Morphology Of Blends Research Articles

Air-Knife-Assisted Spray Coating of Organic Solar Cells.

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have risen dramatically since the introduction of the "Y-series" of non-fullerene acceptors. However, the demonstration of rapid scalable deposition techniques to deposit such systems is rare. Here, for the first time, we demonstrate the deposition of a Y-series-based system using ultrasonic spray coating─a technique with the potential for significantly faster deposition speeds than most traditional meniscus-based methods. Through the use of an air-knife to rapidly remove the casting solvent, we can overcome film reticulation, allowing the drying dynamics to be controlled without the use of solvent additives, heating the substrate, or heating the casting solution. The air-knife also facilitates the use of a non-halogenated, low-toxicity solvent, resulting in industrially relevant, spray-coated PM6:DTY6 devices with PCEs of up to 14.1%. We also highlight the obstacles for scalable coating of Y-series-based solar cells, in particular the influence of slower drying times on blend morphology and crystallinity. This work demonstrates the compatibility of ultrasonic spray coating, and use of an air-knife, with high-speed, roll-to-roll OSC manufacturing techniques.

Toward understanding the crystallization behavior of polypropylene‐based nanocomposites: Effect of ethylene–octene copolymer and nanoclay localization

AbstractThe crystallization properties of polypropylene (PP), a widely used polymer in industry, can be modified to overcome its mechanical limitations. In the current work, we investigated the effect of ethylene octene copolymer (EOC), blend morphology, nanoclay loading, nano‐localization, and component ratios on PP/EOC crystallization behavior in various aspects, including crystallization rate, degree of crystallinity, nucleation state, and crystalline phases. The results revealed that adding EOC with varying ratios can decrease PP crystallinity both in degree and rate due to the partial miscibility of components through grafting. Furthermore, it was found that the effect of the nanoclay on the crystallization behavior of PP is dependent on the nanoclay loading and its localization in the blend. The nanoclay, therefore, served as a nucleation agent at low nanoparticle contents, accelerating the crystallization rate regardless of the blend's microstructure. However, the crystallization rate of the blend samples at high nanoclay contents (above the rheological percolation threshold) was strongly influenced by the type of morphology. Accordingly, high nanoclay concentrations in blends with matrix‐dispersed morphologies reduced crystallization rates (increasing half‐time from 164 to 216 and 186 s), primarily because PP chains slowed down due to their interactions with nanoparticles and nanoclay hindrance. In contrast, in a blend with a co‐continues‐type morphology, the crystallization rates increased (decreasing half‐time from 624 to 270 and 236 s) due to nano‐localization at the interface and morphology transformation to the matrix‐dispersed one. The blends and nanocomposites based on PP/EOC were also investigated to determine the relationship between the crystallization behavior and mechanical properties.

Polythiophene-based terpolymers with modulated aggregation behaviors for high-performance organic solar cells with 16.6% efficiency

Polythiophenes (PTs) are an attractive class of polymer donors (PDs) for organic solar cells (OSCs) owing to their relatively simple structures and scalable synthesis. Herein, a series of chlorinated thiazole-incorporated PT terpolymers are designed and high-performance OSCs with a power conversion efficiency (PCE) of 16.6% are demonstrated. By incorporating two different units, 3,3′-difluoro-2,2′-bithiophene (T2F2) and thieno[3,2-b]thiophene (TT), the aggregation properties of the terpolymers (PTz-FX; X = 0, 30, 50, 70, and 100, where X represents the mole percentage of T2F2 to total T2F2 +TT) are modulated. Among the PTz-FX series, PTz-F70 is found to be the optimal PD because its suitably tuned aggregation property leads to an optimized blend morphology with well-developed crystalline structures and donor–acceptor intermixed domains. The balanced morphology not only promotes charge generation/transport but also suppresses charge recombination in OSC devices. Thus, the PTz-F70-based OSCs achieve the highest PCE (16.6%), outperforming the OSCs based on PTz-FX with extremely strong (PTz-F100, PCE = 14.7%) or weak (PTz-F0, PCE = 12.0%) aggregation properties. The PCE of the PTz-F70-based OSCs is one of the highest performances among PT-based binary OSCs. This study highlights the importance of controlling the aggregation property of PTs for achieving high-performance PT-based OSCs.

