Vittoria

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.

Transport Properties of Modified Montmorillonite-Poly(ε-caprolactone) Nanocomposites

A series of montmorillonite-poly(e-caprolactone) nanocomposites were prepared according to a two stage procedure. In the first step Na-type silicate clay was cation exchanged with protonated 12-aminolauric acid. In the second step e-caprolactone was intercalated in the modified clay and ring-opening polymerized. The clay content was varied regulatory from 0 to 44 wt.-%, with exfoliation of the silicate layers being detected by X-ray diffraction in the nanocomposites dispersing up to at least 16 wt.-% clay. Crystallization of poly(e-caprolactone) was not prevented in the nanocomposites, although if proceeded to a lower extent/order than in a homopolymer sample. The transport properties were investigated using water or dichloromethane as vapor permeants. In each case, a dual sorption behavior was observed as a function of the vapor activity because of the occurrence of different sorption mechanisms. The permeability of the nanocomposites to either permeant decreased with increasing clay content. In particular, the permeability behavior to water was largely dominated by the diffusion parameter.

Chemical and morphologial modifications of irradiated linear low density polyethylene (LLDPE)

Films of linear low density polyethylene (LLDPE) produced with the spherilene technology were exposed to accelerated weathering through UV irradiation at 60°C for increasing times. A different series of films were only annealed at 60°C, to differentiate the thermal effects from those due to the UV irradiation. FT–IR analysis was used to investigate the change of the chemical structure. It was found that, following the initial production of hydroperoxides, the degradation is dominated by the formation of carbonyl and vinyl species. This process proceeds slowly up to 150 h of irradiation and afterwards it accelerates, completely degrading the material. The samples exposed more than 150 h are mechanically very fragile and soon fail. Structural analysis of the irradiated samples showed that there is a perfection of the elementary cell of polyethylene, principally along the a axis, and a consistent increase of crystallinity. The first effect was found also in thermally treated samples, whereas the second is more consistent in the irradiated samples. Also the dimension of the crystals increase much more for the irradiated samples than for the annealed ones. All the effects are mostly evident for samples after 150 h of irradiation, that is when the degradation is accelerated. The chain scission due to the photo-oxidation makes the amorphous chains more mobile and free for further crystallization, and this happens mainly when the degradation occurs simultaneously in many chains.

Development of epoxy mixtures for application in aeronautics and aerospace

This work describes a successful attempt toward the development of composite materials based on nanofilled epoxy resins for the realization of structural aeronautic components providing efficient lightning strike protection. The epoxy matrix is prepared by mixing a tetrafunctional epoxy precursor with a reactive diluent which allows the moisture content to be reduced and facilitates the nanofiller dispersion step. The reactive diluent also proves to be beneficial for improving the curing degree of nanofilled epoxy mixtures. It increases the mobility of reactive groups resulting in a higher cure degree than the epoxy precursor alone. This effect is particularly advantageous for nanofilled resins where higher temperature treatments are needed, compared to the unfilled resin, to reach the same cure degree. As nanofiller, different carbon nanostructured fiber-shaped fillers are embedded in the epoxy matrix with the aim of improving the electrical properties of the resin. The results highlight a strong influence of the nanofiller nature on the electrical properties especially in terms of electrical percolation threshold (EPT) and electrical conductivity beyond the EPT. Among the analyzed nanofillers, the highest electrical conductivity is obtained by using multiwalled carbon nanotubes (MWCNTs) and heat-treated carbon nanofibers (CNFs). The achieved results are analyzed by considering the nanofiller morphological parameters and characteristics with respect to the impact on their dispersion effectiveness.

The role of carbon nanofiber defects on the electrical and mechanical properties of CNF-based resins

Heat treatment of carbon nanofibers has proven to be an effective method in removing defects from carbon nanofibers, causing a strong increase in their structural perfection and thermal stability. It affects the bonding states of carbon atoms in the nanofiber structure and causes a significant transformation in the hybridization state of the bonded carbon atoms.Nanofilled resins made of heat-treated CNF show significant increases in their electrical conductivity even at low concentrations. This confirms that enhancement in the perfection of the fiber structure with consequent change in the morphological features plays a prominent role in affecting the electrical properties. Indeed heat-treated CNFs display a stiff structure and a smooth surface which tends to lower the thickness of the unavoidable insulating epoxy layer formed around the CNF which, in turn, plays a fundamental role in the electrical transport properties along the conducting clusters. This might be very beneficial in terms of electrical conductivity but might have negligible effect on the mechanical properties.

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.

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%.

Mechanical and transport properties of irradiated linear low density polyethylene (LLDPE)

Abstract Films of a new linear low density polyethylene (LLDPE) were exposed to accelerated weathering in a UV chamber at 60°C for increasing times. The changes in the mechanical properties, due to the degradation were followed by determining the elastic modulus ( E ), the stress at the yield point ( σ y ), the post yield stress drop (PYSD), the stress at the breaking point ( σ b ), the strain at the breaking point ( ϵ b ), and the toughness ( t ). They were correlated to the exposure time and to the carbonyl index, previously determined on the same samples. All the mechanical parameters were found to be very sensitive to the chemical degradation and to the morphological changes. Furthermore the curves of the mechanical parameters as a function of the exposure time allowed the determination of the point beyond which the material becomes useless. This point corresponds to 150 h of irradiation and to a carbonyl index of 0.3. The transport properties, diffusion and sorption, of a non polar molecule, n -pentane and a more polar molecule, dichloromethane were also correlated to the changes in the molecular structure.