Microfibrillar Morphology Research Articles

Assessing compatibility, tansesterification, and disintegration of PET/PLA fiber blend in composting conditions

To recycle a blend of PET and PLA, understanding the challenging issues and crucial parameters that affect the properties and morphology of the blend is key to successful recycling. So, the main focus of this study was to investigate the parameters that influence the processability, compatibility, morphology, properties, and disintegration of PET/PLA blend fibers. Using surface tension measurements, acceptable adhesion between the two components was observed. SEM results showed that the PET/PLA blend fibers have a microfibrillar morphology. Based on 1H NMR analysis, the exchange reaction resulted in a block copolymer. The crystallization process in the fibers became more difficult as the PLA content increased due to the formation of copolymers through transesterification. The presence of oriented crystals in the melt-spun fiber blend was confirmed by X-ray diffraction patterns. As the PLA content increased, the tensile strength of the blends decreased gradually. Furthermore, the sample containing 20 wt% PLA exhibited the highest dimensional stability. The disintegration process in composting conditions for PET was improved by PLA.

Investigation the effect of processing condition and dispersed phase content on rheology–morphology relationship in polypropylene/polyethylene terephthalate microfibrillar composite

AbstractMorphological evolutions during the production of microfibrillar composites can be investigated by considering two main steps: (1) the melt blending in the extruder and (2) the drawing process. Deformation, coalescence and break‐up of dispersed phase droplets under shear and elongational flow fields applied in these two main steps lead to the formation of fibrillar morphology. Therefore, it can be stated that the fibrillar morphology is controlled by dispersed phase content, rheological and interfacial properties of the components as well as dispersed phase domains relaxation. In this study, the effect of dispersed phase content on the morphology of the polypropylene/polyethylene terephthalate microfibrillar composite was investigated. Also, three following processing parameters were considered to evaluate the kinetics of in‐situ formation of the microfibrils: Extruder die temperature, water bath temperature and the drawing path length. Linear and nonlinear rheological tests were used as an efficient tool to investigate the rheology–morphology relationship. Among the processing parameters studied, the drawing path length and die temperature had the most and least effect on microfibrillar morphology, respectively. By increasing the drawing path length from 20 to 30 cm, the break‐up of the fibrils and non‐uniformity in the cross section of the fibrils caused a weaker strain recovery after stress removal and also a rapid reduction of stress after cessation of steady shear flow field. Increasing the die temperature has a similar but weaker effect on the final morphology. The rheological results in the linear viscoelastic range all indicated the formation of a physical network of microfibrils within the matrix.

Morphology and Properties of Polyolefin Elastomer/Polyamide 6/Poly(lactic Acid) In Situ Special-Shaped Microfibrillar Composites: Influence of Viscosity Ratio.

In Situ microfibrillation is an easy and economical processing method, which has drawn wide concern in recent years. In Situ special-shaped microfibrillar composites, which with poly(lactic acid)/polyamide 6 (PA6/PLA) together formed special-shaped microfibrils in polyolefin elastomer (POE) matrix, were successfully prepared by using multistage stretching extrusion technology. Four types of PA6 with different viscosity were utilized to investigate the effect of viscosity ratio of PA6 to PLA on the structure evolution of special-shaped microfibrils and the mechanical properties of POE/(PA6/PLA) composites. The morphological observation showed that the viscosity ratio was closely associated to the size and shape of PA6 and greatly affected the microfibrillar morphology of PLA/PA6. When the viscosity ratio of PA6 to PLA was less than 2.2, the "gourd-skewers-like" structure microfibrils were obtained. When the viscosity ratio of PA6/PLA to 14.2 was further increased, the "trepang" structure microfibrils were dominant. The "gourd skewers" structure microfibrils were favorable to improvement the tensile strength, Young's modulus, and viscoelastic properties of POE/(PA6/PLA) blends compared to the "trepang" structure microfibrils. In addition, the morphology of microfibrils exhibited a negligible effect on the melting and crystallization temperature and crystallization degree of PLA and POE matrix. This work provides a new strategy for designing the in situ special-shaped microfibrillar composites with improved mechanical properties.

