Blend Partners Research Articles

Electron Beam-Induced Compatibilization of PLA/PBAT Blends in Presence of Epoxidized Soybean Oil.

Blending of polymers can enhance performance of plastics and can give the opportunity to broaden the application fields. Especially the brittleness of poly(lactic acid) (PLA) is an issue, that is often addressed by blending it with soft polymers like poly(butylene adipate terephthalate) (PBAT). The immiscibility of those two polymers leads to limited properties of the blend. This study aimed to examine the application of electron-beam treatment with the implementation of a compatibilizing agent. PLA and PBAT were compounded with the addition of epoxidized soybean oil (ESBO) in different ratios and extruded into flat films. These were treated with electron beams at irradiation doses ranging from 12.5 to 100 kGy. The films thus produced were characterized by differential scanning calorimetry, size exclusion chromatography, scanning electron microscopy and tensile testing. A significant change in the glass transition temperatures of the blend partners was observed, as well as a substantial increase in elongation at break, even in PLA-rich compositions. These findings indicate improved compatibilization. Furthermore, the use of epoxidized soybean oil showed a changed extraction behavior of PBAT, indicating a formed binding to PLA. The results show that electron-beam treatment can significantly improve the compatibility between different polymers in blends, leading to enhanced mechanical and thermal properties.

EXTERIORIZATION OF QUANTITATIVE TRAITS WITH INFLUENCE ON FORAGE YIELD IN ITALIAN RYEGRASS

The spread of Italian ryegrass culture worldwide is due to its large yield capacity, superior feed quality and the fact that it is an ideal blending partner. The Italian ryegrass (Lolium multiflorum Lam.) Is a very valuable forage plant with wide possibilities of use in animal feed (green mass, hay, silo) and has a very high capacity to adapt to different types of soils and climates. In this context, the aim of this research is to evaluate the differences between the growth traits and productivity of three varieties of Lolium multiflorum Lam. var. Westerwoldicum, sown in autumn in an area with cold winters. Two alternative tetraploid varieties (Linos and Ivan) and an alternative diploid variety - Sprint (Catalogo-zanandrea-sementi-en.pdf), recommended for green mass and silo, were used as biological material. In order to evaluate the three varieties, the basic green mass feed yield elements (number of tillers, their height and the weight of the bunch) and the green mass yield at the first harvest were taken into account. The results of the research show that the Linos variety recorded the highest weight of the bunch based on the large number of tiller and the height of the tillers. The variations are much larger between the Linos and Ivan varieties based on the number of tillers. The green mass yields of the three Italian ryegrass varieties studied are directly influenced by the values of the yield / bunch traits. Thus, the largest yield of green mass at the first harvest, of 28.9 t.ha-1, was also registered for the Linos variety. This study has a special practical importance, bringing a plus in the technology of cultivation of Italian ryegrass sown in autumn in the conditions of cold winters.

Ensuring patient safety by rational choice of color masterbatch for medical device applications—A case study investigating the properties of an ABS/SAN blend colored by different masterbatches based on styrenic polymers

AbstractThe coloration of plastics is an important quality feature of medical devices, and it is most frequently done by using masterbatches. This study investigates the influence of masterbatches with different carrier resins on the impact resistance and the morphology of an acrylonitrile‐butadiene‐styrene (ABS)/styrene‐acrylonitrile (SAN) blend. The experimental results were compared with thermodynamical models based on Hansen and Flory–Huggins theory. The models, as well as notched impact testing, indicated strong immiscibility and incompatibility when using a masterbatch carrier based on polystyrene (PS). Immiscibility was confirmed by morphology studies that revealed the formation of PS‐droplets with increasing masterbatch content. Masterbatches based on ABS and SAN showed no significant impact and theoretical calculations were in good accordance with mechanics and morphology. The proposed theoretical calculation of solubility between blend partners potentially allows a prediction for selecting a suitable masterbatch carrier.

