Polymer Degradation and Stability (v.108, #C)
Editorial Board (IFC).
Co-occurrence of bacteria and fungi and spatial partitioning during photographic materials biodeterioration by Maria Bučková; Andrea Puškárová; Maria Carla Sclocchi; Marina Bicchieri; Piero Colaizzi; Flavia Pinzari; Domenico Pangallo (1-11).
The microbial spoilage and correlated surface changes of a cellulose nitrate negative film, a gelatine–silver positive print, a cardboard frame and a cellulosic envelope dated back to 1938–1940 was assessed by means of molecular methods and scanning electron microscopy (SEM). Materials characterisation was obtained with Raman, Infrared and Electronic dispersion spectroscopies. DNA was extracted from bacteria and fungi, amplified through PCR oriented to bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS), and clone libraries were constructed for each investigated material. The ITS fungal cloning was able to detect a bigger spectrum of species respect to bacterial one. Correspondence between molecular results and SEM observations was used to address the cause of biodeterioration to single species, and to map the presence of different organisms in separate niches. This investigation highlighted a co-occurrence of both bacteria and fungi on most of the substrata, and a spatial partitioning according to the different photographic materials. Moreover, for the first time, the effects of a biological attack on glassine paper were documented.
Keywords: Polymers; Biodeterioration; Glassine paper; Gelatine; Cellulose; Photographic material;
A novel phosphorus-containing poly(1,4-cyclohexylenedimethylene terephthalate) copolyester: Synthesis, thermal stability, flammability and pyrolysis behavior by Jun-Bo Zhang; Xiu-Li Wang; Qiu-Xia He; Hai-Bo Zhao; Yu-Zhong Wang (12-22).
Poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) is a commercialized semicrystalline high-temperature thermoplastic polyester, but its flammability restricted its applications in some fields. A third monomer, 2-(6-oxido-6H-dibenz < c,e > <1,2> oxaphosphorin-6-yl)-1,4-hydroxyethoxy phenylene (DOPO-HQ-HE), was used to synthesize an intrinsic flame-retardant copolyester through trans-esterification and polycondensation. Its chemical structure was confirmed by 1H NMR and ICP-AES. The crystallization behavior of PCTDs was investigated by DSC and WAXD, and found that the introduction of DOPO-HQ-HE slightly reduced the crystallization ability of PCT. TGA results showed that the incorporation of phosphorus-containing monomer improved the thermal stability of copolyesters both in nitrogen and air. Flynn–Wall–Ozawa method was used to analyze the thermal degradation kinetics of copolyesters, and found that the apparent activation energy was enhanced. The microscale combustion calorimetry (MCC) showed that PCTDs had lower heat release rate and total heat release than PCT. The results of the limiting oxygen index (LOI), the UL-94 vertical and the cone calorimeter test indicated that DOPO-HQ-HE endowed PCTDs with flame-retardant properties to some extent. Besides this, the cone calorimeter results show that the introduction of DOPO-HQ-HE remarkably suppressed the smoke release of PCT. The pyrolysis behaviors of PCT and PCTDs were investigated by Py-GC-MS, and found that the decomposition of PCT chains usually happened at ester bond and followed the random chain scission mechanism. The introduction of DOPO-HQ-HE almost had no effect on the thermal degradation mechanism of PCT.
Keywords: Poly(1,4-cyclohexylenedimethylene terephthalate); 2-(6-Oxido-6H-dibenz < c,e > <1,2 > oxaphosphorin-6-yl)-1,4-hydroxyethoxy phenylene; Copolymerization; Flame retardance; Pyrolysis;
The role of lignin in polypropylene composites with semi-bleached cellulose fibers: Mechanical properties and its activity as antioxidant by Renan Gadioli; Jaqueline A. Morais; Walter R. Waldman; Marco-A. De Paoli (23-34).
Reports on the use of bleached Eucalyptus cellulose as a reinforcing agent for polypropylene and on the use of lignin, from Eucalyptus and other vegetal species, as a stabilizer for different polymers can be found in the scientific literature. This work focuses on polypropylene composites using cellulose fibers with different bleaching levels, i.e. containing controlled lignin contents. We compared the properties and stability of composites with bleached and with semi-bleached fibers. These were prepared by twin-screw extrusion and injection molding and characterized by their tensile and flexural mechanical properties, thermogravimetry, oxidation induction time, reflectance infrared spectrophotometry and scanning electron microscopy. The kinetic evaluation of the accelerated and environmental aging of the injection molded test samples was followed by mechanical properties variation and reflectance infrared spectrophotometry. An increase in the reinforcing effect of the fibers and on the stability of the composites was observed for composites containing semi-bleached Eucalyptus fibers, with different lignin contents, compared to composites with the bleached cellulose fibers. The lignin present in these semi-bleached fibers positively affected the mechanical properties of the composites and the hindered phenols in the lignin structure acted as a primary anti-oxidant, indicating their advantageous use in comparison to the bleached fibers. Scanning electron micrographs showed that the excellent bulk fiber/matrix adhesion was not affected by accelerated or environmental aging.
Keywords: Cellulose fiber composites; Semi-bleached cellulose; Lignin; Polypropylene; Mechanical properties and stabilization;
UV degradation of genomic DNA from in vitro grown plant species: A Fourier transform infrared spectroscopic assessment by Razvan Stefan; Cristina M. Muntean; Carmen Tripon; Adela Halmagyi; Sergiu Valimareanu (35-40).
In this work, Fourier transform infrared (FT-IR) spectra of seven untreated and UV irradiated genomic DNAs extracted from leaves of different in vitro grown plant species, respectively, have been analyzed in the 800–1800 cm−1 spectral range, in order to investigate their screening characteristic features and their structural response to UV treatment at 253.7 nm. As far as the untreated genomic plant DNAs are concerned, both A and B backbone vibrational modes were detected. A low amount of Z-DNA was also found in the untreated nucleic acids, especially for DNA from Rosa. Besides, in vitro grown plant species dependent UV degradation of DNA has been observed. The major UV influence on nucleic acids from leaf tissues was observed in the case of DNA isolated from Drosera, Hypericum, Leontopodium and Rosa, respectively. It seems, that in a lesser extent is affected Sequoia DNA by UV irradiation at 253.7 nm. Particularly, alterations in nucleic acid bases, base pairing and base stacking have been found. Also, changes in DNA conformation and sugar groups were detected. The DNA conformation seems to be in our cases, a mixture of conformational states. However, A-form DNA is the predominant conformation in both non-irradiated and irradiated samples.
Keywords: DNA structure; In vitro grown plants; Leaf tissue; UV radiation; FT-IR spectroscopy;
Thermally and UV initiated degradation of polypropylene in the presence of 2,5 bis(2-furylmethylene) cyclopentanone and heterogeneous distribution of hydroperoxides assessed by non-isothermal chemiluminescence in nitrogen by J. Rychlý; L. Rychlá; A. Fiedlerová; Š. Chmela; M. Hronec (41-47).