Additive Manufacturing of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Poly(D,L-lactide-co-glycolide) Biphasic Scaffolds for Bone Tissue Regeneration.

Polyhydroxyalkanoates are biopolyesters whose biocompatibility, biodegradability, environmental sustainability, processing versatility, and mechanical properties make them unique scaffolding polymer candidates for tissue engineering. The development of innovative biomaterials suitable for advanced Additive Manufacturing (AM) offers new opportunities for the fabrication of customizable tissue engineering scaffolds. In particular, the blending of polymers represents a useful strategy to develop AM scaffolding materials tailored to bone tissue engineering. In this study, scaffolds from polymeric blends consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(D,L-lactide-co-glycolide) (PLGA) were fabricated employing a solution-extrusion AM technique, referred to as Computer-Aided Wet-Spinning (CAWS). The scaffold fibers were constituted by a biphasic system composed of a continuous PHBV matrix and a dispersed PLGA phase which established a microfibrillar morphology. The influence of the blend composition on the scaffold morphological, physicochemical, and biological properties was demonstrated by means of different characterization techniques. In particular, increasing the content of PLGA in the starting solution resulted in an increase in the pore size, the wettability, and the thermal stability of the scaffolds. Overall, in vitro biological experiments indicated the suitability of the scaffolds to support murine preosteoblast cell colonization and differentiation towards an osteoblastic phenotype, highlighting higher proliferation for scaffolds richer in PLGA.

EcoBlends’up: PLA/BioPA blends composites, microfibrillated “in situ” through additive manufacturing

In certain polymer blends, a properly oriented microfibrillar morphology of the dispersed phase during the processing stage can generate a reinforcing effect by increasing the fracture toughness, especially in the crack propagation stage. These types of materials are called “in situ” microfibrillated composites (MFCs). Its obtention is conditioned by the rheological properties of the blend and the parameters of the forming process. In this context, additive manufacturing is of interest, specially fused filament fabrication (FFF) by pellets supply instead of extruded filaments. In this work, the study of the feasibility of manufacturing MFCs is proposed by inducing the microfibrillation of a BioPA in the PLA/BioPA “ecoblends”. The optimal processing conditions of the FFF process for the generation of MFCs are evaluated, as well as the uniaxial tensile behavior and the fracture behavior of the manufactured SENB test specimens, employing instrumented impact technique. The evidence obtained shows that the use of a rheologically modified PLA matrix by reactive extrusion (PLAREX) promotes the obtention of MFCs with a better balance of mechanical properties in terms of elastic modulus (E) and ductility and an improvement in apparent toughness and resistance to crack propagation of the fabricated part.

