by in situ coordination‐insertion ring‐opening polymerization of L,L‐lactide, after adequate activation of the primary hydroxyl groups functionalizing the organo‐modifier. The barrier properties were studied for water vapor at 30°C. The sorption (S) and the zero‐concentration diffusion coefficient (D 0) were evaluated. The sorption curves of water vapor in all the samples follow the dual‐sorption behavior. The amount of solvent absorbed derived from the linear part of the curve appears lower in the intercalated nanocomposites for all studied MMT content than for the exfoliated sample. The thermodynamic diffusion parameters, D 0, decreased by one order of magnitude with increasing MMT content from 0 to 10 wt% in the intercalated samples. In comparison with the value of D 0 for the parent unfilled PLA, the intercalated samples containing 3 wt% of MMT (with or without PEG 1000) were found to be slightly lower. On the other hand, the exfoliated nanocomposite showed strong deviation in the D 0 value, being lower by about two orders of magnitude with respect to the results obtained for all the other samples (unfilled and intercalated). The exfoliation of the inorganic component in the continuous polymeric phase seems to be the most important factor to improve the barrier properties of the material to water vapor.

Transport properties of the mesomorphic form of poly(ethylene terephthalate)

The mesomorphic form of poly(ethylene terephthalate), present in samples drawn at 60°C at a draw ratio of 4, was studied by analysing the transport properties of dichloromethane vapours. The reduced sorption with respect to the amorphous sample indicates that the mesophase is impermeable to the vapours at low activity, and this allows the determination of the fraction of mesophase in the drawn samples.