2,5 bis(2-furylmethylene) cyclopentanone (F2C) has been shown to be a good inhibitor of thermal oxidation of polypropylene (PP). F2C structure, namely of cyclopentanone moiety linking two furan rings via conjugated system of double bonds performs captodative properties towards free radicals that may be the potential reason of its thermo-oxidation stabilization effect on polypropylene. When F2C is UV irradiated it acts as a weak photo-sensitizer probably due to carbonyl group in cyclopentanone, however, the original structure of F2C is converted fast to the products losing photo-sensitizing effect but still keeping some residual antioxidant effect on thermal oxidation of polypropylene that is probably due to 335 nm UV band. The changes of non-isothermal chemiluminescence runs in nitrogen and in oxygen and development of FTIR spectra for 0.3% of F2C in polypropylene were compared with pure polypropylene and polypropylene containing 0.3 wt. % of Irganox 1010. New observation has been presented namely that non-isothermal chemiluminescence runs in nitrogen shows the peak around 145 °C attributed to the decomposition of hydroperoxides superimposed with an additional peak appearing around the temperature of melting of polypropylene crystallites. This appears to be brought about by accelerated decomposition of hydroperoxides due to their higher concentration in heterogenous zones formed in the previous oxidation and to their increased mobility when polymer melts.
Keywords: Polypropylene; 2,5 bis(2-furylmethylene) cyclopentanone; Irganox 1010; Chemiluminescence; Photoageing; Thermal ageing;
Functionalisation and pore size control of electrospun PA6 nanofibres using a microwave jet plasma by D. Pavliňák; J. Hnilica; A. Quade; J. Schäfer; M. Alberti; V. Kudrle (48-55).
Polyamide 6 (PA6) nanofibres prepared by electrospinning were plasma treated using a microwave surface-wave jet at atmospheric pressure. The exposition to the plasma induced chemical and morphological changes of the nanofibre mats. The apparent porosity observable in SEM images was found to depend on the duration of plasma treatment. The ATR-FTIR and XPS detected increase of oxidised functional groups on the surface was consistent with kinetic model developed. The plasma treatment was compared to thermal treatment, which induced the morphological but not chemical changes of the fibres.
Keywords: Polyamide 6; Electrospun nanofibre; Microwave plasma jet; SEM; ATR-FTIR; XPS;
Flame retardancy of ethylene vinyl acetate (EVA) using new aluminum-based fillers by Roland El Hage; Amandine Viretto; Rodolphe Sonnier; Laurent Ferry; Jose-Marie Lopez-Cuesta (56-67).
Flame retardancy of EVA copolymers using three new synthesized and two commercial hydrated mineral aluminum-based fillers having different aspect ratio was studied. It was shown that the peak of heat release rate (pHRR) in cone calorimeter test significantly decreased in presence of lamellar-shaped pseudoboehmites compared to that observed in presence of aluminum trihydroxyde and boehmite. On the opposite, thermogravimetric analysis (TGA) and Pyrolysis Combustion Flow Calorimeter analysis (PCFC) did not show any significant modification between the five formulations indicating that the pHRR decrease is related to barrier effect and not to endothermic effect or to improvement of thermal stability. No relationship was found between the pHRR decrease and the melt viscosity. ESEM and EDX analyses have confirmed that the efficiency of the barrier effect in presence of the two lamellar pseudoboehmites is assigned to migration phenomena of particles which led to the quick formation of a homogeneous and cohesive insulating layer.
Keywords: Ethylene vinyl acetate; Pseudoboehmite; Flame retardancy; Filler migration;
Two novel phosphorus–nitrogen-containing halogen-free flame retardants of high performance for epoxy resin by Liqiang Gu; Guoan Chen; Youwei Yao (68-75).
Two novel halogen-free flame retardants, DP-DDE and DP-DDS, were synthesized via a one-pot procedure based on the Pudovik reactions between 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and imines directly resulting from the condensation reactions of 3-methoxy-4-hydroxybenzaldehyde with two typical curing agents, 4,4′-oxydianiline (DDE) and 4,4′-diaminodiphenylsulfone (DDS), respectively. The fire-resistant properties of DP-DDE or DP-DDS modified epoxy resins (2,2-bis(4-glycidyloxyphenyl)propane) with 4,4′-methylenedianiline as hardener were been investigated by UL-94 vertical test. Their high flame-retarding performance has been found: the epoxy thermosets with a relatively low addition amount of DP-DDE or DP-DDS (on the account of phosphorus content of 0.75 wt.% or 0.73 wt.%) can reach UL-94 V-0 flammability rating. These thermosets demonstrated excellent thermal stability, high glass transition temperature (T g > 135 °C) and high char yields (>22% at 800 °C). Moreover, the thermal degradation kinetics of the flame retardants and their corresponding epoxy thermosets were studied based on Kissinger, Ozawa and FWO methods by thermogravimetric analysis.
Keywords: Epoxy resin; Flame retardancy; Thermoset; Phosphorus; Halogen-free;
Vegetable oil-based rigid polyurethanes and phosphorylated flame-retardants derived from epoxydized soybean oil by Melissa Heinen; Annelise Engel Gerbase; Cesar Liberato Petzhold (76-86).
In this work, it has been investigated the utilization of phosphorylated polyols, derived from vegetable oils, in the formulation of rigid polyurethane foams and their property as flame-retardants. Phosphorylated polyols were used in different proportions with other polyols, such as castor oil, glycerin and glycol polyesters. In order to obtain the phosphorylated polyols, soybean oil was reacted with phosphoric acid. The obtained polyols were characterized by infrared spectroscopy (IR), nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), hydroxyl index (OH), acid value (AV), and inductively coupled plasma optical emission spectrometry (ICP-OES). The foams were prepared using a NCO/OH molar ratio 1.2:1 and poured into a box using pentane as blowing agent and polymeric diphenylmethane diisocyanate (MDI). They were characterized by means of apparent density, scanning electron microscopy (SEM), flammability test and simultaneous thermal analysis coupled with Fourier transform infrared spectrometry (SDT-FTIR). The results demonstrated that phosphorylated polyols obtained from renewable sources present flame-retardancy potential as good as the commercial ones.
Keywords: Polyurethane; Flame-retardant additive; Vegetable oil; Phosphorylated polyol;
Supramolecular evolution over an initial period of biodegradation of lactide and caprolactone based medical (co)polyesters by Jone M. Ugartemendia; A. Larrañaga; H. Amestoy; J.R. Sarasua (87-96).