РЕГУЛЮВАННЯ СТІЙКОСТІ РІДКИХ МІКРОСТРУМЕНІВ ПОЛІПРОПІЛЕНУ В МАТРИЦІ СПІВПОЛІАМІДУ ЗА РАХУНОК НАНОДОБАВОК

Goal. Investigation of the effect of the concentration of nanoparticles of aluminum oxide (Al2O3) and alumina modified with silver (Ag/Al2O3) on the decomposition kinetics of liquid microjets of polypropylene (PP) in a copolyamide (CPA) matrix and the possibility of controlling the microfibrillar morphology of the PP/CPA blend.Methodology. The components of the blend were mixed on a screw-disk extruder. The kinetics of the disintegration of liquid microjets was studied using a technique based on the theory of destabilization of a liquid cylinder under the action of capillary waves. The degree of dispersion of polypropylene in the matrix was evaluated by photomicrographs of cross sections of the extrudates of the blends.Results. Nanoadditives of the original and silver-modified aluminum oxide with a content of (0.1 ÷ 3.0) wt.% In the blend increase the compatibility of the components: the surface tension (γαβ) in the compositions of all compositions decreases. Ag/Al2O3 nanoparticles are more effective than aluminum oxide nanoparticles - the γαβ value decreases by 9.6 and 5.3 times, respectively, which ensures a high degree of dispersion of the dispersed phase component in the matrix. The disintegration resistance of polypropylene microjets is increasing, as evidenced by a decrease in the instability coefficient (q) and an increase in the microjet lifetime (tl). The curves of q and tl dependence on the additive content have an extreme character. The minimum values of the instability coefficient of microjets and the maximum values of their lifetime are achieved at a nanoparticle concentration corresponding to the lowest interfacial tension.Scientific novelty. The positive effect of the investigated nanoadditives on the kinetics of the decomposition of liquid microjets of polypropylene in the copolyamide matrix has been established. The highest modifying effect in the presence of Ag/Al2O3 nanoparticles is due to their amphiphilic nature, which ensures the predominant localization of nanoparticles at the interface and a synergistic increase in the degree of compatibility in the PP/CPA system.Practical significance. The regularities of increasing the stability of liquid microjets to disintegration in polymer blends filled with nanoparticles have been established, which will make it possible to determine the parameters of the processes of mixing and forming fibers and films, in which the microfibrillar structure arising during the flow of the melt will remain unchanged in the products.

Strong, Ultrafast, Reprogrammable Hydrogel Actuators with Muscle-Mimetic Aligned Fibrous Structures

Hydrogel actuators displaying programmable shape transformations promise to be core components in future biomedical and soft robotic devices. However, current hydrogel actuators have shortcomings, including poor mechanical properties, slow response, and lack of shape reprogrammability, which limit their practical applications . Existing molecular designs offer limited efficiency in synergistically addressing these issues in a single hydrogel system. Herein, we propose a strategy to develop hydrogel actuators with muscle-mimetic aligned microfibrillar morphology, combining thermoinduced microphase separation and mechanical alignment. The key to our design is the introduction of metal–phenolic complexes, which not only induce irreversible sol–gel transition via the concentrated coordinate ions above lower critical solution temperature (LCST) but also fix the alignment of bundle network due to dynamic network rearrangement. Our design concept is observed to simultaneously achieve excellent mechanical properties (tensile strength ≈ 1.27 MPa, toughness ≈ 2.0 MJ m–3) and ultrafast actuation (40.1% thermal contraction as short as 1 s), which is a long-lasting challenge in the field. In addition, the dynamic hydrogels can be reprogrammed into spiral, helical, and biomimetic actuators. This work opens new opportunities to realize real-world applications for smart hydrogels as soft machines by fundamentally breaking the current property limit.

Rheology–morphology interrelationship in high-density polyethylene/polyamide-6 microfibrillar composites

Due to the importance of rheology and morphology of microfibrillar reinforced composites (MFCs), a study has been conducted on MFCs based on high-density polyethylene (HDPE) and polyamide-6 (PA-6) using scanning electron microscope and dynamic rheometer. In the absence of an interfacial modifier and at 10 wt% concentration of the dispersed phase (PA-6), two principal factors, elongational deformation and coalescence, were found to be controlled by viscosity and elasticity ratios of the pure constituents accounting for the observed morphology of MFCs. The developed microfibrillar morphology remarkably influenced the viscoelastic properties of MFCs. It was observed that when the viscosity ratio approached unity and the elasticity ratio was minimal, the extent of coalescence in composite was significant. The rheological assessment showed enhanced storage modulus and complex viscosity upon microfibrils formation. This was more pronounced for samples with thinner microfibrils due to more strongly entangled network, compared to the composites with thicker microfibrils. The length-to-diameter ratio of the microfibrils could not be estimated due to their highly asymmetric length scale.