(A04 Best Poster Award Winner) Formation Mechanism and Stability of Solid Electrolyte Interphases in Linear Carbonate-Based Electrolytes

Broad application of lithium batteries, necessitates improvements in their safety, cycle life, durability and energy density. Clear understanding of the electrode/electrolyte interfaces is one of the important factors in designing batteries with enhanced performance. Linear organic solvents are extensively used in electrolytes of lithium batteries to reduce viscosity and melting temperature of cyclic carbonates. However, these organic compounds are not stable in contact with anode, leading to decomposition of the electrolyte and formation of Solid Electrolyte Interphase (SEI). Although SEI is proven to be one of the most important parts of batteries, its structural complexity, mechanism of formation, and properties are not completely understood yet. In this work, we consider mechanism of formation and stability of SEIs composed of redox products of linear carbonate solvents. So far, the main focus of research was on decomposition products of cyclic carbonates. In case of linear carbonates, the SEI stability consideration is limited to the systems being in DMC solvent and to the best of our knowledge, there are no theoretical investigations on linear carbonate-based SEIs formation mechanism and properties.In this work, we study Lithium Methyl Carbonate (LMC), Lithium Ethyl Carbonate (LEC) and Lithium Propyl Carbonate (LPC), which are single-electron reduction products of carbonate solvents in contact with the electrode, in their corresponding solvents being Dilithium Methyl Carbonate (DMC), Dilithium Ethyl Carbonate (DEC) and Dilithium Propyl Carbonate (DPC), respectively (Figure 1). Our aim is to chemically, kinetically, and thermodynamically study the aggregation, formation and stability of SEI layer in these systems from experimental, Molecular Dynamics (MD) simulation and Density Functional Theory (DFT) calculation points of view. Our study indicates that in LMC/DMC mixture LMC molecules have strong tendency to self-assemble and have low barriers to undergo second-electron reduction to form stable Li2CO3. Stable SEI was also observed in LPC/DPC as well, which is believed to be a result of slow dynamics of larger molecules and therefore increased possibility of the second-electron reduction near electrode surface. In the LEC/DEC system, however, we did not observe a stable SEI formation due to low tendency of LEC molecules to self-assemble, low electronic affinity coupled with high energy barrier for possible second electron reduction reaction. Therefore, our work illustrates that the selection of the linear carbonate as a blending partner for cyclic carbonates, might have an important impact on the ability of electrolyte to form stable and compact SEI layer. Figure 1

Properties of Styrene-Maleic Anhydride Copolymer Compatibilized Polyamide 66/Poly (Phenylene Ether) Blends: Effect of Blend Ratio and Compatibilizer Content.

Two different blend ratios of polyamide 66 (PA66) and poly (2,6-dimethyl-1,4-phenylene ether) (PPE) (60/40 and 40/60 w/w) were produced via melt mixing. A styrene–maleic anhydride copolymer (SMA) was utilized at various contents from 2.5–15 wt% to compatibilize the immiscible blend system. The influence of SMA content and blend ratio was investigated based on (thermo-) mechanical and morphological properties of the PA66/PPE blends. Correlations between the interaction of SMA with the blend partners were established. For 60/40 blends, a droplet-sea morphology was visualized by transmission electron microscopy, wherein no major changes were seen upon SMA addition. In the case of 40/60 blends, strong coalescence was found in the binary blend. Up to 5 wt% SMA, the coalescence was inhibited by the interfacial activity of SMA, whereas 10 wt% SMA initiated a disperse-to-co-continuous transition, which was completed at 15 wt% SMA. An enhancement of tensile properties was achieved for all blends possessing SMA, where the maximum concentration of 15 wt% resulted in the highest elongation at break and tensile strength values. The relative improvement of the tensile properties was higher with the PPE-rich blend (40/60) which was attributed to a partial emulsification of the PPE phases forming a bimodal PPE domain size distribution with nano-droplets in the range of 60–160 nm.

Formation Mechanism and Stability of Solid Electrolyte Interphases in Linear Carbonate-Based Electrolytes

