Function Of Blend Composition Research Articles

Formulating PBS/PLA/PBAT blends for biodegradable, compostable packaging: The crucial roles of PBS content and reactive extrusion

The use of biodegradable polymers such as Poly (lactic acid) (PLA), Poly(butylene succinate) (PBS), and Poly(butylene adipate-co-terephthalate) (PBAT) is constantly increasing to try to substitute non-biodegradable plastics. Blending is a viable option to improve the morphology and the mechanical and heat resistance properties of biodegradable polymers. Thus, in this work, a biodegradable and compostable PLA/PBAT blend was improved by adding PBS, leading to non-reactive, melt-mixed PLA/PBAT/PBS ternary blends. The PLA/PBAT ratio was fixed at 1:1, while the PBS varied from 0 to 40 wt%. Polarized Light Optical Microscopy (PLOM) imaging showed that micro-spherulitic PBS was localized at the interface between PLA and PBAT in the blend, acting as a compatibilizer, reducing the interfacial tension and refining the ternary blend's morphology. Consequently, the mechanical properties improved, such as the elongation at break, which increased from 70 to 300 %. However, these tertiary non-reactive blends were found to lack adequate rheological properties to be processed by blown film extrusion. Therefore, reactive blending was performed by adding peroxide and carbodiimide, leading to a finer morphology and improved rheological properties. Thus, these reactive blends were successfully processed by blown film extrusion. Two types of blown films were produced, Tubular and Champagne films (DDR/BUR ratio of 37.6 and 5.2, respectively). Both types of blown films exhibited adequate ductile mechanical properties for film packaging applications, as well as high seal strength and good thermal resistance. In addition, their specific mechanical properties were a function of blend composition and the degree of biaxial orientation produced during the extrusion-blowing process.

Effects of the Blending Ratio on the Design of Keratin/Poly(butylene succinate) Nanofibers for Drug Delivery Applications.

In recent years there has been a growing interest in the use of proteins as biocompatible and environmentally friendly biomolecules for the design of wound healing and drug delivery systems. Keratin is a fascinating protein, obtainable from several keratinous biomasses such as wool, hair or nails, with intrinsic bioactive properties including stimulatory effects on wound repair and excellent carrier capability. In this work keratin/poly(butylene succinate) blend solutions with functional properties tunable by manipulating the polymer blending ratios were prepared by using 1,1,1,3,3,3-hexafluoroisopropanol as common solvent. Afterwards, these solutions doped with rhodamine B (RhB), were electrospun into blend mats and the drug release mechanism and kinetics as a function of blend composition was studied, in order to understand the potential of such membranes as drug delivery systems. The electrophoresis analysis carried out on keratin revealed that the solvent used does not degrade the protein. Moreover, all the blend solutions showed a non-Newtonian behavior, among which the Keratin/PBS 70/30 and 30/70 ones showed an amplified orientation ability of the polymer chains when subjected to a shear stress. Therefore, the resulting nanofibers showed thinner mean diameters and narrower diameter distributions compared to the Keratin/PBS 50/50 blend solution. The thermal stability and the mechanical properties of the blend electrospun mats improved by increasing the PBS content. Finally, the RhB release rate increased by increasing the keratin content of the mats and the drug diffused as drug-protein complex.

Dynamics and rheology of ring-linear blend semidilute solutions in extensional flow: Single molecule experiments