Particle-size dependent stability of co-continuous polymer blends

The properties of polymer blend nanocomposites are typically associated with spatiotemporal distribution of nanoparticles within a polymer blend system. Here, we present in situ high-temperature confocal rheology studies to assess the effect of particle size on the extent of particle agglomeration, particle migration, and subsequently their influence on the coarsening dynamics of polymer blends filled with pristine silica particles. We investigate co-continuous polypropylene-poly(ethylene-co-vinyl acetate) blends filled with five different silica particles with a diameter ranging from 5 to 490 nm. While particle size does not play a role when particles are thermodynamically driven to their preferred polymer phase, a striking effect is achieved when particles are kinetically trapped at the interface. We find that the interparticle interaction largely driven by size dependent long-range repulsive forces governs their extent of agglomeration, severely affecting their ability to stabilize co-continuous morphology. Strikingly, the largest (490 nm) particles are more effective in suppressing coarsening than 5 nm particles, while 140 and 250 nm particles are found to be the most effective. We demonstrate that kinetic trapping of primary particles of either size is influenced by the interplay of interfacial folding during melt blending and Laplacian pressure exerted at the interface. These results extend our fundamental understanding of the stabilization of co-continuous morphology in polymer blends by particles.

Tris-homoleptic cyclometalated Ir(III) complexes based on oligothiophene-derived ligands as electron donors for organic solar cells

Herein, two octahedral homoleptic tris-Ir(III) complexes namely Py3T3Ir and Py5T3Ir are designed from pyridine/oligothiophene hybridized cyclometalated ligands with different conjugation lengths. Py5T3Ir with enlarged conjugation shows bathochromic absorption, strengthened absorptivity in longer-wavelength region and lower-lying energy levels compared to Py3T3Ir. Moreover, Py3T3Ir bearing small-sized backbones presents stronger triplet characteristic with boosted phosphorescence and prolonged exciton lifetimes. Blending ZY-4Cl acceptor to construct all-small-molecule organic solar cells, Py5T3Ir performs evidently increased power conversion efficiency of 8.62% than 3.04% of Py3T3Ir. The pronounced improvement in photovoltaic performance is originated from the advantageous carrier dynamics and superior blend morphology. Our results indicate coordinated Ir complexes are expected as potential photovoltaic materials by judicious molecular design.

From Solution to Thin Film: Molecular Assembly of π-Conjugated Systems and Impact on (Opto)electronic Properties.

The assembly of conjugated organic molecules from solution to solid-state plays a critical role in determining the thin film morphology and optoelectronic properties of solution-processed organic electronics and photovoltaics. During evaporative solution processing, π-conjugated systems can assemble via various forms of intermolecular interactions, forming distinct aggregate structures that can drastically tune the charge transport landscape in the solid-state. In blend systems composed of donor polymer and acceptor molecules, assembly of neat materials couples with phase separation and crystallization processes, leading to complex phase transition pathways which govern the blend film morphology. In this review, we provide an in-depth review of molecular assembly processes in neat conjugated polymers and nonfullerene small molecule acceptors and discuss their impact on the thin film morphology and optoelectronic properties. We then shift our focus to blend systems relevant to organic solar cells and discuss the fundamentals of phase transition and highlight how the assembly of neat materials and processing conditions can affect blend morphology and device performance.

Relationship Between The Co-Continuous Morphology of Immiscible Polymer Blends and the Structure of An In Situ Formed Graft Copolymer.