Effect of multi-step processing on the structural, morphological and dielectric behaviour of PVDF films

In this work, we have reported the systematic preparation of flexible and transparent PVDF films, through multi-step processing techniques including solvent casting followed by thermal compression and mechanical stretching. Variation in the structural, morphological and dielectric behaviour of each film with respect to each processing condition are analysed through FTIR, XRD, DSC, FESEM, AFM and impedance spectroscopy. The structural characterisation revealed the deep influence of thermal compression and mechanical stretching process on the electroactive s-phase structure of solvent-casted PVDF films while the morphological analysis confirmed the formation of microfibrillar morphology after three successive processing methods. A significant increment in the dielectric constant value from 10.7 (for solvent-casted PVDF film) to 24 (for solvent-casted followed by thermal compression followed by mechanical stretched PVDF film) and dielectric loss of 0.015 to 0.0018 has achieved for PVDF film after multi-step processing techniques. Such improvements in structural and dielectric behaviour are attributed to the thermo and mechanical dependent changes in the crystalline structure which helps in the rotation of polar –CH2-CF2 group.

Effect of stretching speed on morphologies and properties of in situ microfibrillar POE/PLA composites

In situ microfibrillar ethylene–octene copolymer (POE)/poly(lactic acid) (PLA) composites (MFCs) with different phase morphologies were prepared by controlling the stretching speed and maintaining the weight ratio of POE/PLA of 80/20. Four different stretching speeds were employed to study the effect of PLA microfibrillar morphology on tensile, crystalline, and rheological properties of MFCs. Scanning electron microscopic images revealed that the morphology of PLA phase was strongly influenced by stretching speed. MFCs with highest aspect ratio and smaller diameter of PLA microfibrils were obtained with a stretching speed of 60 rpm. The PLA microfibrils with high aspect ratio had the best reinforcement effect on MFCs. The dynamic rheological properties indicated that the MFCs achieved higher storage modulus and loss modulus at the stretching speed of 60 rpm.

Morphology, Rheology and Crystallization in Relation to the Viscosity Ratio of Polystyrene/Polypropylene Polymer Blends.

Microfibrillar and droplet morphology of polypropylene (PP) phase dispersed in polypropylene (PS) was fabricated by using melt-extrusion. This morphology was obtained by introducing isotactic PP (20 wt.%) with different viscosity in the PS matrix (80 wt.%). Furthermore, the rheological properties of the blend investigated as a function of the viscosity ratio K. The variations in blend morphology were related to crystallization, melting properties, and viscoelasticity. The blends with K >> 1 develop a fine morphology with PP microfibrils along the flow direction, while diameters of the dispersed PP droplets gradually increase with lower values of K = 1, or K << 1. Crystallinity of the prepared blends significantly decreases compared to neat PP, while the microfibrillar morphology induces homogeneous crystallization with small crystallites. This is reflected in a decrease of the crystallization temperature, small loss in the crystallinity, and lower melting temperature of the PS80/PP20 blend compared to neat PP. The storage moduli, loss moduli, and complex viscosity are highest for the microfibrillar morphology that presents retarded relaxation. The rheological properties are dominated by the dispersed phase (K > 1), or matrix (K < 1). The variation in blend properties with microfibrillar morphology can be clearly distinguished from heterogeneous blends containing PP droplets, providing an efficient tool to create a binary blend with unique properties.

An efficient fabrication of polypropylene hybrid nanocomposites using carbon nanotubes and PET fibrils

In this particular study, Polypropylene (PP)/Polyethylene terephthalate (PET)-Multiwall carbon nanotubes and microfibrillar reinforced nanocomposites (MFNC-C) have been fabricated via melt mixing-extrusion-cold drawing-compression moulding. The electrical conductivity, static mechanical properties have been discussed. Microfibrillar morphology, synergetic effect on the electrical conductivity, tensile strength, tensile modulus of the MFNC-C and EBNC-C were investigated. Microstructure analysis confirms that selective localisation of MWCNTs and fibrils morphology plays a pivotal role to boost the overall performance of PP.