Ring polymers exhibit unique flow properties due to their closed chain topology. Despite recent progress, we have not yet achieved a full understanding of the nonequilibrium flow behavior of rings in nondilute solutions where intermolecular interactions greatly influence chain dynamics. In this work, we directly observe the dynamics of DNA rings in semidilute ring-linear polymer blends using single molecule techniques. We systematically investigate ring polymer relaxation dynamics from high extension and transient and steady-state stretching dynamics in a planar extensional flow for a series of ring-linear blends with varying ring fraction. Our results show multiple molecular subpopulations for ring relaxation in ring-linear blends, as well as large conformational fluctuations for rings in a steady extensional flow, even long after the initial transient stretching process has subsided. We further quantify the magnitude and characteristic time scales of ring conformational fluctuations as a function of blend composition. Interestingly, we find that the magnitude of ring conformational fluctuations follows a nonmonotonic response with increasing ring fraction, first increasing at low ring fraction and then substantially decreasing at large ring fraction in ring-linear blends. A unique set of ring polymer conformations are observed during the transient stretching process, which highlights the prevalence of molecular individualism and supports the notion of complex intermolecular interactions in ring-linear polymer blends. In particular, our results suggest that transient intermolecular structures form in ring-linear blends due to a combination of direct forces due to linear chains threading through open rings and indirect forces due to hydrodynamic interactions; these combined effects lead to large conformational fluctuations of rings over distributed time scales. Taken together, our results provide a new molecular understanding of ring polymer dynamics in ring-linear blends in the nonequilibrium flow.

Chitosan polyvinyl alcohol blend films for ibuprofen encapsulation: Fabrication, characterization and kinetics

Hereby, the effectiveness of ibuprofen release from chitosan/polyvinyl alcohol blend films prepared by solvent casting method was studied as a function of blend composition and cross-linking density. Genipin was used as the cross-linker. Miscibility of blend components was verified by FTIR and SEM analyses. Based on the results of ninhydrin assay, optimal genipin concentration was determined as 0.25 mM. Genipin induced inter and intramolecular hydrogen bonding aided in the enhancement of tensile strength and mechanical stability as shown with swelling tests. Concordantly, burst release was hindered and more efficient release profile was obtained for crosslinked blend. The kinetics of ibuprofen release was best described by Korsmeyer Peppas model implying that diffusion and polymer relaxation were the underlying mechanisms for either non-crosslinked or genipin cross-linked blends. Over 96% of cell viability was recorded in WST-1 assay. All these results suggested that ibuprofen encapsulated chitosan polyvinyl alcohol blends crosslinked by genipin could be used as pain suppressing wound dressing material.

PH stimuli drug loading/release platforms from LbL single/blend films: QCM-D and in-vitro studies

Here, Layer-by-Layer (LbL) films of PDADMAC and single/blend PAA/PSS were described for the drug loading/release platform. For this purpose, the effects of chemical composition of LbL film and drug type on loading/release properties were studied as a function of blend composition, pH and ionic strength of the polyelectrolytes (PEs)/releasing medium using QCM-D and UV–vis analyses. 15 % and 23 % (w/w) IBF-Na and DCF-Na loading were found without multilayer decomposition for LbL multilayers of (PDADMAC5.5/PAA5.5)10 while lower drug loadings were observed for PAA/PSS blend or single PSS containing LbL films. Drug sorption results obtained by QCM-D and UV–vis analyses were fitted very well. In-vitro studies, the loaded drugs were mostly released from the LbL films within 5 min. It was evaluated that IBF/DCF-Na release% of LbL multilayered films can be controlled as a function of pH, ionic strength, and single/blend composition as well as hydrophilicity, morphology, and topography of these films. In conclusion, these films may be good candidates as encouraging platforms for pH stimuli drug loading/release applications.

Permittivity of gasoline/methanol blends. Application to blend composition estimation

The relative permittivity of gasoline/methanol blends was determined at 100 kHz, in the full range of composition, at temperatures between 296 K and 323 K.From experimental results, permittivity is fitted to a third degree polynomial on methanol content, and, at each composition, the permittivity of blends decreases linearly with temperature.From the analysis of the experimental data, a model is developed to estimate the relative permittivity as a function of blend composition and temperature. The model fitting is very satisfactory, with an RMS absolute uncertainty of 0.43. The parameters of the model are determined from experimental data for pure gasoline and methanol, and were checked by means of a non-linear fitting using all the experimental data, with very good agreement.Another model is proposed to estimate the composition of blends from temperature and permittivity measurements. From the comparison to experimental data, the RMS absolute uncertainty of the estimation is below 2%.