Suitable compatibilizers are essential to prepare immiscible polymer blends with stable co-continuous morphologies. From the thermodynamic point of view, such compatibilizer should not only reduce the interfacial tension, but also promote the formation of flat interface between different phases. Meanwhile, it must not hinder the coalescence of dispersed phase. Therefore, asymmetric structures are required for those block or graft copolymer compatibilizers. However, from the kinetic point of view, copolymers with asymmetric structures are prone to be dragged out from the interface and form micelles in one phase under the processing conditions, which will lose their compatibilization effects. The balance between such thermodynamic and kinetic factors remains unclear. In this paper, the relationship between the morphology of the compatibilized polystyrene/nylon 6/styrene-maleic anhydride copolymers (PS/PA6/SMA) immiscible polymer blends and the structures of the in-situ formed SMA-g-PA6 graft copolymers as well as the processing conditions are studied. Two kinds of SMA are used as compatibilizers: SMA28 (Mw = 110,000g/mol, MAH content 28wt.%) and SMA11 (Mw = 110,000g/mol, MAH content 11wt.%). After melt blending with PA6 into an internal mixer, the in-situ formed copolymer SMA28-g-PA6 has an average four PA6 side chains grafted on one SMA backbone, while that of SMA11-g-PA6 has only one PA6 side chain. Dissipative particle dynamics (DPD) simulation results indicate that both SMA28-g-PA6 copolymer and PS/PA6/SMA28 blends tend to form co-continuous structure, while SMA11-g-PA6 copolymer and PS/PA6/SMA11 blends form sea-island morphologies. However, these results are confirmed experimentally only at relatively low rotor speed of the internal mixer (60rpm). When the rotor speed of the mixer is higher (105rpm), sea-island morphologies are obtained in PS/PA6/SMA28 blends and co-continuous ones are found in PS/PA6/SMA11 systems. These results indicate that higher shear stress will favor to elongate the minor phase domains and form flat interfaces, which is benefit for the formation of co-continuous morphologies; meanwhile, high shear stress may pull the graft copolymers with asymmetric structures (SMA28-g-PA6) out from the interface of PS and PA6 and induce the formation of sea island morphologies. This article is protected by copyright. All rights reserved.

Asymmetric Polymer Additive for Morphological Regulation and Thermally Stable Organic Solar Cells.

High thermal stability is crucial for the commercialization of organic solar cells (OSCs). The thermal stability of OSCs has been improved using the tailoring blend morphology of bulk heterojunctions (BHJs). Herein, we demonstrated thermally stable OSCs in a ternary blended system containing low-crystalline semiconducting polymers (asy-PNDI1FTVT and PTB7-Th) and a non-fullerene acceptor (Y6). The asymmetric n-type semiconducting polymer (asy-PNDI1FTVT) differed from general symmetric semiconducting polymers as it randomly substituted fluorine atoms at the donor moiety (TVT), resulting in significantly lower crystallinity. asy-PNDI1FTVT in PTB7-Th:Y6 exhibited a well-mixed morphology at the BHJ and efficiently facilitated the charge dissociation process with an enhanced fill factor and power conversion efficiency. Furthermore, the ternary system of PTB7-Th:Y6:asy-PNDI1FTVT suppressed phase separation with negligible burn-in loss and performance degradation under thermal stress. The experiments showed that our devices without encapsulation retained over 90% of their initial efficiencies after 100 h at 65 °C. These results show significant potential for the development of thermally stable OSCs with reasonable efficiency.

Mutual influence of the morphology and growth kinetics in binary crystalline blends of poly(butylene terephthalate) and polyarylate

The spherulitic morphology and crystallization behaviors of binary crystalline blends of poly(butylene terephthalate) (PBT) and polyarylate (PAr), based on bisphenol A, (27:73 isophthalic:terephthalic acids), are investigated herein. PBT and PAr crystallize simultaneously or sequentially; various crystallization behaviors and morphologies are observed. In the PBT-rich blends, PAr does not crystallize; the PBT spherulites coarsen as the PAr concentration increases. Non-crystallizable PAr is trapped inside the spherulites. The PBT spherulitic growth rate decreases when PAr is added and remains constant thereafter. For the 50/50 blends, PBT and PAr crystallize simultaneously, and their spherulites co-exist separately. The spherulitic growth rate of PBT increases with time while PAr is crystallizing, but it remains constant if PAr crystallizes prior. At a crystallization temperature of 250 °C, only PAr crystallizes; the non-crystallizable PBT is expelled from the PAr spherulites because the crystallization rate of PAr is low. The spherulites of PAr do not fill the space in the final crystallization stage. The crystallization rate of the binary crystalline PBT/PAr blends was notably influenced by the prior crystallization of the other component, and was due to the change of the amorphous composition in addition to the constraints of the crystals on the chain mobility.