Broad application of lithium batteries, necessitates improvements in their safety, cycle life, durability and energy density. Clear understanding of the electrode/electrolyte interfaces is one of the important factors in designing batteries with enhanced performance. Linear organic solvents are extensively used in electrolytes of lithium batteries to reduce viscosity and melting temperature of cyclic carbonates. However, these organic compounds are not stable in contact with anode, leading to decomposition of the electrolyte and formation of Solid Electrolyte Interphase (SEI). Although SEI is proven to be one of the most important parts of batteries, its structural complexity, mechanism of formation, and properties are not completely understood yet. In this work, we consider mechanism of formation and stability of SEIs composed of redox products of linear carbonate solvents. So far, the main focus of research was on decomposition products of cyclic carbonates. In case of linear carbonates, the SEI stability consideration is limited to the systems being in DMC solvent and to the best of our knowledge, there are no theoretical investigations on linear carbonate-based SEIs formation mechanism and properties.In this work, we study Lithium Methyl Carbonate (LMC), Lithium Ethyl Carbonate (LEC) and Lithium Propyl Carbonate (LPC), which are single-electron reduction products of carbonate solvents in contact with the electrode, in their corresponding solvents being Dilithium Methyl Carbonate (DMC), Dilithium Ethyl Carbonate (DEC) and Dilithium Propyl Carbonate (DPC), respectively (Figure 1). Our aim is to chemically, kinetically, and thermodynamically study the aggregation, formation and stability of SEI layer in these systems from experimental, Molecular Dynamics (MD) simulation and Density Functional Theory (DFT) calculation points of view. Our study indicates that in LMC/DMC mixture LMC molecules have strong tendency to self-assemble and have low barriers to undergo second-electron reduction to form stable Li2CO3. Stable SEI was also observed in LPC/DPC as well, which is believed to be a result of slow dynamics of larger molecules and therefore increased possibility of the second-electron reduction near electrode surface. In the LEC/DEC system, however, we did not observe a stable SEI formation due to low tendency of LEC molecules to self-assemble, low electronic affinity coupled with high energy barrier for possible second electron reduction reaction. Therefore, our work illustrates that the selection of the linear carbonate as a blending partner for cyclic carbonates, might have an important impact on the ability of electrolyte to form stable and compact SEI layer. Figure 1. Carbonate solvents and components studied in this work. Figure 1

Hydroxypropyl-modified and organosolv lignin/bio-based polyamide blend filaments as carbon fibre precursors’

Hydroxypropyl-modified lignin (TcC) and organosolv lignin (TcA) were melt blended with two types of bio-based polyamides (PA) (PA1010 and PA1012) before being melt spun into filaments. With a lignin/bio-PA ratio 50/50 wt%, the filaments could be continuously produced and spooled having tensile strengths ≥ 20 MPa and moduli ≥ 500 MPa. The influence of each polyamide blended with each lignin on structural (FTIR), thermal (DSC, TGA, DMA), mechanical, rheological and morphological properties of the resultant extrudates and/or filaments was studied. The melting point of each polyamide was reduced in the presence of TcA and TcC lignin, and shifts in the glass transition temperature (Tg) and FTIR characteristic peaks occurred, which suggests that the selected polyamides and lignins are compatible with each other. The improved lignin/polyamide compatibilities were further supported by Pukanszky interfacial adhesion modelling. Despite the evidence for strong interactions, heterogeneous morphologies were observed in the resulting blends and scanning electron microscopy was used to determine dispersed lignin domain sizes which decreased when stronger lignin/polyamide interactions resulted. As a possible indicator of carbonization efficiencies, blends were subjected to a simulated stabilization/cross-linking process and subsequent TGA char residues were higher than those theoretically calculated at 880 °C, indicating that the bio-polyamide acted as a char-promoting agent for the lignin besides being a good blending partner. Overall, this study has indicated that the developed lignin/bio-polyamide filaments have potential as melt-extrudable precursors for carbon fibre production.

Influence of Particle Size and Phase Connectivity on the Fracture Behavior of PA6/EOR Blends

Structure–property relations between the blend morphology and the fracture mechanical behavior of immiscible polyamide 6/ethylene‐octene copolymer (PA6/EOR) blends are investigated. The influence of a moisture uptake of the PA6 on the blend behavior is also demonstrated. Different blend formulations lead to different blend morphologies, which vary in particle sizes, interparticle spacing, and intensity of the phase connectivity between the blend partners. The intensity of the phase connectivity is described by the rheological behavior. The morphology, defined by the particle size and the calculated interparticle spacing, is analyzed optically by a scanning electron microscope. The shift of the glass transition temperature of the blends due to moisture uptake is demonstrated via dynamical mechanical analyses. All parameters are linked to the fracture mechanical properties determined by the method of the essential work of fracture. By means of the method of the essential work of fracture it is shown that the toughness increase by a given material combination and a constant soft phase amount depends only on the particle size. However, a basic requirement is always strong phase connectivity between the blend partners. Thus, by a given material combination the smaller the soft phase particles within the matrix, the higher the increase in toughness. A moisture uptake does influence the blend properties in many ways and also leads to a change in the fracture behavior. Therefore, it is not possible to predict the fracture mechanical behavior of hydrophilic blends from one condition state to another.

