Polycaprolactone composite films infused with hyperbranched polyester/reduced graphene oxide: influence on biodegradability, gas/water transport and antimicrobial properties for sustainable packaging.

Biodegradable polymers have gained great interest as ecofriendly packaging materials. However, addition of suitable fillers to the polymer matrix enhances their barrier and mechanical properties besides gaining new features such as bactericidal activity. This work deals with investigation of mechanical, gas/water transport properties and biodegradability performance of films based on polycaprolactone (PCL) reinforced by 1wt% of reduced graphene oxide (RGO) or modified graphene (mRG). To achieve this goal, nanosheets of RGO were firstly prepared then their surfaces were modified through in situ polymerization of hyperbranched polyester (PES) to obtain mRG. Then PCL was loaded with both fillers, and the nanocomposite films were prepared by a casting technique. Studying of the thermal properties of the films showed that the addition of RGO or mRG had no influence on the crystallinity of the PCL matrix. Although the mechanical characteristics of the PCL did not change when either filler was added, there was an increase in permeability and diffusivity in the presence of the fillers regardless of their composition. Nevertheless, the nanocomposites demonstrated antimicrobial properties against S. aureus and E. coli as models for Gram-positive and Gram-negative bacteria, respectively. The biodegradability test performed on the prepared film PCL, and those containing 1% of the filler, PCL/RGO, and PCL/mRG, emphasized that the film degradation became pronounced after three months for all samples.

Effect of Amino-Functionalized Polyhedral Oligomeric Silsesquioxanes on Structure-Property Relationships of Thermostable Hybrid Cyanate Ester Resin Based Nanocomposites.

Nanocomposites of cyanate ester resin (CER) filled with three different reactive amino-functionalized polyhedral oligomeric silsesquioxane (POSS) were synthesized and characterized. The addition of a small quantity (0.1 wt.%) of amino-POSS chemically grafted to the CER network led to the increasing thermal stability of the CER matrix by 12-15 °C, depending on the type of amino-POSS. A significant increase of the glass transition temperature, Tg (DSC data), and the temperature of α relaxation, Tα (DMTA data), by 45-55 °C of the CER matrix with loading of nanofillers was evidenced. CER/POSS films exhibited a higher storage modulus than that of neat CER in the temperature range investigated. It was evidenced that CER/aminopropylisobutyl (APIB)-POSS, CER/N-phenylaminopropyl (NPAP)-POSS, and CER/aminoethyl aminopropylisobutyl (AEAPIB)-POSS nanocomposites induced a more homogenous α relaxation phenomenon with higher Tα values and an enhanced nanocomposite elastic behavior. The value of the storage modulus, E', at 25 °C increased from 2.72 GPa for the pure CER matrix to 2.99-3.24 GPa for the nanocomposites with amino-functionalized POSS nanoparticles. Furthermore, CER/amino-POSS nanocomposites possessed a higher specific surface area, gas permeability (CO2, He), and diffusion coefficients (CO2) values than those for neat CER, due to an increasing free volume of the nanocomposites studied that is very important for their gas transport properties. Permeability grew by about 2 (He) and 3.5-4 times (CO2), respectively, and the diffusion coefficient of CO2 increased approximately twice for CER/amino-POSS nanocomposites in comparison with the neat CER network. The efficiency of amino-functionalized POSS in improving the thermal and transport properties of the CER/amino-POSS nanocomposites increased in a raw of reactive POSS containing one primary (APIB-POSS) < eight secondary (NPAP-POSS) < one secondary and one primary (AEAPIB-POSS) amino groups. APIB-POSS had the least strongly pronounced effect, since it could form covalent bonds with the CER network only by a reaction of one -NH2 group, while AEAPIB-POSS displayed the most highly marked effect, since it could easily be incorporated into the CER network via a reaction of -NH2 and -NH- groups with -O-C≡N groups from CER.

Advances in Bio-Based Materials for Food Packaging Applications.

Food packaging is defined as a group of boxes, envelopes, papers, and coatings that are employed in order to increase the shelf life of foodstuffs [...].

Water Sorption and Mechanical Properties of Cellulosic Derivative Fibers.