Miscibility Regulation and Thermal Annealing Induced Hierarchical Morphology Enables High‐Efficiency All‐Small‐Molecule Organic Solar Cells Over 17%

AbstractAchieving an ideal morphology to realize efficient charge generation and transport is an imperative avenue to improve the photovoltaic performance of all small‐molecule organic solar cells (SM‐OSCs). Here, ternary SM‐OSCs are fabricated based on a new small molecule donor, SM‐mB, and an alloyed blend acceptor of Y6 and its derivative, L8‐BO, and desirable hierarchical morphology with appropriate nanoscale phase separation is successfully realized through adjusting the thermal annealing treatment conditions and compositions of mixed acceptors in the active layer. Then the ternary SM‐OSCs achieve an excellent PCE of 17.06 %, which is one of the best results for the SM‐OSCs so far. The desirable morphology can be ascribed to the optimization of the miscibility‐driven donor and acceptor blend morphology that takes full advantage of the individual advantages of both acceptors, which facilitate efficient charge generation and extraction with more balanced charge carrier mobilities. More importantly, the photovoltaic performance of the ternary SM‐OSCs possesses a high tolerance to the device fabrication conditions, including thermal annealing treatment, and is insensitive to film thickness, which is beneficial for large‐area manufacture and future practical applications.

Influence of PMMA brushes grafted from GO on rheological properties of PMMA/SAN immiscible blend in shear and elongation flow

In real technological processes, both shear and elongational flow is present. The material properties may differ significantly under both types of flow. Hence, they both define the final morphology and thus properties of the materials. In this work, the morphology of immiscible blends containing polymer hybrid particles was related to extensional rheological properties for the first time. The effect of various lengths of polymer brushes grafted from graphene oxide particles (GO) surface was investigated. As a polymer matrix the immiscible blend of poly(methyl methacrylate)/styrene-co-acrylonitrile (PMMA/SAN) was used. Thus the poly(methyl methacrylate) (PMMA) brushes grafted from GO (GO-g-PMMA) with various number average molar masses (Mn) of PMMA brushes with respect to chain entanglement limit of freely dispersed PMMA were prepared. The extensional rheological properties were affected by Mn of PMMA brushes, while the rheological properties in shear were unchanged. Transmission electron microscopy revealed the compatibilization effect for short densely grafted brushes with Mn of 10,300 g/mol, as smaller domains were observed. On the contrary, the higher Mn PMMA brushes facilitated coalescence. With increasing length of brushes, the elongational viscosity at low elongation rates (∼< 0.1 s−1) decreased, which facilitated the coalescence. The increase of viscosity at higher elongation rates (∼> 0.1 s−1) was not sufficient enough to cause fiber breakup and thus elongated domains were formed.

18% efficiency of ternary organic solar cells enabled by integrating a fused perylene diimide guest acceptor

Constructing ternary organic solar cells (OSCs) has been the widely used and effective strategy to further enhance photovoltaic performance. Here, a novel perylene diimide (PDI) derivative, FPDI-2PDI, was developed by attaching two PDI chromophores to the bay-position of fused PDI dimer. The wide bandgap FPDI-2PDI was used as a guest electron acceptor in the classic PM6:Y6 system. The top-performing ternary device achieved simultaneously increased open-circuit voltage (Voc) of 0.848 V, short-circuit current density (Jsc) of 27.47 mA cm-2 and fill factor (FF) of 77.20%, yielding a significantly improved power conversion efficiency (PCE) of 18.00%, which is much higher than PCE of 16.63% of the control PM6:Y6 binary device. The incorporation of FPDI-2PDI is conducive to improving solar energy utilization, suppressing charge recombination, facilitating exciton dissociation and charge collection while enhancing the blend morphology, thus leading to increased photovoltaic performance in the corresponding ternary device. This work indicates that proper molecular design will make the PDI derivatives to be very competitive guest acceptors to construct high-efficiency ternary OSCs.