‘Sunbelt’ as a Possible ‘Concord’ Juice Grape Partner in a Warming World

The juice grape (Vitis labruscana) cultivar Sunbelt has been reported to ripen more uniformly than the cultivar Concord in warm climates; thus, ‘Sunbelt’ might be useful as either a blending partner with or replacement for ‘Concord’ as global climate change intensifies. We conducted a 4-year field trial to evaluate ‘Sunbelt’ alongside ‘Concord’ in arid southeastern Washington. ‘Concord’ yields were on the average 57% higher than ‘Sunbelt’ yields because ‘Concord’ vines produced more shoots of higher fruitfulness and consequently had more clusters. The 31% larger berries of ‘Sunbelt’ were insufficient to compensate for its lower cluster number. Conversion from hand pruning to minimal (machine) pruning had no consistent influence on yield in either cultivar. Juice soluble solids, titratable acidity (TA), red color intensity, and color hue were significantly higher in ‘Sunbelt’ than ‘Concord’, whereas pH and potassium were often similar. Both cultivars cold acclimated in autumn and deacclimated in spring, but hardiness varied during winter depending on prevailing temperatures. With some exceptions, the two cultivars had similar bud, phloem, and xylem hardiness. When differences were significant, ‘Sunbelt’ was 1 to 4 °C less hardy than ‘Concord’ and also tended to deacclimate more readily in spring. The results from this study indicate that ‘Sunbelt’ shows promise as a blending partner with or an alternative to ‘Concord’ for warm vineyard sites or growing seasons even in regions with cold winters.

Morphology Formation in PC/ABS Blends during Thermal Processing and the Effect of the Viscosity Ratio of Blend Partners

Morphology formation during compounding, as well as injection molding of blends containing 60 wt % polycarbonate (PC) and 40 wt % polybutadiene rubber-modified styrene-acrylonitrile copolymers (ABS), has been investigated by transmission electron microscopy (TEM). Profiles of the blend morphology have been recorded in injection-molded specimens and significant morphology gradients observed between their skin and core. A <10 µm thick surface layer with strongly dispersed and elongated nano-scale (streak-like) styrene acrylonitrile (SAN) phases and well-dispersed, isolated SAN-grafted polybutadiene rubber particles is followed by a 50–150 µm thick skin layer in which polymer morphology is characterized by lamellar SAN/ABS phases. Thickness of these lamellae increases with the distance from the specimen’s surface. In the core of the specimens the SAN-grafted polybutadiene rubber particles are exclusively present within the SAN phases, which exhibit a much coarser and less oriented, dispersed morphology compared to the skin. The effects of the viscosity of the SAN in the PC/ABS blends on phase morphologies and correlations with fracture mechanics in tensile and impact tests were investigated, including scanning electron microscopy (SEM) assessment of the fracture surfaces. A model explaining the mechanisms of morphology formation during injection molding of PC/ABS blends is discussed.

Recycling of blends made of polypropylene and an iron-based oxygen scavenger – Influence of multiple extrusions on the polymer stability and the oxygen absorption capacity

An often used oxygen scavenger is a blend of iron powder and additives dispersed in a polymer carrier matrix. It is applied as an additive for separate layers of multilayer film structures which are produced by coextrusion. Not much is known about the influence of multiple extrusions, for example during recycling processes, of these materials on polymer properties, film properties and process stability. Therefore the aim of this study was to assess these issues. The focus was on polypropylene because it is a common blend partner for iron-based oxygen scavenger additives. Pure polypropylene and blends of polypropylene with approximately 20 wt.-% iron-based oxygen scavenger additive (SHELFPLUS® O2 2710) were extruded up to ten times at two temperature profiles (T1: 160–230 °C; T2: 210–300 °C). Polymer degradation was evaluated by different means of measurement: MFR, DSC, colorimetry, IR-spectroscopy and oxygen absorption. The results indicate that polypropylene and polypropylene with dispersed oxygen scavenger degrade by the impact of extrusion which can be seen by increased MFR and crystallinity and color changes. Furthermore the iron particles did undergo changes regarding color and oxygen scavenging capacity. The absorption capacity at 23 °C was reduced by one third from 39 to 48 mg oxygen per one gram scavenger additive after one extrusion to 26–35 mg oxygen per one gram scavenger additive after 9 and 10 extrusion cycles, respectively. Overall the iron based oxygen scavenger has a lower impact on degradation than the temperature and the number of extrusions.