In this study, water vapor sorption, desorption properties and tensile mechanical properties of four cellulosic fibers, cotton (C), flax (F), viscose (V) and cellulose acetate (CA), were determined. The sorption and desorption isotherms were modeled using the Park model, which allowed an accurate fitting on the whole range of water activity. This model corresponds to a multi-sorption mode dividing in three sorption modes: Langmuir sorption, Henry's law and water clustering. Park's parameters were compared for the sorption and desorption isotherms for each fiber. Regardless of the fiber, differences between sorption and desorption were obtained only for the Henry sorption. The obtained sorption properties were correlated to the accessibility and the amount of sorption sites and also to the crystallinity level of the fibers. It was found that V exhibited the highest water sorption capacity due to a higher hydroxyl groups accessibility and a low amorphous fraction, followed by F, C and CA. Results from tensile tests demonstrated that F and C fibers were more rigid, more resistant and less ductile than CA and V fibers due to a difference of microstructure of the fibers. Finally, the presence of water-sorbed molecules led to a decrease in tensile modulus due to plasticization phenomenon.

Effect of Temperature and Humidity on the Water and Dioxygen Transport Properties of Polybutylene Succinate/Graphene Nanoplatelets Nanocomposite Films.

Nanocomposite films of polybutylene succinate (PBS)/graphene nanoplatelets (GnP) with a GnP content ranging from 0 to 1.35 wt.% were prepared by melt processing. The morphology of both the neat PBS and PBS/GnP nanocomposites were investigated and revealed no significant impact of GnP on the crystalline microstructure. Moisture sorption at 10 °C, 25 °C, and 40 °C were analyzed and modeled using the Guggenheim, Andersen, and De Boer (GAB) equation and Zimm-Lundberg theory, allowing for a phenomenological analysis at the molecular scale. An understanding of the transport sorption properties was proposed by the determination of the molar heat of sorption (ΔHs), and the activation energy of the diffusion (Ed) of water in the matrix since both solubility and diffusion are thermo-activable properties. Both ΔHs and Ed showed a good correlation with the water clustering theory at high water activity. Water and dioxygen permeabilities ( and ) were determined as a function of temperature and water activity. and decreased with the addition of a small amount of GnP, regardless of the studied temperature. Moreover, the evolution of as a function of water activity was driven by the solubility process, whereas at a given water activity, was driven by the diffusion process. Activation energies of the permeability (Ep) of water and dioxygen showed a dependency on the nature of the permeant molecule. Finally, from the ΔHs, Ed, and Ep obtained values, the reduction in water permeability with the addition of a low content of GnP was attributed mainly to a tortuosity effect without diffusive interfaces rather than a significant change in the transport property mechanism.

Influence of the Graphene Filler Nature on the Morphology and Properties of Melt Blended EVOH Based Nanocomposites.

In this study, ethylene vinyl alcohol (EVOH) nanocomposites elaborated by melt blending with four different fillers were investigated. Two graphene and two graphite fillers displaying various shapes were selected. The morphology, microstructure, thermal, mechanical, and barrier properties of the nanocomposite films prepared for 2 wt% fillers were analyzed with the aim to establish structure-function properties relationships. The nanocomposites properties significantly depended on the nature of the incorporated filler. The nanocomposite film prepared with the expanded graphite filler exhibited the highest Young modulus value (E = 1430 MPa) and the best barrier properties. Indeed, barrier properties, rarely studied at high water activities, evidenced a significant improvement with a decrease of the water vapor permeability by a factor 1.8 and of the oxygen permeabilities by a factor close to 2, for a critical water activity higher than 0.95. An increase of the thermal stability was also evidenced for this nanocomposite. It was shown that for all studied nanocomposites, the properties could be related to the dispersion state of the fillers and the simultaneous increase of the crystallinity of the matrix. A specific equation was proposed to take into account these both parameters to accurately predict the nanocomposite barrier properties.

Development of Breathable Pebax®/PEG Films for Optimization of the Shelf-Life of Fresh Agri-Food Products.

In this work, thin transparent breathable films were prepared for food packaging applications. The films were obtained by the solvent casting method from both the binary blends Pebax® MH1657 copolymer/ hydroxyl-terminated polyethylene glycol (PEGOH) and Pebax® MH1657/polyethylene glycol dimethyl ether (PEGDME) as well as the ternary blend Pebax® MH1657/PEGOH/PEGDME with a 50/50 and 37.5/62.5 PEGOH/PEGDME weight ratio for additive amounts comprised between 0 and 50 wt.%. The microstructure of these materials was investigated by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) analyses. Regardless of the PEG's nature, for a PEG amount inferior to 30 wt.%, the Pebax® and PEG phases were totally miscible. For higher amounts, a phase separation was obtained. In the presence of PEG, a decrease in crystallinity was obtained. The effects of the nature and amount of PEG on the thermo-mechanical, hydration, and gas (CO2, O2) transport properties were investigated. A study of the film's stability in terms of composition over time was also performed. From this work, a wide range of films could be proposed with a stable composition over time and adjustable mechanical and gas transport properties for the prolongation of the shelf-life of highly breathable fresh products.

