Search

The use of polymers for conservation of cultural heritage is related to the possibility to slow down or stop natural deterioration which, in many cases, corresponds to stopping the entrance of liquid water and to favour spontaneous water vapour removal. Unfortunately, hydrophobicity is generally favoured by surface roughness and thus competitive with transparency. It is therefore important to find an optimal balance hydrophobicity, transparency and durability (especially to photooxidation). However, polymers typically used for applications in this field come from non-renewable resources and are not biodegradable. In this work, the mechanical, structural and optical properties of PLA, PBAT and a PBAT/PLA blends, as well as surface properties and water vapour permeability, were investigated before and after exposure to UV irradiation, in order to evaluate their durability and suitability for conservation of cultural heritage.

It is well known that the need for more environmentally friendly materials concerns, among other fields, the food packaging industry. This regards also, for instance, nets used for agricultural product (e.g., citrus fruits, potatoes) packaging. These nets are typically manufactured by film blowing technique, with subsequent slicing of the films and cold drawing of the obtained strips, made from traditional, non-biodegradable polymer systems. In this work, two biodegradable polymer systems were characterized from rheological, processability, and mechanical points of view, in order to evaluate their suitability to replace polyethylene-based polymer systems typically used for agricultural product net manufacturing. Furthermore, laboratory simulation of the above-mentioned processing operation paths was performed. The results indicated a good potential for biodegradable polymer systems to replace polyethylene-based systems for agricultural product packaging.

The use of biodegradable polymers is increasingly attracting interest over the last years, since they can reduce the environmental effects related to disposal of traditional plastics and, in general, the use of fossil, non-renewable resources. One of the most promising applications is represented by fibers production. However, the orientation and the crystallinity degrees can significantly affect the mechanical properties. Therefore, it is of interest to investigate on the optimum processing conditions, in order to improve the mechanical properties. In particular, while crystallinity can be slightly modified by the processing, orientation can be significantly improved. In this work, the effects of hot stretching on the mechanical and structural properties of fibers made from two different families of biodegradable blends were investigated. The orientation proved to significantly change the mechanical properties, and it was shown that factors such as the different relaxation times, the different crystallization temperatures and the cooling rate can give opposite effects in the three investigated polymer systems with significant consequences on the mechanical behaviour of the fibers. In particular, the behaviour during fiber production in hot stretching, and the orientation mechanisms were studied and explained on the basis of rheological and thermal properties of the polymers.

Films for agricultural or packaging applications are typically made of low density polyethylene (LDPE). They are produced through the film blowing process, which requires the use of polymers with suitable rheological properties. Furthermore, the short shelf-life which is often related to many packed products leads to huge amounts of plastic-based wastes. This suggests the use of biodegradable and/or compostable polymers in replacement for traditional ones. To this regard, only few data exist on the rheological properties of biodegradable polymers undergoing film blowing processing. In this work, a detailed investigation on the rheological, mechanical and processability behaviour of some biodegradable polymers (originating from MaterBi® and Bioflex® commercial groups) was carried out, in order to assess their suitability to industrial-scale film blowing by direct comparison with a traditional non-biodegradable polymer (LDPE). Rheological tests under shear and non-isothermal elongational flow allowed to find out the two most suitable polymer grades. The film blowing production operations at different draw and blow-up ratios (from 2.5 to 3.5) showed that the two samples are suitable for industrial scale operations. Results from tensile and impact tests indicated that the two selected polymers exhibit significantly different mechanical properties (up to 10–15%).

The rising concerns in terms of environmental protection and the search for more versatile polymer-based materials have led to an increasing interest in the use of polymer composites filled with natural organic fillers (biodegradable and/or coming from renewable resources) as a replacement for traditional mineral inorganic fillers. At the same time, the recycling of polymers is still of fundamental importance in order to optimize the utilization of available resources, reducing the environmental impact related to the life cycle of polymer-based items. Green composites from biopolymer matrix and wood flour were prepared and the investigation focused on several issues, such as the effect of reprocessing on the matrix properties, wood flour loading effects on virgin and reprocessed biopolymer, and wood flour effects on material reprocessability. Tensile, Dynamic-mechanical thermal (DMTA), differential scanning calorimetry (DSC) and creep tests were performed, pointing out that wood flour leads to an improvement of rigidity and creep resistance in comparison to the pristine polymer, without compromising other properties such as the tensile strength. The biopolymer also showed a good resistance to multiple reprocessing, the latter even allowed for improving some properties of the obtained green composites.