Highly Stretchable Printed Poly(vinylidene fluoride) Sensors through the Formation of a Continuous Elastomer Phase

Stretchable piezoelectric stress/strain sensing materials have attracted substantial research interest in the fields of wearable health monitoring, motion capturing, and soft robotics. These sensors require operation under dynamic loading conditions with high strain range, changing strain/loading rates, and varying pre-stretch states, which are challenging conditions for existing sensors to produce reliable measurements. To overcome these challenges, an intrinsically stretchable poly(vinylidene fluoride) (PVDF) sensor is developed through the polymer blending of PVDF and acrylonitrile butadiene rubber (NBR). Through precipitation printing and vulcanization, the resulting PVDF/NBR blends exhibit strong β phase PVDF and a blend morphology with submicron-level phase separation, but also strains up to 544%. Both the blend morphology and the mechanical properties indicate that this PVDF/NBR blend can be considered as a continuous elastomer phase above micron scale. After electric poling and adding electrodes, the PVDF/NBR blends have excellent piezoelectric properties to be used as both stretching mode strain sensors and compression mode stress/force sensors. The stretching mode sensors can measure strain up to 70% without strain rate and pre-stretch dependence, while the compression mode sensors have a loading-rate-independent linear voltage-stress relationship up to 4.8 MPa stress and a negligible pre-stretch dependence. Therefore, the PVDF/NBR sensors can provide accurate and reliable stress/strain measurements when attached to soft structures, which paves the way for sensing and calibration of soft robots under dynamic loading conditions.

Highly ductile, stable, and efficient organic photovoltaic blends enabled by polymerized ladder-type heteroheptacene-based small-molecule acceptors

Although many fully-conjugated polymerized small-molecule acceptors (PSMAs) with high photovoltaic performance have been reported recently, most of them exhibit high stiffness and are very brittle, which limits their applications in wearable and stretchable electronics. In this work, we show that PSMAs using ladder-type heteroheptacene-cored SMAs (M-series acceptors) as the main building blocks can achieve high mechanical ductility while maintaining high power conversion efficiencies (PCEs). To finely tune molecular stacking and miscibility of the resulting PSMAs (PQ-HD and PQ-OD), two pendant groups with different alkyl lengths (namely, 2-hexyldecyl and 2-octyldodecyl) are anchored on their backbones. With the shorter side-chains, a more intermixed bulk-heterojunction blend morphology as well as highly well-ordered molecular packing are achieved, leading to simultaneous enhancement of both photovoltaic and mechanical properties. The best-performing PSC based on PQ-HD with 2-hexyldecyl side-chains shows a high PCE of 13.36% and excellent mechanical stretchability with a crack-onset strain (COS) of 17.5%, both of which are superior to that based on PQ-OD with 2-octyldodecyl side-chains (PCE = 10.87% and COS = 12.8%). Moreover, the PQ-HD-based PSC also exhibits excellent thermal stability. These outstanding properties in combination with its low synthetic complexity shall make PQ-HD a promising candidate for future applications in flexible and wearable devices.

Rheological Characteristics of Starch-Based Biodegradable Blends.

Thermoplastic starch was blended with commercially available biodegradable polyesters of poly(butylene adipate-co-terephthalate) (PBAT) and poly(lactic acid) (PLA) for its improved performance and processability. The morphology and elemental composition of these biodegradable polymer blends were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively, while their thermal properties were analyzed using thermogravimetric analysis and differential thermal calorimetry. For rheological analysis, the steady shear and dynamic oscillation tests of three samples at various temperatures were investigated using a rotational rheometer. All three samples exhibited significant shear thinning at all measured temperatures, and their shear viscosity behavior was plotted using the Carreau model. The frequency sweep tests showed that the thermoplastic starch sample exhibited a solid state at all temperatures tested, whereas both starch/PBAT and starch/PBAT/PLA blend samples exhibited viscoelastic liquid behavior after the melting temperature such that their loss modulus at low frequencies was greater than the storage modulus, and inversion occurred at high frequencies (storage modulus > loss modulus).