Phase-structural changes and enthalpic relaxation behavior of poly(d,l-lactide) (PDLLA), poly(l-lactide) (PLLA) and poly(l-lactide-co-ε-caprolactone) (PLCL) copolymers with a lactide molar content ∼70% and having different randomness character (PLCLr 1: R = 0.69; PLCLr 2: R = 0.92) were evaluated over 7 days in phosphate buffered saline (PBS) at 37 °C. Results obtained by Temperature Modulated Differential Scanning Calorimetry (TMDSC) and Dynamic Mechanical Analysis (DMA) showed an increase in the value of enthalpic relaxation (δ) and the narrowing of the tan δ peak, respectively, indicating the reduction in molecular mobility and a more uniform distribution of the entropic states as the aging time increased. The results obtained for PLCLs were clearly affected by chain microstructural magnitudes, l LA (PLCLr 1 = 4.35 and PLCLr 2 = 3.45). Both showed a crystallization process accompanied by amorphous phase separation during the early stage in PBS. DSC and DMA results also revealed faster structural changes as a result of new supramolecular arrangements as well as a higher tendency to crystallize for PLCLr 1 regarding PLCLr 2.
Keywords: Polylactide; Poly(l-lactide-co-ε-caprolactone); Physical aging; Enthalpy relaxation; Dynamic mechanical properties; TMDSC;
An intumescent flame retardant polypropylene system with simultaneously improved flame retardancy and water resistance by Cheng-Liang Deng; Shuang-Lan Du; Jing Zhao; Zhen-Qi Shen; Cong Deng; Yu-Zhong Wang (97-107).
A traditional intumescent flame retardant (IFR) has very poor water resistance due to the existence of ammonium polyphosphate (APP). How to improve the water resistance of APP or IFR without sacrificing its flame retardancy is an important issue for the wide application of IFR. In this study, the coated APP with polysiloxane shell (Si-APP) was prepared by in situ polymerization, and was used to flame retard polypropylene (PP) together with charring agent (CA). The resulting Si-APP was characterized by Fourier transform infrared spectra (FTIR), transmission electron micrographs (TEM) and thermogravimetric (TG) analysis. The water solubility of Si-APP was also investigated. The thermal stability and combustion behaviors of PP/Si-APP/CA and PP/APP/CA composites were also investigated through TG, limiting oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter (CC) test. The results showed that the coated APP with polysiloxane shell could significantly improve the flame retardancy of IFR PP systems. At a total flame retardant loading of 25 wt%, the LOI value of PP/Si-APP/CA was 34.0%, which was higher than 30.6% of PP/APP/CA, and the UL-94 rating of the former was V-0 in the case of the specimen thickness of 1.6 mm, while the later was V-2 rating. CC test results showed that the average value of heat release rate (HRR), the total heat release (THR), and the peak of smoke production rate (SPR) of PP/Si-APP/CA decreased in comparison with PP/APP/CA system, especially, THR decreased by 50.0%. Further, the char residue of the former increased significantly compared with the latter, greatly increased by 238.9%. In addition, the thermal stability and water resistance of IFR PP composites were also improved due to the modification of APP. The mechanism for the improvement of flame retardancy was also discussed based on the experimental results. All these results illustrate that the coating of APP with polysiloxane shell is an efficient method to improve the flame retardancy and water resistance of APP-containing IFR PP systems.
Keywords: Coating; Polysiloxane; Ammonium polyphosphate; Flame retardancy; Water resistance;
Thermal effects of ionic liquid dissolution on the structures and properties of regenerated wool keratin by Arun Ghosh; Stefan Clerens; Santanu Deb-Choudhury; Jolon M. Dyer (108-115).
Keratins derived from wool and feathers are a source of raw materials for biomaterial use. Such biomaterials are essentially biodegradable polyamides, and offer many favourable features such as biocompatibility in contrast with petro-derived synthetic materials. In the present study, raw wool samples were dissolved in hot ionic liquid (1-butyl-3-methylimidazolium chloride) at temperatures ranging from 120 to 180 °C, resulting in regenerated keratins after coagulation with water. The physicochemical characteristics of the regenerated keratins were evaluated with respect to their protein profile, thermal stability, mechanical performance and SEM morphology, and contrasted with those of raw wool. Cysteine content reduced significantly on increasing temperature of ionic liquid and some disordering of protein secondary structures occurred in regenerated keratins. Keratin regenerated from a solution prepared with ionic liquid at 180 °C showed improved thermal processing properties, and it revealed dense fibrous network morphology of the film's cross-sectional surface produced under compression moulding. This in-depth study on regenerated keratins demonstrates a potential new route for the conversion of keratinous materials into bio-resin for industrial applications. However, further development is required to create keratinous materials that are melt-processable like classical synthetic polymers.
Keywords: Wool; Keratin; Ionic liquid; Bioresin; Mechanical performance;
Polyamide 4 with long-chain fatty acid groups – Suppressing the biodegradability of biodegradable polymers by Naoko Yamano; Norioki Kawasaki; Maki Oshima; Atsuyoshi Nakayama (116-122).
Polyamide 4 (PA4) is a biodegradable polymer that can be produced from biomass. We found that modifying the terminal group of PA4 with a long-chain fatty acid resulted in the suppression of its biodegradation. PA4 modified with various acyl compounds from acetyl (C2) to stearoyl (C18) chlorides were prepared and used for biodegradation tests. The biodegradation of the PA4s was evaluated using PA-4-degrading bacteria (Pseudomonas sp. ND-11) and activated sludge. The PA4-degrading bacteria grew and formed a clear zone around the colonies on the media containing PA4s with C2, C3, C6, and C10 end groups. On the other hand, PA4s with C12, C14, C16, and C18 end groups were not significantly degraded. Similar results were obtained using activated sludge. These results showed that the biodegradability of PA4 could be controlled by the molecular design of the polymer end group. Blending PA4 with fatty acid-functionalized PA4 decreased its biodegradability depending on the blend ratio. From the results of the contact angle measurements on the PA4 surfaces, it was suggested that the biodegradability was correlated to the hydrophilicity of the polymers. This method of controlling the biodegradability by adding a fatty acid group could be applied to other biodegradable polymers such as poly(butylene succinate adipate)s, ε-poly(caprolactone), and poly(lactic acid).
Keywords: Biodegradable polymer; Long-chain fatty acid; Hydrophobicity; Biodegradability;
Molecular and macromolecular structure changes in polyamide 11 during thermal oxidation by Octavie Okamba-Diogo; Emmanuel Richaud; Jacques Verdu; François Fernagut; Jean Guilment; Bruno Fayolle (123-132).
The present article reports a study of thermal oxidation of unstabilized polyamide 11 films at several temperatures (90–165 °C) under atmospheric pressure and under various oxygen pressures (up to 1.6 MPa) at 110 °C. The chemical structure changes are monitored by IR spectroscopy (carbonyl groups) and UV–visible spectrophotometry (yellowing). Molar mass changes are determined by size exclusion chromatography (SEC). By investigating the influence of oxygen pressure it is clearly shown that reactions involving P° radicals other than O2 addition cannot be neglected under atmospheric pressure. Under the conditions of this study limited to relatively low oxidation levels, IR and UV measurements indicate that carbonyl groups and chromophores responsible for yellowing have the same relative yield whatever the temperature and oxygen pressure. SEC measurements highlight the significant predominance of random chain scissions over crosslinking events. Crosslinking only appears after an induction time, presumably because it involves reactions between primary oxidation products. The ratio of carbonyl groups over chain scissions is about 7.5 at low conversion and about 2.5 at high conversion, showing that α amino alkoxy radicals are mainly transformed into imides without chain scission.
