1,721,316 research outputs found
Poly(butylene succinate) and poly(butylene succinate-co-adipate) for food packaging applications: Gas barrier properties after stressed treatments
No full textAliphatic polyester resins present the versatility of common plastics and are characterized by a good stability under ordinary conditions. They have acquired significant interest as environmentally friendly thermoplastics for a wide range of application, like food packaging field. We have investigated the permeability behavior of commercial poly(butylene succinate) (PBS) and poly(butylene succinate-co-adipate) (PBSA) polymers after food contact simulants and photo and thermal-oxidative degradation processes. Each stressed treatment was applied on thin film. Barrier properties to different gases (oxygen and carbon dioxide) were evaluated, showing that the chemical composition of the polymer strongly influenced the permeability to the gasses. Further, the same samples were tested at different temperatures, from 5 °C to 40 °C, in order to understand the effect of the temperature on the permeability behavior, and to calculate the process activation energy. Relations that bind the diffusion coefficients (D) and solubility (S) with temperature were studied. Differential Scanning Calorimetry (DSC) and FT-IR analyses were carried out in order to establish a correlation between permeability and sample structure/crystallinity. Negligible changes were evidenced in the polymers by means of DSC and FTIR measurements indicating structural stability of the polymers under process conditions. Gas barrier behavior, instead, resulted mainly affected by the process conditions, because mainly dependent on several chemical-physical factors. In both cases, no severe damage of the materials was observed
Polyvinyl chloride biodegradation by Pseudomonas citronellolis and Bacillus flexus
Full text linkThe accumulation of high amounts of petroleum-derived plastics in the environment has raised ecological and health concerns. The aim of this work was to study the biodegradative abilities of five bacterial strains, namely Pseudomonas chlororaphis, Pseudomonas citronellolis, Bacillus subtilis, Bacillus flexus and Chelatococcus daeguensis, towards polyethylene, polypropylene, polystyrene and polyvinyl chloride films under aerobic conditions. Preliminary screening resulted in the selection of P. citronellolis and B. flexus as potential PVC film degraders. Both strains were able to form a biofilm on the plastic film surface and to cause some modifications to the FTIR spectra of biomass-free PVC films. The two strains were then used to set up a PVC film biodegradation assay in 2-liter flasks. After 45 days incubation, fragmentation of the film was observed, suggesting that PVC biodegradative activity took place. Gel permeation chromatography analysis showed a reduction in average molecular weight of 10% for PVC incubated with P. citronellolis, with PVC polymer chains apparently attacked. Based on these results, the P. citronellolis strain was selected for biodegradation assays of two waste PVC films, used either nonsterile or subjected to ethanol sterilization. Chemical analyses on the incubated films confirmed the biodegradation of waste PVC plastics as shown by a gravimetric weight loss of up to about 19% after 30 days incubation. In summary, this work reports the biodegradation of PVC films by P. citronellolis and B. flexus. Both strains were shown to act mainly against PVC additives, exhibiting a low biodegradation rate of PVC polymer
Poly(propylene terephthalate) containing 4,4-sulfonylbisphenol units:effect of chemical composition on the physical-chemical properties
No full textCopolyesters containing rigid aromatic units based on 4,4'-sulfonylbisphenol (bisphenol S) have been prepared by melt mixing poly(propylene terephthalate) (PPT) with an ethoxylated bisphenol S (sulfonyldiphenol). The insertion of the bisphenol units inside the polymer chain occurred quantitatively and no side reaction has been observed. The copolymers displayed good thermal stability. The main effect of copolymerization was a lowering in the degree of crystallinity and a decrease of the melting temperature with respect to PPT. On the contrary, an increment of T-g as the content of bisphenol S units increased due to the stiffening effect of the moieties deriving from bisphenol S. The Wood equation described well the correlation between T-g and composition
Cold-crystallization of poly(butylene 2,6-naphthalate) following Ostwald's rule of stages
No full textMelt-crystallization of poly (butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 °C follows Ostwald's rule of stages, leading first to formation of a transient smectic liquid crystalline phase (LC) which then may convert in a second step into crystals, controlled by kinetics. In the present work, the PBN melt was cooled at different rates in a fast scanning chip calorimeter to below the glass transition temperature, to obtain different structural states before analysis of the cold-crystallization behavior on heating. It was found that heating of fully amorphous PBN at 1000 K/s leads to a similar two-step crystallization process as on cooling the quiescent melt, with LC-formation occurring slightly above Tg and their transformation into crystals at their stability limit close to 200 °C. In-situ polarized-light optical microscopy provided information that the transition of the LC-phase into crystals on slow heating is not connected with a change of the micrometer-scale superstructure, as the recently found Schlieren texture remains unchanged
How Stress Treatments Influence the Performance of Biodegradable Poly(Butylene Succinate)-Based Copolymers with Thioether Linkages for Food Packaging Applications
Full text linkBiodegradable poly(butylene succinate) (PBS)-based random copolymers containing thioether linkages (P(BSxTDGSy)) of various compositions have been investigated and characterized from the gas barrier, thermal, and mechanical point of view, after food contact simulants or thermal and photoaging processes. Each stress treatment was performed on thin films and the results obtained have been compared to the same untreated film, used as a standard. Barrier properties with different gases (O2and CO2) were evaluated, showing that the polymer chemical composition strongly influenced the permeability behavior. The relationships between the diffusion coefficients (D) and solubility (S) with polymer composition were also investigated. The results highlighted a correlation between polymer chemical structure and treatment. Gas transmission rate (GTR) mainly depending on the performed treatment, as GTR increased with the increase of TDGS co-unit amount. Thermal and mechanical tests allowed for the recording of variations in the degree of crystallinity and in the tensile properties. An increase in the crystallinity degree was recorded after contact with simulant liquids and aging treatments, together with a molecular weight decrease, a slight enhancement of the elastic modulus and a decrement of the elongation at break, proportional to the TDGS co-unit content