Configuration-dependent photovoltaic properties of diketopyrrolopyrrole (DPP) based Ir complexes for organic solar cells

Organometallic complexes with diverse spatial configurations have been rarely investigated in organic solar cells (OSCs). In this work, two octahedral cyclometalated Ir(III) complexes of bis-heteroleptic DPPTBzIr and tris-homoleptic DPPTBz3Ir are designed from a highly planar diketopyrrolopyrrole (DPP)-containing ligand DPPTBz. Upon coordination, gradually increased optical absorption was observed with the maximum molar extinction coefficient (ε) of 3.80×104, 5.19×104 and 1.39×105 M-1 cm-1 for DPPTBz, DPPTBzIr and DPPTBz3Ir, respectively. Unexpectedly, owing to the large π-conjugation and strong intraligand donor-acceptor interactions from the cyclometalated DPPTBz ligand, no obvious triplet character is determined for the DPP-containing Ir complexes from both experimental and theoretical methods. When employed as electron donor materials for OSCs by blending with fused-ring electron acceptor N3, substantially improved power conversion efficiency (PCE) with average values from 0.74%, 2.2% to 3.41% are achieved for DPPTBz, DPPTBzIr and DPPTBz3Ir, respectively. The best photovoltaic performance for DPPTBz3Ir is originated from strengthened light harvest, suitable energy levels, manipulated blend morphologies and favorable carrier dynamics in the corresponding devices.

Employing impedance spectroscopy to investigate electrical conduction mechanism in polymer composite blends containing conductive masterbatch: PP/EVA/ (PP-g-MA/MWCNTS)

Impedance spectroscopy analysis has been employed to investigate the effect of melt mixing time on electrical conduction mechanism, direct contact or electron tunneling, of a polymer blend using a conductive masterbatch. A novel approach is proposed to correlate the dispersion/distribution states of conductive nanoparticles within the phases, achieved through kinetic control of the conductive masterbatch, and their impedance properties. A blend of polypropylene and ethylene-vinyl acetate copolymer (PP/EVA) was considered as a case study for the matrix. An electrically conductive masterbatch of multiwalled carbon nanotubes (MWCNTs) in polypropylene-grafted-maleic anhydride (PP-g-MA) was added to the blend. The masterbatch in varying amounts was mixed with PP/EVA in a range of 1 min–4.5 min. The co-continuous morphology of the ternary polymer blend was validated via scanning electron microscopy micrographs. The atomic force microscopy (AFM) results showed that as the mixing time of the masterbatch increases the interconnected structures within the conductive interphase decrease. Impedance spectroscopy using alternating current was employed to probe the conduction mechanism in the composite blends. The impedance spectroscopy results revealed that for samples with low mixing time, a dielectric relaxation peak occurs at high frequencies due to the existence of more conductive pathways as a consequence of the interconnected structures of the masterbatch phase. Also, the major contribution of conductance was direct contact in the samples with low mixing times while electron tunneling mechanism was considerable for the samples with high mixing times. Dielectric constant was increased as a result of interfacial polarization boosting with mixing time. The percolation threshold was considerably decreased from 0.95 v% for simultaneous direct mixing method to 0.16 v% for the masterbatch method.