Keywords: Thermal oxidation; Polyamide; Chain scission; Carbonyl build up; Oxygen pressure;
Thermal degradation of softwood lignin and hardwood lignin by TG-FTIR and Py-GC/MS by Jing Zhao; Wang Xiuwen; Jun Hu; Qian Liu; Dekui Shen; Rui Xiao (133-138).
The structural characteristics of softwood (Chinese fir) lignin and hardwood (Maple) lignin prepared by Klason method were identified by elemental analysis and Fourier transform infrared (FTIR) spectrometry, and the pyrolytic behaviors of lignin were examined by means of thermogravimetric-Fourier transform infrared spectrometry (TG-FTIR) and Pyrolylisis-gas chromatography/mass spectrometry (Py-GC/MS). It was found that maple (hardwood) lignin contained more methoxyl groups than Chinese fir (softwood) lignin due to the enrichment of syringol units, presenting the chemical formula as C4.64H4.017O2.482 against C4.939H5.255O2.219 for Chinese fir lignin. The amounts of phenolics, methanol and CH4 evolved from pyrolysis of maple lignin were all remarkably larger than that of Chinese fir lignin through TG-FTIR analysis. For both two lignins, aromatic compounds (such as benzene, toluene and xylene) were predominantly released between 650 °C and 800 °C, due to the intensive cleavage of aryl-O-R linkages and dehydroxylation reaction on benzene-ring. The distribution of produced volatiles during lignin fast pyrolysis against furnace temperature was intensively discussed, finding that the cleavage of typical inter-unit linkages under relatively low temperature produced the guaiacol-type and syringol-type compounds, whereas the elevated temperature facilitated the cracking of methoxyl group, giving rise to the notable increase of phenol-type, catechol-type compounds and aromatic hydrocarbons.
Keywords: Klason lignin; Pyrolysis; TG-FTIR; Py-GC/MS;
4th International Conference on Biodegradable and Bio-based Polymers (BIOPOL-2013) by Alfonso Jiménez; José M. Kenny (139).
Crystallization and thermal characterization of biodegradable tri-block copolymers and poly(ester-urethane)s based on PCL and PLLA by Iván Navarro-Baena; José M. Kenny; Laura Peponi (140-150).
In this paper the crystallization behavior of biodegradable linear tri-block copolymers PLLA-b-PCL-b-PLLA and their corresponding poly(ester-urethane)s was studied and related to their thermal stability. A series of tri-block copolymers was synthesized by ring opening polymerization of l-lactic acid thus using PCL block with constant molecular weight of about 8000 g/mol and varying the amount of PLLA. The poly(ester-urethane)s were synthesized by polycondensation of the tri-block copolymers with hexamehylene diisocyanate. The crystallinity nature of the polymers was investigated by wide angle X-ray diffraction (WAXD) measurements allowing the determination of the cell structure parameters. Furthermore, the kinetic of the crystallization process from the melt was studied with differential scanning calorimetry (DSC) measurements and by using the Avrami equation to describe the process in terms of crystallization growth and rate. Finally, the thermal degradation of the tri-block copolymers as well as of the poly(ester-urethane)s was investigated by dynamic thermogravimetric analysis (TGA). It was found that the differences on the molecular structure in terms of block copolymer composition, molecular weight, crystallinity and the presence of urethane bonds, affect the degradation behavior of each block.
Keywords: Poly(l-lactic acid); Poly(ε-caprolactone); Poly(ester-urethane); Isothermal crystallization; WAXD; Thermogravimetric analysis;
Whey protein layer applied on biodegradable packaging film to improve barrier properties while maintaining biodegradability by Patrizia Cinelli; Markus Schmid; Elodie Bugnicourt; Jessica Wildner; Agostino Bazzichi; Irene Anguillesi; Andrea Lazzeri (151-157).
The aim of the present study was to verify that a whey protein-based layer can improve oxygen barrier properties of commercial compostable plastic film, while not hindering the biodegradability of the compostable film as well as not affecting the quality of the compost. The whey protein-based coating was applied on a biodegradable commercial film certified to meet the requirements of EN13432. Oxygen barrier properties were significantly improved by the presence of the whey protein layer. This result is particularly important since biodegradable packaging generally lack in maintaining barrier properties and the use of not degradable materials to improve barrier to gas and water vapour compromises the composting of the final packaging. In addition to that, it was important to assess the biodegradability of the whey protein layer itself since natural polymers may became not degradable if cross-linked or blended with not degradable additives. The material based on denatured whey protein and plasticizer presented fast biodegradability even after application on the commercial film. These positive results have potential to be used in new cost effective and ecological food packaging designs.
Keywords: Whey protein isolate; Barrier; Packaging; Biodegradable; Poly lactic acid;
Influence of thymol and silver nanoparticles on the degradation of poly(lactic acid) based nanocomposites: Thermal and morphological properties by Marina Ramos; Elena Fortunati; Mercedes Peltzer; Franco Dominici; Alfonso Jiménez; María del Carmen Garrigós; José María Kenny (158-165).
Biopolymers, such as poly(lactic acid) (PLA), have been proposed as environmentally-friendly alternatives in applications such as food packaging. In this work, silver nanoparticles and thymol were used as active additives in PLA matrices, combining the antibacterial activity of silver with the antioxidant performance of thymol. The combined action of both additives influenced PLA thermal degradation in ternary systems. DSC results showed that the addition of thymol resulted in a clear decrease of the glass transition temperature (T g) of PLA, suggesting its plasticizing effect in PLA matrices. Slight modifications in mechanical properties of dog-bone bars were also observed after the addition of the active components, especially in the elastic modulus. FESEM analyses showed the good distribution of active additives through the PLA matrix, obtaining homogeneous surfaces and highlighting the presence of silver nanoparticles successfully embedded into the bulk matrix. Degradation of these PLA-based nanocomposites with thymol and silver nanoparticles in composting conditions indicated that the inherent biodegradable character of this biopolymer was improved after this modification. The obtained nanocomposites showed suitable properties to be used as biodegradable active-food packaging systems with antioxidant and antimicrobial effects.
Keywords: Poly(lactic acid); Thymol; Silver nanoparticles; Nanocomposites; Degradation;
Water absorption and hydrothermal performance of PHBV/sisal biocomposites by J.D. Badia; T. Kittikorn; E. Strömberg; L. Santonja-Blasco; A. Martínez-Felipe; A. Ribes-Greus; M. Ek; S. Karlsson (166-174).