Improving the barrier properties of a biodegradable polyester for packaging applications

Miscible and thermally stable blends of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) with poly(hydroxy ether of bisphenol A) (PH) are investigated to obtain membranes for packaging applications. Previously the miscibility and adequate degradability of these blends was proven, therefore this system is a good candidate for packaging applications. The crystallinity degree and the free volume, both of crucial importance in transport properties, are analysed as a function of blend composition. The transport properties to different gases and vapours are greatly reduced with the addition of PH. The blends show high elongational viscosity values, which allows expecting good film processability. Overall, this work sheds light on the factors involved in the reduction of permeability which would allow to broaden this strategy to other promising biodegradable materials.

Rheology⁻Microstructure Relationships in Melt-Processed Polylactide/Poly(vinylidene Fluoride) Blends.

In this study, small amplitude oscillatory shear tests are applied to investigate the rheological responses of polylactide/poly(vinylidene fluoride) (PLA/PVDF) blends and to correlate their viscoelastic properties with the morphological evolutions during processing. Although the analysis of the elastic moduli reveals some changes as a function of blend composition and processing time, the weighted relaxation spectra are shown to be more useful in detecting changes. The analysis demonstrates that when PVDF, i.e., the more viscous phase, is the matrix, the blend relaxes cooperatively and only a single relaxation peak is observed. By contrast, blends with highly concentrated morphologies do not fully relax, showing instead an upward increasing trend at longer times. This outcome is attributed to the broad distribution of highly concentrated droplets with a high probability of droplet–droplet contacts. Dynamic mechanical analysis (DMA) reveals that crystalline segmental motions attributed to the α-relaxation of PVDF at around 100 °C are restricted by the highly concentrated morphology of the 50/50 PLA/PVDF blend processed for 10 min. Relaxation analyses of the blends via dynamic oscillatory shear tests and DMA are shown to be powerful tools for investigating small microstructural changes in immiscible polymer blends.

Morphology and property changes in PLA/PHBV blends as function of blend composition

PLA/PHBV blends were prepared by melt mixing. The morphology and physical properties of the blends and neat polymers were investigated. Scanning electron microscopy (SEM) studies provided evidence of interfacial cavities and weak interfacial interaction between the two polymers, and no obvious co-continuous morphology was observed in any of the investigated blends. Positron annihilation lifetime spectroscopy (PALS) indicated the presence of open-volume cavities with sub-nanometre diameters; far smaller than observed from the SEM images. The mean size and relative concentration of these cavities increased with increasing PHBV content. A weak negative deviation in the mean size for low PHBV content possibly indicates some degree of partial miscibility. The glass transition temperature of PLA in the blends decreased with increasing PHBV content, and offers support to some PHBV being miscible with the PLA. The degree of crystallinity in the blends show interesting behaviour that may be explained in terms of the complex morphology observed for these blends. The thermal conductivity of the samples varied with composition, but increased with increasing PHBV content, which was probably related to the increasing crystallinity. Both the tensile strength and Young’s modulus decreased with increasing PHBV content for the sequence of blends, and both parameters exhibited maximum values for 10 wt.% PHBV. For samples between 50/50 and 10/90 PLA/PHBV the tensile strength and Young’s modulus were comparable to or lower than those for both the neat polymers.

Phase separation in amorphous hydrophobically modified starch–sucrose blends: Glass transition, matrix dynamics and phase behavior

The phase behavior and matrix dynamics of amorphous blends of octenyl succinic anhydride (OSA) modified starch and sucrose was studied as function of blend composition and water content. Phase separation into two amorphous phases, one enriched in OSA starch and the other in sucrose, was confirmed by differential scanning calorimetry (DSC). DSC and 1H solid-state NMR show that the phase separation is only partial. The glass transition temperature (Tg) of the OSA starch-rich phase was found to be ∼30–100 K higher than the Tg of the sucrose-rich phase, depending on blend composition and water content. A novel type of coupling between changes in physical state of the sucrose-rich phase and plasticizer redistribution is proposed, leading to an unexpected increase of the glass transition temperature of the modified starch-rich phase at higher matrix water contents. A quantitative model for the phase separation of the anhydrous blends into two amorphous phases is presented. The model predicts that, with increasing blend sucrose content, the weight fraction of the sucrose-rich phase decreases, while the sucrose content of both the OSA starch-rich phase and the sucrose-rich phase increases. This novel phenomenon is relevant in the understanding of the stability and performance of multiphase food and pharmaceutical components.