Physical and Mechanical Properties of Wood-Plastic Composites Made with Microfibrillar Blends of LDPE, HDPE and PET

The effect of microfibrillar blends of recycled plastics on selected physical and mechanical characteristics of wood-plastic composites (WPCs) was investigated in this study. The production of wood plastic composites was carried out through a two-step extrusion technique. The plastic blends were drawn after extrusion to obtain microfibrillar morphology. The addition of polyethylene-co-glycidyl methacrylate (E-GMA) enhanced compatibility between the two phases and a homogenous structure was seen in the fracture surfaces by scanning electron microscopy (SEM). The crystallinity of base polymers increased with the addition of polyethylene terephthalate (PET) microfibrils, E-GMA and wood flour. The X-ray diffraction (XRD) patterns were also used to determine the crystallinity of all samples. According to the XRD results, the crystallinity degree of recycled plastics was higher than that of virgin plastics. E-GMA improved the water resistance of wood-plastic composites. The mechanical properties of samples were improved with the addition of PET microfibrils. The microfibrillar blending technique was found to be an effective approach for the production of high quality WPCs from recycled plastic blends.

Semiconducting 2D Triazine-Cored Covalent Organic Frameworks with Unsubstituted Olefin Linkages

Establishing an sp2-carbon-bonding pattern is one of the efficient accesses to various organic semiconducting materials. However, the less-reversible carbon-carbon bond formation makes it still challenging to spatially construct a well-defined organic framework with π-extended two-dimensional (2D) structure through solution process. Here, a Knoevenagel condensation approach to synthesize two new 2D covalent organic frameworks (COFs) connected by unsubstituted carbon-carbon double bond linkages through activating the methyl carbons of a 2,4,6-trimethyl-1,3,5-triazine monomer is presented. The resulting sp2-carbon-linked triazine-cored 2D sheets are vertically stacked into high-crystalline honeycomb-like structures, endowing this kind of COF with extended π-delocalization, tunable energy levels, as well as high surface areas, regular open channels, and chemical stabilities. On the other hand, their microfibrillar morphologies allow for the facile manipulation of thin films as photoelectrodes without additive. Accordingly, such kinds of COF-based photoelectrodes exhibit photocurrents up to ∼45 μA cm-2 at 0.2 V vs RHE as well as rapid charge transfer rates, in comparison with imine-linked COF-based photoelectrodes. In addition, both COFs are applicable for conducting photocatalytic hydrogen generation from water splitting by visible-light irradiation.

Simultaneously reinforce and toughen polypropylene by in‐situ introducing polylactic acid microfibrils

A petroleum‐based polymer, isotactic polypropylene (iPP), and a biodegradable polymer, poly(lactic acid) (PLA), were compounded and molded into parts through the micro‐injection technique. A systematic structural investigation indicated that the microfibrillation of PLA minor phase depended on the operation parameter of inter‐mixer, ie, rotor speed. The higher rotor speed, the lower viscosity ratio of the PLA/iPP pair was favorable for microfibrillation occurred during micro‐injection process. The PLA microfibrils with high aspect ratio was successfully introduced into iPP matrix, and the tensile strength and strain at break of iPP/PLA blends were simultaneously improved. This study suggests a promising method for designing special microfibrillar morphology in polymer blend by using conventional melt processing techniques.

The Effect of Blending Sequence on Nanoclay Partitioning and Microfibrillar Morphology in Blend Nanocomposite Fibers

ABSTRACTThe aim of this article was to provide an insight into the effect of nanoclay partitioning on the droplet deformation and fibril formation in melt-compounded polypropylene/poly (butylene terephthalate)/organoclay blend nanocomposite fibers prepared by different blending sequences. An attempt was also made to investigate the effect of compatibilizer on the partitioning of nanoclay in these blend systems. Melt viscoelastic behavior, wide angle X-ray diffraction and transmission electron microscopy, along with scanning electron microscopy, revealed that the localization of nanoclay in the poly (butylene terephthalate) dispersed phase reduced the droplet deformation and fibril formation. It was demonstrated that the best microstructure of the blend nanocomposites for the fibrillation process was to have the maximum percentage of exfoliated nanoclay in both polymeric phases. Incorporation of compatibilizer can develop the microfibrillar morphology due to its assisting role in transferring a higher fraction of nanoclay platelets from droplets into the matrix and also increasing the extent of melt intercalation in the matrix.