Improvement of Barrier Properties of Biodegradable Polybutylene Succinate/Graphene Nanoplatelets Nanocomposites Prepared by Melt Process.

Polybutylene Succinate (PBS)/Graphene nanoplatelets (GnP) nanocomposites over a range of GnP from 0 to 1.35 wt.%. were prepared by a melt process. A mixture of individual graphene nanosheets and aggregates was obtained by the addition of GnP in the PBS matrix. The presence of these fillers did not significantly modify the morphology, crystalline microstructure of the matrix or its thermal stability. However, a slight reinforcement effect of PBS was reported in the presence of GnP. The water sorption isotherm modelling with Guggenheim, Andersen and De Boer (GAB) equation and Zimm-Lundberg theory allowed a phenomenological analysis at the molecular scale. The presence of GnP did not modify the water sorption capacity of the PBS matrix. From a kinetic point of view, a decrease of the diffusion coefficient with the increasing GnP content was obtained and was attributed to a tortuosity effect. The influence of water activity was discussed over a range of 0.5 to 1 and 0 to 0.9 for water and dioxygen permeability. Improvement of the barrier properties by 38% and 35% for water and dioxygen permeability respectively were obtained.

A Protein-Based Material from a New Approach Using Whole Defatted Larvae, and Its Interaction with Moisture.

A protein-based material created from a new approach using whole defatted larvae of the Black Soldier fly is presented. The larvae turn organic waste into their own biomass with high content of protein and lipids, which can be used as animal feed or for material production. After removing the larva lipid and adding a plasticizer, the ground material was compression molded into plates/films. The lipid, rich in saturated fatty acids, can be used in applications such as lubricants. The amino acids present in the greatest amounts were the essential amino acids aspartic acid/asparagine and glutamic acid/glutamine. Infrared spectroscopy revealed that the protein material had a high amount of strongly hydrogen-bonded ß-sheets, indicative of a highly aggregated protein. To assess the moisture⁻protein material interactions, the moisture uptake was investigated. The moisture uptake followed a BET type III moisture sorption isotherm, which could be fitted to the Guggenheim, Anderson and de Boer (GAB) equation. GAB, in combination with cluster size analysis, revealed that the water clustered in the material already at a low moisture content and the cluster increased in size with increasing relative humidity. The clustering also led to a peak in moisture diffusivity at an intermediate moisture uptake.

Nanoporous Cyanate Ester Resins: Structure-Gas Transport Property Relationships.

This contribution addresses the relationships between the structure and gas transport properties of nanoporous thermostable cyanate ester resins (CERs) derived from polycyclotrimerization of 1,1'-bis(4-cyanatophenyl)ethane in the presence of 30 or 50 wt% of inert high-boiling temperature porogens (i.e., dimethyl- or dibutyl phthalates), followed by their quantitative removal. The nanopores in the films obtained were generated via a chemically induced phase separation route with further porogen extraction from the densely crosslinked CERs. To ensure a total desorption of the porogen moieties from the networks, an additional short-term thermal annealing at 250 °C was performed. The structure and morphology of such nanoporous CER-based films were investigated by FTIR and SEM techniques, respectively. Further, the gas transport properties of CER films were analyzed after the different processing steps, and relationships between the material structure and the main gas transport parameters were established.

Starch/silver nanocomposite: Effect of thermal treatment temperature on the morphology, oxygen and water transport properties.

The present work reports a strategy involving the preparation of nanostructured starch based film containing silver nanoparticles (AgNPs) using a completely green chemistry process. The nanocomposite films were prepared by solution cast process. The AgNPs were in situ generated inside the polymer film by thermal treatment at different temperatures (25, 40 and 85 °C). The influence of the presence and the amount of reducing agent (glucose) were also investigated. For all nanocomposite films, the AgNPs were spherical with a diameter less than 15 nm. Contrary to the presence of glucose, thermal treatment condition was a key factor for the AgNPs structure. Crystalline AgNPs were obtained only after thermal treatment at 85 °C. Improvements of water and oxygen barrier properties near to one decade were observed in this last case and were explained by the formation of crystalline AgNPs associated to the establishment of strong interactions between AgNPs and starch polymer matrix.