Study on the Miscibility of Polypyrrole and Polyaniline Polymer Blends

We report on the miscibility and phase behaviour of polypyrrole‐polyaniline (PPy/PANI) as a function of blend composition. The PPy/PANI blends were prepared by solution processing method, using dimethyl sulfoxide (DMSO) solvent. Characterization of the polymer blends was carried out based on the data analysis from Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), and differential scanning calorimetry (DSC). The PPy/PANI system was successfully formed blends in DMSO solvent. The polymer blends showed almost amorphous nature in XRD spectra because of intermolecular interaction between PPy and PANI macromolecules, which was confirmed by FT‐IR data. Specifically, the DSC result for the PPY : PANI = 50 : 50 wt.% blend showed only one glass transition temperature (Tg), which indicates that the two polymers are well miscible without undergoing any phase separation.

Charge Separation in Intermixed Polymer:PC70BM Photovoltaic Blends: Correlating Structural and Photophysical Length Scales as a Function of Blend Composition

A key challenge in achieving control over photocurrent generation by bulk-heterojunction organic solar cells is understanding how the morphology of the active layer impacts charge separation and in particular the separation dynamics within molecularly intermixed donor–acceptor domains versus the dynamics between phase-segregated domains. This paper addresses this issue by studying blends and devices of the amorphous silicon–indacenodithiophene polymer SiIDT-DTBT and the acceptor PC70BM. By changing the blend composition, we modulate the size and density of the pure and intermixed domains on the nanometer length scale. Laser spectroscopic studies show that these changes in morphology correlate quantitatively with the changes in charge separation dynamics on the nanosecond time scale and with device photocurrent densities. At low fullerene compositions, where only a single, molecularly intermixed polymer–fullerene phase is observed, photoexcitation results in a ∼ 30% charge loss from geminate polaron pair r...

Curing behaviors of cyanate ester/epoxy copolymers and their dielectric properties

The curing behavior and dielectric properties of cyanate ester/epoxy (EP) with a latent initiator imidazole was investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic cure behavior of the blends. Multiheating rate DSC, peak fitting, and iso-conversion method were applied to analyze the curing kinetic parameters. Two distinct peaks were fitted from the dynamic DSC curve and the activation energies of each reaction varied with the increase of curing degrees. Fourier transform infrared spectra revealed that several reactions coexisted during the curing processes of cyanate and EP, resulting in the coexistence of the polymers and copolymers in the final composites. The dielectric properties of the composites were studied and the phenomenon that the dielectric constants for all of the composites are independent of frequency was observed. The thermal decomposition characteristics of the blends were investigated using thermogravimetric analysis. By increasing the content of EP, the thermal properties of the cured blends were improved to a small extent, while the char yield markedly decreased.

How the Energetic Landscape in the Mixed Phase of Organic Bulk Heterojunction Solar Cells Evolves with Fullerene Content

Energy levels in the mixed polymer:fullerene phase of three-phase bulk heterojunction solar cells are significantly shifted from their values in the pure materials. These shifts provide an important driving force for separating charge carriers. Through cyclic voltammetry, we measure a gradual shift in the polymer HOMO and fullerene LUMO as a function of blend composition in a model bulk heterojunction (BHJ) system that only contains amorphous polymer. The effective band gap of the polymer:fullerene blend varies by up to 300 meV with varying blend composition. The shifts in polymer HOMO and fullerene LUMO can be quantitatively accounted for by the electrostatic potential generated by induced dipoles at the polymer:fullerene interfaces. Remarkably, however, the measured charge transfer state energy and open-circuit voltage shift far less.