Mechanical characterization and modelling of the temperature-dependent impact behaviour of a biocompatible poly(L-lactide)/poly(ε-caprolactone) polymer blend

Poly(ε-caprolactone) (PCL) is a ductile, bioabsorbable polymer that has been employed as a blend partner for poly(L-lactic acid) (PLLA). An improvement of the material strength and impact resistance of PLLA/PCL polymer blends compared to pure PLLA has been shown previously. To use numerical simulations in the design process of new components composed of the PLLA/PCL blend, a constitutive model for the material has to be established. In this work, a constitutive model for a PLLA/PCL polymer blend is established from the results of compressive tests at high and low strain rates at three different temperatures, including the body temperature. Finite element simulations of the split Hopkinson pressure bar test using the established constitutive model are carried out under the same condition as the experiments. During the experiments, the changes in the diameter and thickness of the specimens are captured by a high-speed video camera. The accuracy of the numerical model is tested by comparing the simulation results, such as the stress, strain, thickness and diameter histories of the specimens, with those measured in the experiments. The numerical model is also validated against an impact test of non-homogenous strains and strain rates. The results of this study provide a validated numerical model for a PLLA/PCL polymer blend at strain rates of up to 1800s−1 in the temperature range between 22°C and 50°C.

Tg and Tg breadth of poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene miscible polymer blends characterized by differential scanning calorimetry, ellipsometry, and fluorescence spectroscopy

The glass transition temperature (Tg) behavior of bulk, miscible poly(2,6-dimethyl-1,4-phenyleneoxide)/polystyrene (PPO/PS) blends was studied by differential scanning calorimetry (DSC), ellipsometry, and fluorescence. Previous studies have shown that two underlying component Tgs can be quantified by fluorescence in blends for which DSC fails to do so, either because the difference in homopolymers Tgs is too small or one component is at trace levels. However, all methods show only a single glass transition in PPO/PS blends, indicating that the existence of two effective Tgs due to self-concentration effects is not a universal phenomenon in miscible polymer blends with a large Tg contrast. A Tg-broadening effect is quantified in PPO/PS blends by both DSC and ellipsometry, but the glass transition breadth is relatively small, smaller even than for some homopolymers. The PPO/PS blends show a maximum Tg breadth at ∼85 wt% PPO by DSC but at ∼50 wt% PPO by ellipsometry. Thus, the details of Tg breadth for a multicomponent material can differ significantly between techniques, even when each technique evaluates Tg breadth on a basis grounded in fundamental quantities (temperature dependence of heat capacity or of thermal expansivity). While fragility is useful in understanding perturbations to Tg of well-dispersed, trace levels of one polymer by its blend partner in immiscible blends, fragility is not significantly correlated with Tg perturbations in the form of Tg breadth in strongly miscible PPO/PS blends with coupled dynamics, e.g., neat PPO has a high fragility relative to some blend compositions but a much smaller Tg breadth.

Investigation on crystallinity, performance and processability of naturally occurring halloysite nanotubes compatibilized sPS/LCP thermoplastic nanocomposites

This article deals with the analyses of the effect of halloysite nanotubes (HNTs) and modified HNTs (mH) with minimal loading on the properties of syndiotactic polystyrene (sPS)/liquid crystalline polymer (LCPs) blends. Modification of HNTs with N-(β-aminoethyl)-γ-aminopropyl-trimethoxysilane (APTMS) is confirmed by Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) studies. Intensification of crystallinity of the thermoplastic blends due to induced nucleation by the halloysite nanotubes are corroborated by XRD as well as Differential Scanning Calorimetry (DSC). Due to favorable LCP fibrillations, nanocomposites exhibited higher dynamic mechanical properties than the matrix polymer as observed from the Dynamic Mechanical Analysis (DMA). Rheological properties of the blends were upgraded whereas; the chain orientations along with their alignments were highly influenced by both unmodified and modified HNTs. Modification of HNTs brings compatibility in between the blend partners revealing improved crystallization, morphological, rheological, and thermo-mechanical properties relative to that of pure matrix.