Polymer blends of incompatible components need to undergo compatibilization, in order to give rise to a blend with good physical properties. At the same way, polymer/clay nanocomposites show this problem because of different chemical nature of the polymer matrix and of the clay. Compatibilization is therefore more necessary if an incompatible polymer blend is filled with an organomodified clay in order to give a final material with good properties. In this work, a polyethylene/polyamide 6 blend filled with an organomodified clay has been compatibilized with a maleic anhydride grafted SEBS (styrene-ethylene-butylene-styrene) copolymer and a glicidylmethacrylate-ethylene copolymer. The results show that compatibilization improves the mechanical properties in terms of elongation at break, as well as the rheological properties under nonisothermal elongational flow; furthermore, an unexpected effect has been found, since going from the isotropic to the anisotropic material, a fragile-ductile transition occurs, with a significant increase of the elongation values, while a small reduction of the elastic modulus was found, because of the lower crystallinity in comparison to isotropic samples. POLYM. COMPOS., 36:992–998, 2015. © 2015 Society of Plastics Engineers

Thermomechanical degradation of nanocomposites is a topical issue that has not been fully investigated as demonstrated by the low number of papers available in the literature regarding this spe- cific aspect. In particular, with regards to low density polyethylene/clay nanocomposites, the degrada- tion behavior is very complex since it involves the degradation paths of both the polymer matrix and the organomodified nanoclay. In the present work, the effects of mechanical stress and temperature on the thermomechanical behavior of PE-LD/organomodified clay nanocomposites and the degradation paths were investigated by rheological, FT-IR and mechanical methods. The results have shown that the thermomechanical degradation mechanisms are very complex, involving several phenomena such as chain scission, branching, recrystallization and crosslinking, degradation of the organomodified clay and interaction between the degradation products of both system components. These interactions between the degradation products of the organomodifier and the polymer matrix can deeply influence the final behavior of the nanocomposite in a way which is similar to what usually happens in polymer blends.

The recent increasing interest towards biodegradable polymers has favoured the investigation on these systems, showing also their limits. On the other hand, the success achieved by nanocomposites has fostered the search for new systems where the polymer matrix is biodegradable. The final properties can depend on a number of factors, including the biodegradable polymer used as well as the nanosized filler, their mutual compatibility, the filler dispersion and the processing conditions. In this work, nanocomposites based on a starch-derived matrix and three different lamellar silicates were prepared, and the effects of the elongational flow on the dispersion, the improvement of intercalation/exfoliation and the possible aligning of the nanosilicate particles along the flow direction was investigated. Rheological, morphological and tensile tests showed that the properties were significantly different upon varying the compatibility between the polymer matrix and the nanofiller, as well as the draw ratio and therefore the orientation degree.

The production of many items, in particular for food packaging applications, is based on foam extrusion and thermoforming. These operations require the use of polymers which can grant some specific rheological properties, both under shear and elongational flow. In this work, the behavior of some biodegradable polymers [Mater-Bi® and poly(lactic acid)] under shear and non-isothermal elongational flow was investigated and compared with a traditional, non-biodegradable polymer, in order to assess their suitability for industrial-scale foam extrusion and thermoforming. The rheological characterization evidenced the differences between the different biodegradable polymers and the reference polystyrene (PS), as well as the effect of humidity on their main rheological properties. This can be of great interest in helping to find an optimum solution in replacing PS for the production of food packaging items.

Polymer nanocomposites are currently a topic of great interest. The increasing importance they are gaining also in the standpoint of industrial applications, is giving concerns regarding their environmental stability and, in general, their behaviour in outdoor applications, under direct solar irradiation. Papers available in the literature have highlighted the different influences of different nanosized fillers, in particular clay-based nanofillers; however, few data are available regarding other nanosized fillers. Furthermore, the research on polymer nanocomposites has clearly pointed out that the use of compatibilizers is required to improve the mechanical performance and the dispersion of polar fillers inside apolar polymer matrices, especially when complex mechanisms such as intercalation and exfoliation, typical of clay-filled nanocomposites, are involved. In this work, the photo-oxidation behaviour of polypropylene/clay and polypropylene/calcium carbonate nanocomposites containing different amounts of maleic anhydride grafted polypropylene (PPgMA) and subjected to accelerated weathering, was investigated. The results showed significant differences between the two nanofillers and different degradation behaviours in presence of the compatibilizer. In particular, PPgMA modified the dispersion of the nanofillers but, on the other hand, higher amounts proved to lead to the formation of some heterogeneities. Furthermore, PPgMA proved to positively affect the photo-oxidation behaviour by decreasing the rate of formation of the degradation products. © BME-PT.