Relationship between dye sorption and morphology in polypropylene/poly (butylene terephthalate) microfibrillar blend nanocomposite fibers

In this research work, the relation between microstructural enhancement and dyeing behavior of immiscible blend nanocomposite fibers was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction patterns, and rheometric mechanical spectrometer along with quantitative analysis of dye sorption. A novel microfibrillar morphology blend fiber, in which poly (butylene terephthalate) nanocomposite fibrils uniformly distributed in the cross section of polypropylene matrix, was successfully developed using melt compounding process. Preferred location of nanoclay had improving effect on poly (butylene terephthalate) fibril formation such that there was an organoclay concentration above that fiber with fine microfibrillar morphology could hardly be produced. It was demonstrated that nanoclay melt intercalation and partitioning controlled the activation energy of dyeing. The maximum sorption rate was achieved by utilizing compatibilizer to transfer part of nanoclay platelets into the polypropylene matrix.

Prenatal developmental safety of functional polyurethanes for cardiovascular implants.

Historically, polyurethanes have been regarded as promising materials for cardiovascular implants such as vascular grafts and heart valves. Their biocompatibility has been thoroughly investigated. However, their developmental toxicity is seldom reported. We recently developed two polycarbonate urethanes with polyethylene glycol side chains capped with epoxy or amino groups that can further react with specific biomolecules. Both materials in microfibrillar morphology were subjected to saline extraction at 70 °C to prompt material hydrolysis. Proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography all confirmed the degradation of the polyurethanes. The saline extracts containing the degradation products were administered to Sprague-Dawley female rats on day 7 to 16 of gestation via tail vein injection at a dose of 5 mL/kg/day. No maternal toxicity was observed. No external, skeletal, and visceral malformations in fetuses were found associated with the test materials, implying their safety to both adult rats and the offspring. Further investigations for applications in vascular grafts are under way.

Effects of initial crystallization process on piezoelectricity of PVDF-HFP films

Abstract The effects of some important factors in the initial crystallization process of the solution casting method on the piezoelectricity of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) films were extensively explored. The experimental results revealed that there is an optimal initial crystallization temperature at around 90°C. The slow cooling speed can moderately enhance the degree of crystallinity. The most important finding was that a bilayer crystalline structure caused by an asymmetrical heating pattern can enhance the formation of packed micro-fibrillar morphologies after drawing. These three points can increase the piezoelectricity of the PVDF-HFP films, indicating the increase of the extended-chain crystals (β-phase).

The role of nanoclay partitioning and fibril formation on dyeability of blend nanocomposite fibres

The aim of the present work was to study the effect of microstructure and microfibril formation on dyeability of polypropylene/poly(butylene terephthalate)/organoclay blend nanocomposite fibres. The blend nanocomposite samples with the same blend ratio but varying in organoclay content were prepared via melt compounding by using a co‐rotating twin screw extruder. The microfibrillar morphology and nanoclay partitioning were studied using scanning electron microscopy and transmission electron microscopy together with rheological results. The presence of nanoclay in the form of tactoids in the polypropylene matrix accelerated the dye sorption but much greater ultimate dye uptake could be achieved for the sample in which the major part of the platelets were preferentially located inside the poly(butylene terephthalate) fibrils. Although increasing the organoclay concentration increased the ultimate dye uptake, it limited the fibril formation at higher organoclay concentration. The utilisation of a compatibiliser was found to have an enhancing effect on ultimate dye uptake. This could be explained in terms of the interfacial role of the compatibiliser in improving microfibril formation as well as partitioning a fraction of nanoclay platelets inside the polypropylene matrix.