Layer‐by‐Layer‐Processed Ternary All‐Polymer Organic Solar Cells with 17.74% Efficiency Enabled by Introducing a Designed Narrow‐Bandgap Guest Polymer Acceptor

Obtaining an admirably modified vertical phase separation of the active layer for all‐polymer solar cells (all‐PSCs) to facilitate charge generation, charge transfer and transport properties are a prerequisite for achieving high performance. Herein, the active layer of all‐PSCs is finely manipulated by combining a ternary blend strategy with a layer‐by‐layer (LbL) process. Based on the LbL‐processed PM6/PYT‐1S1Se host binary all‐PSCs, a chlorinated polymer acceptor PYT‐1S1Se‐4Cl is designed and introduced into the host system for rationally controlling blend morphology with ordered molecular stacking and suitable vertical distribution. The optimized bulk microstructure of the ternary system is not only beneficial to the charge generation and charge transport properties, but also can significantly reduce the nonradiative energy loss that occurs in the LbL‐type ternary blend. Thus, the LbL‐type PM6/(PYT‐1S1Se:PYT‐1S1Se‐4Cl) ternary all‐PSCs exhibit a promising power conversion efficiency (PCE) of 17.74%, which is higher than the corresponding binary systems (PCE = 16.86% for PM6/PYT‐1S1Se and PCE = 15.83% for PM6/PYT‐1S1Se‐4Cl), indicating the special merits of material design and processing technology. Overall, a promising combinatorial method for the morphological regulation of all‐polymer systems is demonstrated that contributes to enhanced efficiency.

Effect of LNR-g-MMA on the Mechanical Properties and Lifetime Estimation of PLA/PP Blends.

Polylactide (PLA) polymer, polypropylene (PP) polymer, and a PLA/PP (70:30 wt%) blend, with liquid natural rubber-graft-methy methacrylate (LNR-g-MMA) of 0.0, 2.5, 5.0, and 10.0 phr as compatibilizers, were prepared by internal mixing and compression molding. The effect of LNR-g-MMA content on the morphology, mechanical properties, water absorption, thermal degradation, and a lifetime of blends based on PLA and PP was investigated. Scanning electron microscopy (SEM) revealed that the PLA/PP blend underwent phase separation, and the presence of LNR-g-MMA in the PLA/PP blend showed a more homogenized and refined blend morphology. Hence, the addition of LNR-g-MMA was used as a compatibilizer to induce miscibility in the PLA/PP blend. The values of tensile strength, elongation at break, and impact strength of the polymer blends increased, whereas water absorption values decreased with increased LNR-g-MMA content. Thermal degradation kinetics was studied over a temperature range of 50-800 °C with multiple heating rates. The results demonstrated that the thermal stability of blends without LNR-g-MMA was greater than that of blends with LNR-g-MMA and that the thermal stability decreased with increasing LNR-g-MMA content. The activation energy (Ea) was calculated by using the Kissinger-Akahira-Sunose method. The Ea value of PLA was much lower than that of PP, and incorporating PP in the PLA matrix increased the Ea. The addition of LNR-g-MMA to the PLA/PP blend decreased the Ea. The lifetime of PLA/PP blends was reduced with the addition of LNR-g-MMA.

Effects of compositional parameters on morphology and rheological properties of HDPE/PVA blends

AbstractPolymeric blends are relevant for research and industry because of their versatility, being able to accomplish property tailoring with competitive cost and ease to scale up, when compared to the development of in‐reactor new polymers. Blends of thermoplastics, however, might have their morphology and properties altered upon processing, therefore, there is uncertainty to some outputs after melt processing. Therefore, having a fixed morphology that is capable of being further processed without significant changes have industrial and academic value. This work presents a comprehensive study of rheological properties and morphology of a selectively crosslinked blend of polyethylene (HDPE) and poly(vinyl alcohol) (PVA), where the effect of the following parameters are evaluated: dispersed phase (PVA) weight fraction, continuous phase (HDPE) rheological properties, compatibilizer (PE‐g‐MAh) and crosslinking agent (maleic anhydride) content. Overall, melt complex viscosity and elasticity have increased with PVA weight fraction and HDPE viscosity. The compatibilizer content has not severely affected melt rheology, although it influenced blend morphology. Crosslinking agent content affected melt rheology and glass transition temperature in a complex way due to the probable competition of some phenomena (crosslinking and reaction vs reduction of crystallinity degree and H bond attenuation), with little effect over PVA morphology.