Purpose Biodegradable polymers are currently gaining importance in several fields, because they allow mitigation of the impact on the environment related to disposal of traditional, nonbiodegradable polymers, as well as reducing the utilization of oil-based sources (when they also come from renewable resources). Fibers made of biodegradable polymers are of particular interest, though, it is not easy to obtain polymer fibers with suitable mechanical properties and to tailor these to the specific application. The main ways to tailor the mechanical properties of a given biodegradable polymer fiber are based on crystallinity and orientation control. However, crystallinity can only marginally be modified during processing, while orientation can be controlled, either during hot drawing or cold stretching. In this paper, a systematic investigation of the influence of cold stretching on the mechanical and thermomechanical properties of fibers prepared from different biodegradable polymer systems was carried out. Methods Rheological and thermal characterization helped in interpreting the orientation mechanisms, also on the basis of the molecular structure of the polymer systems. Results and conclusions It was found that cold drawing strongly improved the elastic modulus, tensile strength and thermomechanical resistance of the fibers, in comparison with hot-spun fibers. The elastic modulus showed higher increment rates in the biodegradable systems upon increasing the draw ratio.

Polymer nanocomposites and their behavior have been widely investigated by several paths, including mechanical, rheological, and permeability tests, finding that several parameters (such as the polymer matrix, the nanofiller, their amounts, the presence of compatibilizers, processing parameters, etc.) can influence the main properties. However, less information is available regarding the creep response of polymer nanocomposites; in particular, few or no data are reported about the combined effect of different loads and different temperatures. In this article, the creep behavior of a low density polyethylene/organomodified clay nanocomposite has been investigated. The characterization of viscoelastic response has taken into account both the effects of applied load and temperature, which are often considered separately. Dynamic–mechanical and structural analysis was also performed in order to get a deeper understanding of the involved phenomena. The nanocomposite showed lower creep deformations (up to ∼20%) and the relative differences with the neat polymer matrix were found to be increasing upon increasing the applied load (up to ∼24%) and the temperature (up to ∼38%). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44180.

Polymer composites filled with natural organic fillers have gained a significant interest during the last few years, because of several advantages they can offer compared with properties of inorganic-mineral fillers. However, these composites (based, in most cases, on polyolefins) often show a reduction in some mechanical properties. This is mainly due to the problems regarding dispersion of the polar filler particles in the non-polar polymer matrix and their interfacial adhesion with polymer chains. In this work, polypropylene-wood flour composites were prepared and the effect of the addition of a maleated polypropylene was investigated. The two materials were compounded by an industrial co-rotating twin screw extruder, with two different compositions, without and with addition of Licomont AR504® (maleic anhydride-grafted polypropylene wax). The extruded material was then compression molded, which provided the specimens for tensile and impact tests. Water uptake was measured; the morphology of the fracture surfaces of the samples coming out from mechanical tests was investigated through SEM analysis. Rheological characterization was carried out as well. The addition of the adhesion promoter allowed a decrease in water uptake; mechanical properties were improved as well, especially elastic modulus and tensile strength; impact strength increased in the case of unnotched samples, while notched ones did not show remarkable differences. SEM analysis of the fracture surfaces also showed an overall change in the morphology as a consequence of the utilization of the adhesion promoter

Polymer based nanocomposites are increasingly attracting interest from academia and industry, and the use of polymer blends as matrices greatly increase their potential field of application. In order to improve their characteristics, the use of compatibilizers acting on the blend components is mandatory. However, this also leads to rising concerns regarding the behaviour of polymer blend based nanocomposites upon being subjected to photo-oxidative degradation. It is known that morphology can deeply influence the photo-oxidative behaviour, and this can be therefore deeply influenced by the blend components and by the use of compatibilizers. In this work, polymer blend nanocomposites, based on low density polyethylene and polyamide 6 have been prepared, containing organically modified clay as nanosized filler and two different functionalized polymers as compatibilizers, and processed in a film blowing operation in order to evaluate the effect of the compatibilization on photo-oxidation. The presence of the compatibilizer significantly improves the photo-resistance of the blend, while this improvement is less relevant in the nanocomposites since the photo-oxidation rate seems to be mainly dependent on the clay content and its direct effects on the photo-oxidative phenomena.