Green synthesis of colloid silver nanoparticles and resulting biodegradable starch/silver nanocomposites.

Environmentally friendly silver nanocomposite films were prepared by an ex situ method consisting firstly in the preparation of colloidal silver dispersions and secondly in the dispersion of the as-prepared nanoparticles in a potato starch/glycerol matrix, keeping a green chemistry process all along the synthesis steps. In the first step concerned with the preparation of the colloidal silver dispersions, water, glucose and soluble starch were used as solvent, reducing agent and stabilizing agent, respectively. The influences of the glucose amount and reaction time were investigated on the size and size distribution of the silver nanoparticles. Two distinct silver nanoparticle populations in size (diameter around 5 nm size for the first one and from 20 to 50 nm for the second one) were distinguished and still highlighted in the potato starch/glycerol based nanocomposite films. It was remarkable that lower nanoparticle mean sizes were evidenced by both TEM and UV-vis analyses in the nanocomposites in comparison to the respective colloidal silver dispersions. A dispersion mechanism based on the potential interactions developed between the nanoparticles and the polymer matrix and on the polymer chain lengths was proposed to explain this morphology. These nanocomposite film series can be viewed as a promising candidate for many applications in antimicrobial packaging, biomedicines and sensors.

Influence of chemical structure on hydration and gas transport mechanisms of sulfonated poly(aryl ether ketone) membranes.

This work reports the influence of the chemical structure of two sulfonated poly(aryl ether ketone)s (SPAEK) on the hydration and gas transport mechanism of thin membranes made thereupon. For this purpose, two sulfonated poly(aryl ether ketone)s having the same ionic exchange capacity (IEC) but bearing a different repartition of the sulfonic acid groups along the polymer backbone were prepared. These polymers were synthesized by direct copolymerization of two specific sulfonated precursors, bisphenol AF and 4,4'-difluorobenzophenone. The morphology of the membranes was studied by transmission electron microscopy, and the thermal properties of the ionomers were determined from differential scanning calorimetry and thermogravimetric analyses. A detailed analysis of the water sorption isotherms and kinetics was performed. The gas transport properties were also determined for He, H(2), and CO(2) in the full range of water activity. From the detailed analysis of the water sorption isotherm and of the relative contributions of the Fickian diffusion and relaxation phenomena, a water sorption mechanism was proposed in relation with the SPAEK architectures and polymers' chain mobility. This mechanism allowed explaining the different evolution of the gas transport properties observed as a function of the gas nature and hydration rate.

Convenient synthesis and properties of polypropyleneimine dendrimer-functionalized polymer nanoparticles.

A simple synthesis of polymer core-dendrimer shell nanoparticles (NPs) in the 15-20-nm-diameter range is presented. Amine-terminated polypropyleneimine (PPI) dendrimers DAB-dendri-(NH(2))(4) and DAB-dendri-(NH(2))(16) (DAB4 and DAB16) are covalently attached to the surface of primary polystyrene-based NPs bearing reactive chlorobenzyl groups produced by microemulsion polymerization in the presence of a cationic surfactant. The grafting readily proceeds under mild conditions and leads to translucent aqueous suspensions of core-shell-type NPs with a high density of peripheral amine groups that have been characterized relative to their size and chemical composition. The dendritic shell acts as a protective ionizable outer layer and provides an improvement of the colloidal stability in neutral and acidic media. The metal-binding capacity of the PPI dendrimers is retained, and spectrophotometric titrations show that the dendrimer-grafted NPs can trap a large number of Cu(2+) ions (more than 900 Cu per NP-DAB16). These properties make them potentially valuable templates for the elaboration of hybrid nanomaterials. The reactivity of the external amine groups is used to link covalently azobenzene chromophores (disperse Red 1 residues) through aza-Michael addition in aqueous suspension. This simple method gives access to colored NPs with high dye contents in the outer layer (up to 1000-1500 dye molecules per NP), which indicates that dendrimer-functionalized NPs are valuable building blocks for the construction of multifunctional nanomaterials.