Localization of carbon nanotubes in polyamide 6 blends with non-reactive and reactive rubber

Blending of two immiscible polymer matrices can be an effective way to combine favourable properties of both blend partners. The additional incorporation of multiwalled carbon nanotubes (MWCNTs) in such thermoplastic blends may further enhance the blend properties and especially generate electrical conductivity.In the present study, 20 wt.% of non-reactive rubber and maleic anhydride functionalized rubber were melt blended with polyamide 6 and 3 wt.% MWCNTs by using different incorporation strategies. For the blends containing non-reactive rubber, the MWCNTs were always localized selectively in the thermodynamically preferred polyamide phase as shown by TEM images and electrical measurements. Interestingly, the different strategies resulted in different localization behaviours of the MWCNTs in case of the reactive rubber. These findings demonstrate the significant influence of maleic anhydride groups of the rubber component on localization of MWCNTs in the different blend phases which results in different values of electrical volume resistivity of the blends.

Nano-/microfibrillar polymer–polymer and single polymer composites: The converting instead of adding concept

Abstract The article describes the concept of converting instead of adding used for preparation of the two new polymer materials, namely, the nano/microfibrillar polymer–polymer composites (PPCs) and the true nanofibrillar single polymer composites (SPCs). The reasons for the failure of the common polymer nanocomposites, i.e. those prepared via adding of nano-sized fillers to the polymer matrix are mentioned, followed by description of the definitions, nomenclature, advantages and disadvantages of the nanofibrillar polymer–polymer composites and SPCs. After discussing the basic problems in polymer science and technology as the environmental impact, the interfacial adhesion quality in polymer composites, and the aspect ratio of the reinforcing component, the currently most important technique for converting the polymers into nano-sized materials, the electrospinning, is critically analyzed and compared with the concept of nanofibrillar composites (NFCs). According to NFC after extrusion and cold drawing of a polymer blend, followed by selective dissolution of the major component, neat nanofibrils (with diameters of 50–250 nm) can be separated. The latter can be used for SPCs manufacturing characterized by superior mechanical properties (improvement of tensile modulus and strength up to 400%). This method for converting of any bulk polymer into nano-sized material was recently made environmental-friendly by using water only as a solvent. Its further development was the control of the final nanomorphology: (i) if H-bonding between the blend partners is missing, the observed morphology is of individual not interconnected nanofibrils and (ii) in case H-bonds are present the nanomorphology represents a nanofibrillar nanoporous 3-D network. In this way the method allows the manufacturing of nanofibrillar PPCs and SPCs avoiding the dispersion problem (for PPCs) as well as the problem of interface adhesion quality (for SPCs).

Compatibilizing effect of halloysite nanotubes in polar–nonpolar hybrid system

ABSTRACTThis article explores the effect of halloysite nanotubes (HNTs) and modified HNTs (M‐HNTs) on the properties of immiscible blend system based on polar polyoxymethylene (POM) and nonpolar polypropylene (PP) polymers. HNTs have been modified by N‐(β‐aminoethyl)‐γ‐aminopropyltrimethoxysilane (APTMS). Modification is confirmed by Fourier transform infrared spectroscopy (FTIR), also FTIR confirms the interaction between polymer blend and HNTs/M‐HNTs. Morphology of the nanocomposites are demonstrated by scanning electron microscope (SEM) and dispersion of HNTs/M‐HNTs are observed by transmission electron microscope (TEM). In nanocomposites, average dispersed domain sizes reduce in the presence of HNTs/M‐HNTs but significant reduction has been observed in the case of M‐HNT‐filled nanocomposites rather than unmodified HNT‐filled nanocomposites. The M‐HNT acts as a reinforcing agent as well as bridging tool in polar–nonpolar hybrid system. Modification of HNTs brings compatibility in between the blend partners and reveals improved dynamic mechanical, thermal, and tensile properties than that of the pure blend system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39587.