Polymer nanocomposites have continually attracted increasing interest over the last decade, due to significant improvements they can offer compared to neat polymer matrices. However, the final morphology of a nanocomposite, determined by several variables, can significantly influence the macroscopic properties of the final product. Therefore, it is important to study the interactions between processing, morphology, structure and rheological properties, and the suitability of existing models in order to predict the system's behaviour with change of the main processing variables. In this work, the applicability of a predictive theory based on the Wu model was formulated and proposed in order to predict the morphology of nanocomposite systems. This theory allows description of a polymer matrix - lamellar filler system, provided that the interactions between the two components and the processing are known. In particular, a lamellar filler has been considered as a deformable second component of a blend, with its behaviour depending on the processing and on the interactions with the polymer matrix. This allowed analyzing different behaviour for the systems, due to the different polarity of the matrix, which may lead to a classification of polymer nanocomposites in two or more families, according to their different matrix polarities.

Polymer blends of incompatible components need to be compatibilized to give rise to a blend with good properties. At the same way, polymer/clay nanocomposites show the same problem because of different chemical nature of the polymer matrix and of the clay. Compatibilization is then necessary if an incompatible polymer blend is filled with an organomodified clay. In this work a polyethylene/polyamide 6 blend filled with an organomodified clay has been compatibilized with a maleic anyhidride grafted SEBS (styrene-ethylene-butylene-styrene) copolymer and a glicidylmethacrylate-ethylene copolymer. The results show that compatibilization improves the mechanical properties in terms of elongation at break; furthermore, an unexpected effect has been found, since going from the isotropic to the anisotropic material, a fragile-ductile transition occurs, with a significant increase of the elongation values.

Poly(ethylene terephthalate) (PET) is one of the most used commodity polymers, especially for food and beverage applications, and its recycling is of great importance because of the possible use in the textile and construction industries. On the other hand, the interest in biodegradable polymers has led, in recent years, to the use of materials such as poly(lactic acid) (PLA) also in the food and beverage industry. The presence of small amounts of PLA in the PET waste can significantly affect the post-consumer recycling process. In this work, the effect of the presence of small amounts of PLA on the recycling of PET bottles is investigated by rheological, mechanical, morphological and thermogravimetric analysis. The results indicate that this presence can significantly affect the rheological properties under non-isothermal elongational flow, while the mechanical properties were considerably affected only in some circumstances and the thermal stability was not significantly modified.

Interest in biocomposites (lignocellulosic filled biopolymers) started in the 90s, due to environmental advantages, related to the full biodegradability of both matrix and filler, economical issues (organic fillers usually come from sawmill or agriculture wastes) and aesthetical issues (wood filled biopolymers could be particularly pleasant if used for indoor furnishing and automotive interior). In this work, a method for a systematic study of the properties of Mater-Bi®/wood flour composites is presented. A two-level full factorial model was built. It allows investigating the effects of multiple operative variables on the observed properties, their contributions, their optimal combinations and their possible interactions. Several composites were prepared in a batch mixer, by changing the processing conditions like filler aspect ratio, filler content, mixing speed, mixing temperature and polymer pre-treatment. The model allowed detecting the statistically significant variations of mechanical properties like the elastic modulus, the impact strength and the heat deflection temperature upon changing the process variables. All these properties are of interest in the view of the possible final applications of these composites. It was found that the most influencing variable on the elastic modulus is the filler content, even if the pre-treatment of the matrix and the mixing speed showed to have some influence too. The impact strength was mainly influenced by the filler aspect ratio and the mixing speed, while only a moderate statistical significance was attributed to the temperature and the pre-treatment. The heat deflection temperature proved to be statistically significantly influenced by the filler content and by its size.nterest in biocomposites (lignocellulosic filled biopolymers) started in the 90s, due to environmental advantages, related to the full biodegradability of both matrix and filler, economical issues (organic fillers usually come from sawmill or agriculture wastes) and aesthetical issues (wood filled biopolymers could be particularly pleasant if used for indoor furnishing and automotive interior). In this work, a method for a systematic study of the properties of Mater-Bi®/wood flour composites is presented. A two-level full factorial model was built. It allows investigating the effects of multiple operative variables on the observed properties, their contributions, their optimal combinations and their possible interactions. Several composites were prepared in a batch mixer, by changing the processing conditions like filler aspect ratio, filler content, mixing speed, mixing temperature and polymer pre-treatment. The model allowed detecting the statistically significant variations of mechanical properties like the elastic modulus, the impact strength and the heat deflection temperature upon changing the process variables. All these properties are of interest in the view of the possible final applications of these composites. It was found that the most influencing variable on the elastic modulus is the filler content, even if the pre-treatment of the matrix and the mixing speed showed to have some influence too. The impact strength was mainly influenced by the filler aspect ratio and the mixing speed, while only a moderate statistical significance was attributed to the temperature and the pre-treatment. The heat deflection temperature proved to be statistically significantly influenced by the filler content and by its size.