Effect of blend ratio on the dynamic mechanical and thermal degradation behavior of polymer–polymer composites from low density polyethylene and polyethylene terephthalate

Microfibrillar polymer–polymer composites (MFCs) based on low-density polyethylene (LDPE) and polyethylene terephthalate (PET) were prepared by cold drawing-isotropization technique. The weight percentage of PET was varied from 5 to 45 %. Microfibrils with uniform diameter distribution were obtained at 15 to 25 wt% of PET as evident from the scanning electron microscopy (SEM) results. Dynamic mechanical properties such as storage modulus (E′), loss modulus (E″) damping behavior (tan δ) were examined as a function of blend composition. The E′ values were found to be increasing up to 25 wt% of PET. An effort was made to model the storage modulus and damping characteristics of the MFCs using the classical equations used for short-fiber reinforced composites. The presence of PET microfibrils influenced the damping characteristics of the composite. The peak height at the β-transitions of loss modulus was lower for MFCs with 25 % PET, showing that they had superior damping characteristics. This phenomenon could be correlated with the PET microfibrils morphology. The thermal degradation characteristics of LDPE, neat blends and microfibrillar blends (MFBs) were compared. The determination of activation energy for thermal degradation was carried out using the Horowitz and Metzger method. The activation energy for thermal degradation of microfibrillar blends was found to be higher than that for the corresponding neat blends and MFCs. The long PET microfibrils present in MFBs could prevent the degradation and enhance the activation energy.

Amorphous-amorphous phase separation in hydrophobically-modified starch–sucrose blends II. Crystallinity and local free volume investigation using wide-angle X-ray scattering and positron annihilation lifetime spectroscopy

Positron Annihilation Lifetime Spectroscopy (PALS) has been employed to characterize the temperature dependence of the local free volume of hydrophobically-modified starch (HMS) – sucrose (S) blends as a function of blend composition and water content. The findings from PALS support the conclusions drawn from thermodynamic characterization using Differential Scanning Calorimetry (DSC) showing evidence of limited phase separation between the HMS and S phases, inferred from the drastic change in the temperature dependence of the average size of the local free volume element as a function of blend composition. The effect of water content on the average local free volume element size is in good agreement with previous studies on simpler carbohydrate polymer/low molecular weight inclusion blends, however, the width of the free volume distribution is also observed to be affected by water content. This is interpreted to be related to the heterogeneity of the free volume holes, which is higher for phase-separated systems comprising phases of different composition and molecular weight distribution. Wide angle X-ray scattering (WAXS) was employed to study the crystallinity of the blends, showing limited crystallinity is present in the blends at the highest water contents with origin in the corn starch (CS) added during processing, and not the HMS and S phases.

Amorphous–amorphous phase separation in hydrophobically-modified starch–sucrose blends I. Phase behavior and thermodynamic characterization

The glass transition of amorphous powders consisting of blends of octenyl-succinic anhydride (OSA) modified starch, and sucrose was studied as a function of blend composition and water content. Polarized light microscopy, differential scanning calorimetry (DSC) and water vapor sorption analysis were performed on four blends varying in their modified starch to sucrose ratio. The thermograms of the blends exhibit either a single glass transition event, characterized by a quite broad temperature range, or two glass transitions. This hints at a limited degree of phase separation into two amorphous phases within the blend matrix, most likely at the microscale. The results from dynamic water vapor sorption studies indicate that, in the phase-separated blends, the sucrose-rich phase constitutes the dispersed phase, while the continuous phase is formed by the phase rich in OSA starch. Our findings open up new ways to engineer glass encapsulation systems with composite structure, which can provide for a high level of protection of encapsulated bioactive compounds as well as defined release properties.