The performance of biocomposites of poly(hydroxybutyrate-co-valerate) (PHBV) and sisal fibre subjected to hydrothermal tests at different temperatures above the glass transition of PHBV (T H = 26, 36 and 46 °C) was evaluated in this study. The influences of both the fibre content and presence of coupling agent were focused. The water absorption capability and water diffusion rate were considered for a statistical factorial analysis. Afterwards, the physico-chemical properties of water-saturated biocomposites were assessed by Fourier-Transform Infrared Analysis, Size Exclusion Chromatography, Differential Scanning Calorimetry and Scanning Electron Microscopy. It was found that the water diffusion rate increased with both temperature and percentage of fibre, whereas the amount of absorbed water was only influenced by fibre content. The use of coupling agent was only relevant at the initial stages of the hydrothermal test, giving an increase in the diffusion rate. Although the chemical structure and thermal properties of water-saturated biocomposites remained practically intact, the physical performance was considerably affected, due to the swelling of fibres, which internally blew-up the PHBV matrix, provoking cracks and fibre detachment.
Keywords: Hydrothermal degradation; Biocomposites; Poly(hydroxybutyrate-co-valerate) (PHBV); Lignocellulosic fibres; Sisal; Statistical factorial analysis (SFA);
Biodegradable polyurethanes from crystalline prepolymers by Agata Domanska; Anna Boczkowska (175-181).
Polyurethanes in the solid state are commonly used in many structural and medical applications. They are obviously obtained by the polyaddition reaction, where usually ethylene glycol is used as the chain extender. This paper deals with the fabrication of polyurethanes from crystalline prepolymers where water is used as a chain extender. Biodegradable polyurethanes were synthesized from: poly(ε-caprolactono)diol (PCL), 4,4′methylenebis(cyclohexyl) isocyanate (HMDI) and distilled water (w) as a chain extender. The prepolymer was crystallized at three different temperatures: 7, 22 and 30 °C, respectively. The materials were subjected to degradation in a solution of phosphate buffered saline (PBS) at the temperature of 37 °C, where the solution was changed every week. The results of the physical, mechanical and thermal properties, as well as sample's surface observations after the degradation are presented in the comparison to polyurethane obtained in a polyaddition reaction with ethylene glycol as a chain extender. Biodegradable polyurethanes obtained from crystalline prepolymers extended by water exhibit better mechanical properties and higher degradation rate in a solution of phosphate buffered saline (PBS) at the temperature of 37 °C than biodegradable polyurethanes obtained by the polyaddition reaction with the application of ethylene glycol as a chain extender.
Keywords: Biodegradation; Polyurethane; Crystalline prepolymer; Poly(ε-caprolactono)diol; Phosphate buffered saline PBS; Extended by water;
Encapsulation of the natural antioxidant aureusidin in biodegradable PLA nanoparticles by M. Roussaki; A. Gaitanarou; P.Ch. Diamanti; S. Vouyiouka; C. Papaspyrides; P. Kefalas; A. Detsi (182-187).
The purpose of this article was to investigate for the first time the nanoencapsulation of a naturally-occurring flavonoid, i.e. aureusidin, exhibiting a variety of properties including antioxidant. In particular, the encapsulation efficiency of aureusidin in biodegradable poly(lactic acid) PLA nanoparticles was evaluated using the emulsification-solvent evaporation technique, while some of the pertinent parameters affecting the properties of the formed nanoparticles were investigated. The obtained results were promising, suggesting that the particular polymer-technique system is a valid choice for aureusidin encapsulation and protection.
Keywords: Encapsulation; Nanoparticles; Polymers; PLA; Aurone; Aureusidin;
Synthesis, characterization and hydrolytic degradation of polyester-urethanes obtained by lipase biocatalysis by Karla A. Barrera-Rivera; Laura Peponi; Ángel Marcos-Fernández; José M. Kenny; Antonio Martínez-Richa (188-194).
The enzymatic synthesis of α–ω-telechelic polycaprolactone diols (HOPCLOH) and block copolymers was studied. Synthesis of α–ω-telechelic PCL diols was carried out by enzymatic ring opening polymerization with Yarrowia lipolytica lipase immobilized on Lewatit VP OC K2629 and Amberlyst 15, and using ethylene glycol, diethylene glycol and polyethylene glycol as initiators. Biodegradable linear polyester-urethanes were prepared from synthesized PCL diols and hexamethylenediisocyanate (HDI). Polyester-urethanes degradation was studied using thermogravimetric analysis (TGA) and hydrolysis (alkaline, acidic and neutral). It was found that content of ether linkages influences the thermal stability and hydrolytic degradation behavior of the analyzed polyurethanes. Hydrolytic degradation proceeds faster in alkaline media, in agreement with the expected susceptibility of ester COO– bonds to degradation in the polyester urethanes.
Keywords: Degradable polyurethanes; Ring-opening polymerization; Lipase biocatalysis; Yarrowia lipolytica lipase;
Biostability of polyurethanes. Study from the viewpoint of microphase separated structure by L. Rueda; B. Fernandez d'Arlas; M.A. Corcuera; A. Eceiza (195-200).
The materials design focused on biomedical applications involves the analysis under physiological simulated conditions because it is of prime importance the determination of life-time and reliability of these materials. The goal of this work were the study of the biostability of a series of segmented thermoplastic polyurethane elastomers (STPUE), containing PTHF and PCL blocks as soft segment (SS), by means of hydrolytic degradation tests for 3 years to determine the useful life-time. Physico-chemical and thermal properties were analyzed from the viewpoint of microdomain structure. The results suggested a reorganization in hard and soft segment ordered structure by means of a greater number of hydrogen bonds which contributed to phase separation and hence low-water uptake, being less susceptible to hydrolytic attack.
Keywords: Hydrolytic degradation; Segmented thermoplastic polyurethane; Microphase separated structure; Hydrogen bonding; Hard segment;
Effect of the addition of tall oil-based polyols on the thermal and mechanical properties of ureaurethane elastomers by Kamila Pietrzak; Mikelis Kirpluks; Ugis Cabulis; Joanna Ryszkowska (201-211).
As part of this work, the test results for ureaurethane elastomers (PUURs) manufactured with the use of tall oil (TO)-based polyols with a rosin acid content ranging from 2 to 20% are presented. The goal of this study was to verify the thermal and mechanical properties of bio-based PUURs. The physicomechanical properties of PUURs were tested along with the strength (static tensile test) and thermal properties: thermogravimetry (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). A structural analysis of the materials was also carried out via Fourier transform infrared (FTIR) spectroscopy. The replacement of the chain extender with tall oil-based polyols resulted in materials with different properties, different chemical constitutions and different thermal decomposition patterns. PUURs with TO polyols had a higher thermal resistance, and this resistance increased for higher isocyanate numbers (I NCO). The thermal decomposition of the tested PUURs with TO polyols increased with the increase in the rosin acid content. The mechanical properties of the PUURs show that changing the chain extender with the TO polyols causes an increase in the storage modulus.
Keywords: Ureaurethane elastomers; Tall oil; Rosin acid; Amidization; Diethanolamine;
Hydrothermal ageing of polylactide/sisal biocomposites. Studies of water absorption behaviour and Physico-Chemical performance by O. Gil-Castell; J.D. Badia; T. Kittikorn; E. Strömberg; A. Martínez-Felipe; M. Ek; S. Karlsson; A. Ribes-Greus (212-222).