Poly(Neopentyl Glycol Furanoate): A Member of the Furan-Based Polyester Family with Smart Barrier Performances for Sustainable Food Packaging Applications
Full text linkIn the last decade, there has been an increased interest from the food packaging industry toward the development and application of bioplastics, to contribute to the sustainable economy and to reduce the huge environmental problem afflicting the planet. In the present work, we focus on a new furan-based polyester, poly(neopentyl glycol 2,5-furanoate) (PNF) to be used for sustainable food packaging applications. The aromatic polyester was successfully synthesized with high molecular weight, through a solvent-free process, starting directly from 2,5-furandicarboxylic acid. PNF was revealed to be a material with good thermal stability, characterized by a higher Tgand Tmand a lower RAF fraction compared to poly(propylene 2,5-furanoate) (PPF), ascribable to the two methyl side groups present in PNF glycol-sub-unit. PNF's mechanical characteristics, i.e., very high elastic modulus and brittle fracture, were found to be similar to those of PPF and PEF. Barrier properties to different gases, temperatures and relative humidity were evaluated. From the results obtained, PNF was showed to be a material with very smart barrier performances, significantly superior with respect to PEF's ones. Lastly, PNF's permeability behavior did not appreciably change after contact with food simulants, whereas it got worse with increasing RH, due to the polar nature of furan ring
Barrier properties of poly(propylene cyclohexanedicarboxylate) random eco-friendly copolyesters
Full text linkRandom copolymers of poly(propylene 1,4-cyclohexanedicarboxylate) containing different amounts of neopentyl glycol sub-unit were investigated from the gas barrier point of view at the standard temperature of analysis (23 °C) with respect to the three main gases used in food packaging field: N2, O2, and CO2. The effect of temperature was also evaluated, considering two temperatures close to the Tg sample (8 and 15 °C) and two above Tg (30 and 38 °C). Barrier performances were checked after food contact simulants and in different relative humidity (RH) environments obtained with two saturated saline solutions (Standard Atmosphere, 23 °C, 85% of RH, with saturated KCl solution; Tropical Climate, 38 °C, 90% RH, with saturated KNO3 solution). The results obtained were compared to those of untreated film, which was used as a reference. The relationships between the gas transmission rate, the diffusion coefficients, the solubility, and the copolymer composition were established. The results highlighted a correlation between barrier performance and copolymer composition and the applied treatment. In particular, copolymerization did not cause a worsening of the barrier properties, whereas the different treatments differently influenced the gas barrier behavior, depending on the chemical polymer structure. After treatment, Fourier transform infrared analysis confirmed the chemical stability of these copolymers. Films were transparent, with a light yellowish color, slightly more intense after all treatments
Furan-based polyesters loaded with nisin for sustainable antimicrobial packaging
No full textThis work focuses on the realization of fully bio-based blends from two different furan-based polyesters and natural preservatives, to obtain innovative/active food packaging. As preservative, nisin, a polycyclic antibacterial peptide produced by Lactococcus lactis, was mixed in 2.5 wt% amount, with the homopolymer poly(trimethylene furanoate), PTF, and the copolymer poly(butylene/pentamethylene furanoate), P(BPeF). The mechanical properties of the blends evidenced a modulation for flexibility and toughness, in particular in P(BPeF), owing to the presence of nisin, keeping at the same time the thermal stability, which is a key feature of these polyesters, as well as their thermal transitions.The evaluation of the functional properties highlighted the preservation of excellent gas barrier characteristics of PTF and P(BPeF). Lastly, the addition of nisin allows for the implementation of antibacterial features,absent in the pristine polymers, as the blends showed antimicrobial activity, by disc diffusion assay, against Lactiplantibacillus plantarum and Listeria monocytogenes. PTF containing 2.5% nisin were tested also in ACE juice, pH 4.5, inoculated with Listeria monocytogenes at 10^2 CFU/mL and stored at 4°C. L. monocytogenes growth was checked for 12d. After 8 d, it decreased under the detection limit in the sample with active packaging. In the control sample, the pathogenic species remained constant during the juice shelf-life
Bio-based poly(propylene 2,5-furandicarboxylate/cyclohexanedicarboxylate) multiblock copolymers for food packaging applications
No full textEnthalpy of formation and disordering temperature of transient monotropic liquid crystals of poly(butylene 2,6-naphthalate)
No full textMelt-crystallization of poly(butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 °C follows Ostwald's rule of stages via intermediate formation of a smectic liquid crystalline phase (LC-phase). The transient LC-phase has been isolated by interruption of the isothermal crystallization process at 140 °C at sub-second timescale, and then its disordering was analyzed on heating at a rate of 2000 K/s, which suppresses the transition into α-crystals. The disordering temperature of the LC-mesophase is slightly lower than 200 °C, and as such 20–30 K lower than the melting temperature of α-crystals formed from the LC-phase at 140 °C. Analysis of the bulk enthalpy of formation of the LC-phase revealed that it covers only 20–25% of the total bulk enthalpy of crystallization, which is considered further proof of its smectic nature
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