Processing and characterization of bio‐based poly (hydroxyalkanoate)/poly(amide) blends: Improved flexibility and impact resistance of PHA‐based plastics

ABSTRACTOne of the most significant limitations to widespread industrial implementation of emerging bioplastics such as poly(lactic acid) and poly(hydroxyalkanoate) (PHA) is that they do not match the flexibility and impact resistance of petroleum‐based plastics like poly(propylene) or high‐density poly(ethylene). The basic goal of this research is to identify alternative, affordable, sustainable, biodegradable materials that can replace petroleum‐based polymers in a wide range of industrial applications, with an emphasis on providing a solution for increasing the flexibility of PHA to a level that makes it a superior material for bioplastic nursery‐crop containers. A series of bio‐based PHA/poly(amide) (PA) blends with different concentrations were mechanically melt processed using a twin‐screw extruder and evaluated for physical characteristics. The effects of blending on viscoelastic properties were investigated using small‐amplitude oscillatory shear flow experiments to model the physical character as a function of blend composition and angular frequency. The mechanical, thermal, and morphological properties of the blends were investigated using dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and tensile tests. The complex viscosity of the blends increased significantly with increasing concentration of PHA and reached a maximum value for 80 wt % PHA blend. In addition, the tensile strength of the blends increased markedly as the content of PHA increased. For blends containing PA at >50 wt %, samples failed only after a very large elongation (up to 465%) without significant decrease in tensile strength. The particle size significantly increased and the blends became more brittle with increasing concentration of PHA. In addition, the concentration of the PA had a substantial effect on the glass relaxation temperature of the resulting blends. Our results demonstrate that the thermomechanical and rheological properties of PHA/PA blends can be tailored for specific applications, and that blends of PHA/PA can fulfill the mechanical properties required for flexible, impact‐resistant bio‐based nursery‐crop containers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42209.

Enhanced mobility and effective control of threshold voltage in P3HT-based field-effect transistors via inclusion of oligothiophenes.

Improved organic field-effect transistor (OFET) performance through a polymer-oligomer semiconductor blend approach is demonstrated. Incorporation of 2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene (BTTT) into poly(3-hexylthiophene) (P3HT) thin films leads to approximately a 5-fold increase in charge carrier mobility, a 10-fold increase in current on-off ratio, and concomitantly, a decreased threshold voltage to as low as 1.7 V in comparison to single component thin films. The blend approach required no pre- and/or post treatments, and processing was conducted under ambient conditions. The correlation of crystallinity, surface morphology and photophysical properties of the blend thin films was systematically investigated via X-ray diffraction, atomic force microscopy and optical absorption measurements respectively, as a function of blend composition. The dependence of thin-film morphology on the blend composition is illustrated for the P3HT:BTTT system. The blend approach provides an alternative avenue to combine the advantageous properties of conjugated polymers and oligomers for optimized semiconductor performance.

Solution Self-Assembly of Blends of Crystalline-Coil Polyferrocenylsilane-block-polyisoprene with Crystallizable Polyferrocenylsilane Homopolymer

The self-assembly of block copolymers in solution leads to micellar structures with various morphologies. One way to modify the morphology of these micelles is to blend the block copolymer with a homopolymer corresponding to the core-forming block. Although the self-assembly of blends of amorphous homopolymers and block polymers has been extensively studied, there are few examples of solution self-assembly of blends of a core-crystalline block copolymer with a semicrystalline homopolymer. Here we describe a systematic study of the assembly in decane of blends of a polyferrocenylsilane-block-polyisoprene sample (PFS48-b-PI264) with two different PFS homopolymer samples (PFS50 and PFS20). We examine the structures formed as a function of blend composition and compare them to the structures formed from the individual components. PFS48-b-PI264 itself forms long cylindrical micelles, while the two homopolymer samples form stacks of lamellar crystals. Self-assembly of block copolymer mixtures leads to structures with an elongated planar core and fiber-like protrusions from the ends. The details of the structure vary in an interesting and systematic way as the ratio of homopolymer/block copolymer is increased, with important differences seen for the PFS50 and PFS20 homopolymer samples. This study demonstrates that cocrystallization plays a crucial role in determining the structures formed from these mixtures.