An accelerated hydrothermal degrading test was designed in order to analyse the synergic effect of water and temperature on PLA/sisal biocomposites with and without coupling agent. As well, the physico-chemical properties of biocomposites were monitored along the hydrothermal test by means of Scanning Electron Microscopy, Size Exclusion Chromatography and Differential Scanning Calorimetry. The addition of fibre induced higher water absorption capability and promoted physical degradation, as observed in the surface topography. During the processing of biocomposites and throughout the hydrothermal ageing, a reduction of molecular weight due to chain scission was found. As a consequence, a faster formation of crystalline domains in the PLA matrix occurred the higher the amount of fibre was, which acted as a nucleating agent. Higher crystallinity was considered as a barrier against the advance of penetrant and a reduction in the diffusion coefficient was shown. The addition of coupling agent presented a different influence depending on the composition, showing an inflection point around 20% of sisal fibre.
Keywords: Biocomposites; Polylactide (PLA); Natural fibres; Sisal; Hydrothermal degradation; Water absorption;
Hydrolysable PBS-based poly(ester urethane)s thermoplastic elastomers by M. Fabbri; M. Gigli; R. Gamberini; N. Lotti; M. Gazzano; B. Rimini; A. Munari (223-231).
In this contribution a new class of aliphatic poly(butylene succinate) (PBS)-based poly(ester urethane)s has been synthesized and characterized from the molecular, thermal and mechanical point of view. Hydrolytic degradation studies under physiological conditions have been conducted to assess their biodegradation rate. To obtain copolymers showing both thermoplastic and elastomeric properties, the chain-linking strategy has been considered. In particular, two hydroxyl-terminated oligomers have been synthesized by melt polycondensation: poly(butylene succinate) (PBS), as a “hard segment”, and two poly(butylene adipate/diglycolate) P(BAmBDGn) random copolymers as a “soft segment”. The introduction of ether-linkages along the PBA chain permitted to depress its crystallinity degree and to enhance the wettability. Multiblock copolymers were finally obtained by chain extending with hexamethylene diisocyanate each P(BAmBDGn) copolymer with two different mass percentages of PBS: 30% and 50%. All copolymers maintained good thermal stability and were characterized by melting temperatures above 100 °C. Elastic modulus (E) and stress at break (σ b) varied with the chemical composition: the higher the PBS amount, the higher E and σ b. No yield and very high elongations at break were observed. Hydrolytic degradation studies highlighted an increase of the degradation rate with the increase of the BDG content.
Keywords: Thermoplastic elastomers; Poly(butylene succinate); Multiblock copolymers; Chain extension; Ether linkages; Hydrolytic degradation;
Effect of chain extenders on thermal and mechanical properties of poly(lactic acid) at high processing temperatures: Potential application in PLA/Polyamide 6 blend by Rattikarn Khankrua; Sommai Pivsa-Art; Hamada Hiroyuki; Supakij Suttiruengwong (232-240).
Poly(lactic acid) (PLA) is vulnerable to severe thermal degradation when it was processed at high temperature, especially above 200 °C. An undesired molecular weight reduction and weight loss caused by both hydrolysis and depolymerization reactions result in poor mechanical performance of final products. Thus, the aim of this work was to study the effect of chain extenders on the thermal and mechanical properties of PLA processed at high temperatures in a twin screw extruder having four different sets of temperature profiles. Two types of chain extenders, multifunctional epoxide (ECE) and polycarbodiimide (PCD) were used with the constant amount of 0.5 phr. All samples were characterized using GPC, MFI, DSC, TGA, FT-IR tensile and impact tester. The GPC results showed that the molecular weight (Mw) of processed PLA tended to decrease when increasing the processing temperatures and its molecular weight distribution (MWD) shifted towards lower molecular weights whereas Mw of all PLA added chain extenders samples increased and MWD exhibited bimodal distribution and slightly shifted towards higher molecular weight population. The addition of both chain extenders also improved elongation at break and impact strength. For processed PLA samples, these mechanical properties decreased. TGA thermograms of PLA added chain extenders samples showed the increase in onset and deflection temperatures when compared to processed PLA ones. The investigation of PLA based matrix (70%wt of total polymer) was also performed by blending with Polyamide 6 (30%wt of total polymer) with 0.5 phr of ECE or PCD in a twin screw extruder within the temperature profile of 170–250 °C. The blend with chain extenders proved to ease the effect of molecular weight reduction without sacrificing the mechanical properties. Both of PCD and ECE provided the improvement in modulus and tensile strength, especially elongation and impact strength for PLA/PA6/ECE blend. They increased by 92.2% and 65.1% respectively when compared to blend without ECE.
Keywords: Poly(lactic acid); Chain extenders; Polyamide; Thermal stability; Mechanical properties; High processing temperatures;
Polyurethane-urea substrates from rapeseed oil-based polyol for bone tissue cultures intended for application in tissue engineering by Milena Zieleniewska; Monika Auguścik; Aleksander Prociak; Piotr Rojek; Joanna Ryszkowska (241-249).
Porous polyurethane-urea substrates for bone tissue cultures were fabricated using two types of polyols: rapeseed oil-based and poly(ε-caprolactone)diol in various weight ratios. The materials were produced using hexamethylene diisocyanate, distilled water as a chain extender and sodium chloride particles as porogens. Polyurethane synthesis was performed using a prepolymer method in mass. Scanning electron microscopy was used to examine the porosity and differences in structure according to the various compositions of the reaction mixtures. Thermal degradation analysis was performed using thermogravimetric analysis techniques, and differential scanning calorimetry was used to determine phase-transition temperatures and thermal effects. Chemical composition and degree of phase separation of polyurethane-urea materials were examined by IR absorption spectroscopy. The bioactivity and degradation of synthesised materials were studied through testing in simulated body fluid. The obtained results lead to the conclusion that the polyurethane-urea materials based on rapeseed oil are very promising substrates for bone tissue cultures.
Keywords: Polyurethanes; Polyurethane-ureas; Scaffolds; Biomedical polymers; Porous polymer materials; Vegetable oils;
An in vitro crop plant ecotoxicity test for agricultural bioplastic constituents by L. Martin-Closas; R. Botet; A.M. Pelacho (250-256).