Fabrication and characterization of biodegradable polymer scaffolds adapting microfibrillar composite concept

ABSTRACTIn this work, we report on a technique for manufacturing of polymer scaffolds free from contact with toxic solvents. The method is adapted from the modified microfibrillar reinforced composites (MFC) concept. The objects of the investigation were biodegradable poly (l‐lactide) (PLLA) and biocompatible poly (ethylene‐vinyl alcohol copolymer) (EVAL). The polymers were melt blended and thereafter cold drawn, so that both of the components were converted in fibrillar state. After selective dissolving of the EVAL from the drawn bristles with mixture of propanol and water, the individual PLLA fibrils were isolated. By means of freeze‐drying, ultrafine fibrous scaffolds were obtained. All materials under investigation were characterized by X‐ray diffraction, differential scanning calorimeter, Fourier transform infrared spectrometry, scanning electron microscopy, and atomic force microscopy analysis. The experimental results provide evidence for the changes of the supra molecular organization of the blend partners during MFC manufacturing process, for the nanostructure and microstructure of the PLLA fibrils as well as for the three‐dimensional architecture of the scaffolds. The in vitro studies show that the incubated in the presence of PLLA fibrils media does not reduce the cell viability and proliferative activity of the cultured cells. This kind of multiscale scaffolds might emulate the morphology of the natural extracellular matrix and represent an appropriate material for medical application. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1298–1310

H-bonding – a chance for novel nano-sized polymers

tions in chemistry – they are about 10 times weaker than the covalent bonds between the atoms but still some 3–5 times stronger than the van der Waals forces. While the establishment of covalent or ionic bonds results in creation of new compounds differing in their chemical composition, the H-bonding is responsible for the formation and preservation of the 3-D shape of molecules, particularly in the case of macromolecules, and thus determining to a great extent the functional properties of the latter. For example, the double helical structure of DNA is due largely to H-bonding, similarly to the secondary structures of proteins. This type of bond occurs also in inorganic molecules, such as water and it is the main reason for the peculiar properties of water. Many polymers are strengthened by hydrogen bonds in their main chains. Among the synthetic polymers the best known example are polyamides, while the greatest effect observed is in aramide fibre. H-bonds are also important in the structure of cellulose and derived polymers in its many different forms in nature, such as wood and natural fibers (cotton and flax). Hydrogen bonding in polymer blends is a topic of great interest to polymer scientists because such systems have many potential applications. For example, introducing functional groups to one component to make it capable of forming hydrogen bonds to another, thereby enhancing miscibility of otherwise immiscible blends, is one of the major achievements during the past 20 years of polymer science, as stated in a recent review on hydrogen bonding in polymer blends (DOI: 10.1002/pola.22632). The H-bonding, as reported recently (DOI: 10.3144/ expresspolymlett.2011.46), represents a powerful instrument for creating a desired final nano-morphology during the conversion of bulk polymers into nano-sized materials. It was established that this morphology is of two basic types: (i) as individual not interconnected smooth nanofibrils, or (ii) as 3-D nanofibrillar nanoporous network. The first type is realized when in the starting polymer blend no H-bonding exists, and the second type – when H-bonds between the blend partners are formed. What is more, via suppressing the H-bonding in the second case it is possible to obtain the first type of nano-morphology, i.e. not interconnected individual nanofibrils.

Major Roles of Blend Partner Fragility and Dye Placement on Component Glass Transition Temperatures: Fluorescence Study of Near-Infinitely Dilute Species in Binary Blends

We measure the glass transition temperatures (Tgs) of near-infinitely dilute (0.1 wt %), well-dispersed polystyrene (PS) components in seven blend partners using intrinsic and extrinsic fluorescence. The PS Tgs span a 150 °C range when PS is dispersed in partners with Tgs of −6 to 150 °C. We calculate self-concentrations for PS (ϕselfPS) of ∼0 to 0.72 via the Lodge–McLeish model, the largest range ever reported for a blend component. Our study reveals that perturbations to PS Tg, which may be quantified by ϕselfPS calculations, correlate with partner fragility rather than partner Tg, with higher fragility partners resulting in higher ϕselfPS values. In particular, for 0.1 wt % PS in poly(vinyl chloride) (PVC), the partner with the highest reported fragility but an intermediate Tg, the PS Tg is only weakly perturbed with ϕselfPS = 0.72. These results indicate that partner fragility plays a key role in determining the strength of Tg perturbations to a blend component. Also noteworthy is 0.1 wt % PS in poly(...