Plastic mulches are widely used in agriculture to improve production, mainly in vegetable crops. Their main drawback is the generation of residues that are hard to manage. Therefore the substitution of traditional plastics by renewable and biodegradable polymers is an environmentally friendly improvement. However, compounds released during (bio)degradation of the mulches may remain in the soil. Consequently, standard ecotoxicity tests are required to ensure the biomaterials' ecosafety. Unfortunately, ecotoxicity tests for terrestrial plants, and specifically for the plant species frequently cultivated with mulches, are poorly developed. Furthermore, most of these tests report seedling emergence and early plant growth, but germination and plant growth have different requirements, and plant growth inhibition by compounds not affecting germination has been frequently reported. Other limitations of ecotoxicity tests are related to environmental variability, interactions of soils/substrates with the chemicals, and to the limited monitoring of plant development over time, especially for roots.The aim of this work has been to develop an in vitro controlled system for testing the ecotoxicity of plastic constituents putatively delivered to the soil during mulch biodegradation on crop plants. Germination and growth of lettuce and tomato were monitored over time in response to adipic, succinic and lactic acids, and to 1,4-butanediol, in concentrations 5–500 mg l−1. Although germination was not influenced by most treatments, significant effects were manifested later in plant development. The sensitivity of the system was higher than in standard short-term assays. Results in lettuce and tomato were not substantially different, but indicative of the need to test the precise species targeted. Overall, adipic acid inhibited growth, succinic acid had no effect, and butanediol enhanced growth to some extent. Lactic acid requires further investigation. We highlight the convenience of the system for monitoring root development; roots were more sensitive to the chemicals than shoots and leaves. Proline is shown as a potential marker for ecotoxicoxicity. The in vitro system is proposed as a simple and reliable method to test for ecotoxicity in terrestrial plants.
Keywords: Adipic acid; Succinic acid; Lactic acid;1,4-butanediol; Lettuce; Tomato;
Effect of nanofiller's type on the thermal properties and enzymatic degradation of poly(ε-caprolactone) by Maria Nerantzaki; George Z. Papageorgiou; Dimitrios N. Bikiaris (257-268).
Poly(ε-caprolactone) (PCL) nanocomposites containing different types of montmorillonite, fumed silica nanoparticles or carbon nanotubes were prepared by the melt mixing technique. The nanofiller content was 2.5 wt% in all the materials. From the tensile properties study, it was found that the Young modulus increased in the nanocomposites, while the stress as well as the elongation at break decreased. The WAXD patterns of the materials showed no significant change in the crystal structure caused by the addition of the filler. The non-isothermal crystallization of the nanocomposites was studied with differential scanning calorimetry (DSC). In all cases, especially for MWCNTs, it was found that the addition of nanoparticles can increase the nucleation activity as well as the crystallization rates of the nanocomposites compared to those for neat PCL. This is a proof that the nanoparticles act as nucleating agents. From the enzymatic hydrolyses tests in the presence of lipases it was found that PCL has the highest mass loss from all tested samples and it is completely degraded after 8 days of hydrolysis. For the same time of hydrolysis, all nanocomposites showed lower mass loss, proving that addition of the nanoparticles decreased the hydrolysis rates of PCL. The delay depends on the used type of nanofillers. However, GC–MS analysis evidenced that nanofillers did not alter the hydrolysis mechanism of PCL, since for all the nanocomposites 6-hydroxy-hexanoic acid was the main byproduct.
Keywords: Polycaprolactone; Nanocomposites; Thermal properties; Enzymatic hydrolysis;
Characterization and degradation characteristics of poly(ε-caprolactone)-based composites reinforced with almond skin residues by Arantzazu Valdés García; Marina Ramos Santonja; Ana Beltrán Sanahuja; María del Carmen Garrigós Selva (269-279).
Poly(ε-caprolactone), PCL, degradation by microorganisms is a very interesting feature for its potential use in massive applications, such as food packaging. Blends of PCL with natural fibres, such as those from agricultural and food processing wastes, have proved effective by permitting a substantial reduction of the material costs, but also playing a role as reinforcement in mechanical properties. This study is focused on the evaluation of morphological, mechanical, thermal, barrier properties and degradation in composting environment of new bio-composites based on PCL and almond skin (AS) filler at different contents (0, 10, 20 and 30 wt%). Results showed a clear improvement in mechanical properties, corresponding to a gain in elastic modulus of 17% at 10 wt% particle loading. Lower melting and crystallization enthalpies and higher crystallinity values were obtained for bio-composites compared with neat PCL. Some decrease in thermal stability and increase in oxygen and water vapour barrier properties were also observed for composites with increasing filler content. PCL/AS composites showed higher biodegradability than pure PCL, which can be explained in terms of the depressed crystallization enthalpy of the polymer matrix and improved hydrophilicity. PCL-based composites reinforced with almond skin filler at 10 wt% loading have shown as promising environmentally-friendly materials for food packaging showing a high disintegration rate, increasing the added-value potential of agricultural wastes and reducing the packaging cost.
Keywords: Bio-composites; Degradation; Poly(ε-caprolactone); Almond skin; Reinforcement;
Inclusion of PLLA nanoparticles in thermosensitive semi-interpenetrating polymer networks by Nicoletta Rescignano; Rebeca Hernández; Ilaria Armentano; Debora Puglia; Carmen Mijangos; José Maria Kenny (280-287).
Novel nanocomposite semi-interpenetrating (semiIPN) polymer networks of poly(N-isopropylacrylamide) (PNIPAAm) and alginate (Alg-PNIPAAm), containing poly-L-lactide (PLLA) nanoparticles were prepared and morphological, thermal, chemical, thermomechanical and rheological properties were investigated.The successful incorporation of PLLA nanoparticles into the semiIPN gels was confirmed by field emission scanning electron microscope (FESEM) and infrared spectroscopy (FT-IR). FESEM microscopy also showed the different pore size and pore size distribution of the nanocomposite respect to the primary gel. The resulting morphology was related to the thermal and viscoelastic properties exhibited by the materials. The introduction of PLLA nanoparticles does not affect the thermal stability of the gel and does not modify the lower critical solution temperature (LCST), while interferes with the contraction behavior of the gel, leading to a different thermal expansion coefficient observed for the nanocomposite. Furthermore, rheological results suggest a different degree of crosslinking for the nanocomposite gel, due to the presence of PLLA nanoparticles that probably hinders the reaction of crosslinking of PNIPAAm. The prepared NPs-AlgPNIPAAm-semiIPN gels with thermosensitive and biodegradable properties are very interesting from both applied and fundamental perspectives and make this system a good candidate for practical application in drug delivery and controlled drug release.
Keywords: Hydrogel; Nanoparticles; Nanocomposite; Porous structure; Thermal stability;
Chemical recycling of poly(lactic acid) via controlled degradation with protic (macro)molecules by Andrzej Plichta; Paulina Lisowska; Anna Kundys; Agnieszka Zychewicz; Maciej Dębowski; Zbigniew Florjańczyk (288-296).
Designing of a new method of poly(lactic acid) chemical recycling leading to potentially useful products is the purpose of this paper. Controlled chemical degradation processes of commercial poly(lactic acid) in the presence of small molecules, such as diols, dipentaerythriol, diamines and adipic acid or oligo(ethylene glycol) as well as polyesterodiols were studied. The processes were found to be efficient and in the presence of a catalytical amount of tin(II) octanoate lead to the formation of homo- or block diol type copolymers or oligomers of lactic acid. Diamines appear to be the most efficient, even without catalyst at quite low temperature, whereas adipic acid eventually at 200 °C reacts with moderate efficacy. It is demonstrated that M w of the products is much lower with respect to that of poly(lactic acid). Degradation agents incorporate into the products' structures, however, in almost all cases some fraction of macro-α,ω-hydroxyacids is present in the samples, which seems to be unavoidable because of degradation mechanism and some residual moisture present in the polymers used. Products rich in ABA type triblock copolymers may be obtained by the degradation method presented utilizing macrodiols. The processes of poly(lactic acid) degradation with macrodiols can be carried out at temperatures of 120 °C or higher in solvent (e.g. xylene) or in bulk as well as an extruder. The reaction time depends on temperature and it is in the range from 30 min to 4 h. Aliphatic copolymers are homogeneous, whereas these containing aliphatic–aromatic macrodiols are of two-phases. The latter ones show different morphology based on composition. Triblock systems reveal multistage differential thermal analysis curves. Robust method of chemical recycling of poly(lactic acid) by controlled degradation with protic compounds is presented.
Keywords: Poly(lactic acid); Polylactide; Macrodiols; Triblock copolymers; Chemical degradation;
Plasticizers, antioxidants and reinforcement fillers from hazelnut skin and cocoa by-products: Extraction and use in PLA and PP by Daniele Battegazzore; Sergio Bocchini; Jenny Alongi; Alberto Frache (297-306).
The selective and serial extraction of natural additives from hazelnut skin and cocoa by-products has been carried out for giving a high-added value to poly(lactic acid) and poly(propylene) (PLA and PP). Through the proposed process, three fractions mainly containing plasticizers, antioxidants and reinforcement fillers have been consecutively separated. These have been subsequently characterized from the chemical and thermal point of view (assessed by infrared spectroscopy, differential scanning calorimetry and thermogravimetry), and then melt-blended with PLA or PP. Thus, the first fraction has been used for plasticizing PLA, the second one for UV-protecting PP, and the last one for reinforcing both matrices. The collected results by dynamic mechanical thermal analysis have shown that the first fraction partially plasticized PLA. The second fraction turned out to be consisting of UV absorbers as well as thermal stabilizers that increased PP oxidation induction time (of 30%) in the case of hazelnut skin, and PP thermal stability (of 26 °C in air) in the case of cocoa, respectively. The last fraction was capable to increase the storage modulus of PLA and PP up to 30 and 20% (with 30 wt.-% of filler content), respectively.
Keywords: Hazelnut; Cocoa; Thermal degradation; Photo-oxidation; Mechanical properties;
Disintegrability under composting conditions of plasticized PLA–PHB blends by M.P. Arrieta; J. López; E. Rayón; A. Jiménez (307-318).
The disintegration under composting conditions of films based on poly(lactic acid)–poly(hydroxybutyrate) (PLA–PHB) blends and intended for food packaging was studied. Two different plasticizers, poly(ethylene glycol) (PEG) and acetyl-tri-n-butyl citrate (ATBC), were used to limit the inherent brittleness of both biopolymers. Neat PLA, plasticized PLA and PLA–PHB films were processed by melt-blending and compression molding and they were further treated under composting conditions in a laboratory-scale test at 58 ± 2 °C. Disintegration levels were evaluated by monitoring their weight loss at different times: 0, 7, 14, 21 and 28 days. Morphological changes in all formulations were followed by optical and scanning electron microscopy (SEM). The influence of plasticizers on the disintegration of PLA and PLA–PHB blends was studied by evaluating their thermal and nanomechanical properties by thermogravimetric analysis (TGA) and the nanoindentation technique, respectively. Meanwhile, structural changes were followed by Fourier transformed infrared spectroscopy (FTIR). The ability of PHB to act as nucleating agent in PLA–PHB blends slowed down the PLA disintegration, while plasticizers speeded it up. The relationship between the mesolactide to lactide forms of PLA was calculated with a Pyrolysis–Gas Chromatography–Mass Spectrometry device (Py–GC/MS), revealing that the mesolactide form increased during composting.
Keywords: Poly(lactic acid); Poly(hydroxybutyrate); Blend; Biodegradable; Plasticizers;
Accelerated ageing of polylactide in aqueous environments: Comparative study between distilled water and seawater by Morgan Deroiné; Antoine Le Duigou; Yves-Marie Corre; Pierre-Yves Le Gac; Peter Davies; Guy César; Stéphane Bruzaud (319-329).
Pollution of nature by plastics is a major environmental problem and the challenge for the future is to manage the lifetime of polymers better. The aim of this study is to establish a baseline on degradation mechanism and degradation kinetics for lifetime prediction of polylactide (PLA) in a marine environment. The ageing of PLA was accelerated by raising temperature in distilled water, filtered and renewed seawater and natural seawater. Samples were immersed in distilled water for six months at different temperatures (25, 30, 40 and 50 °C) in order to evaluate the influence of temperature on PLA degradation kinetics and to predict lifetime. Then, samples were immersed in seawater both in the laboratory and at sea, in order to compare the effects of environment, marine organisms and salt, on degradation. The different degradation steps were followed by gravimetry, tensile tests, scanning electron microscopy (SEM), steric exclusion chromatography (SEC) and differential scanning calorimetry (DSC). In distilled water, accelerated ageing of PLA is complex with deviation from Fickian behaviour at higher temperature. Moreover, immersion in distilled water induces morphological changes, in particular holes, which are absent in seawater at 40 °C for the same immersion time. Indeed, seawater has little impact on the diffusion kinetics but affects M ∞ values, which are slightly lower compared to the distilled water uptake.
Keywords: PLA; Accelerated ageing; Hydrothermal ageing; Degradation;
Physicochemical properties of PLA lignin blends by Oihana Gordobil; Itziar Egüés; Rodrigo Llano-Ponte; Jalel Labidi (330-338).
Commercial alkali lignin (CL) and lignin extracted from almond shells by organosolv process (OL) were used for the preparation of blends with poly(lactic acid) (PLA) with different percentages (0.5, 1, 5, 10 and 20%) by extrusion method. Both lignins were acetylated to improve their compatibility with PLA. PLA/acetylated lignin blends exhibited greater compatibility than non-acetylated PLA/lignin. Characterization of lignins has been performed using HPLC, FT-IR, GPC, DSC and TGA. All lignins showed high purity. Acetylated lignins had lower T g and higher thermal stability than original lignins. Thermal and mechanical properties of different blends were investigated. Morphology before and after hydrolytic degradations of blends with 5% of different lignins were also investigated. The addition of acetylated lignin appears to prevent hydrolytic degradation of PLA. Lignin content increased the thermal stability of PLA but does not favor the crystallization of PLA. Maximum strength decreased with high percentages of originals lignins. However, PLA/acetylated lignin blends remains fairly constant, even at high percentages. In all cases, the elongation at break was increased.
Keywords: Lignin; Acetylation; Poly(lactic acid); Extrusion; Mechanical properties;