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Polyethylene terephthalate (PET) films were prepared by cast extrusion using a twin-screw extruder with a severe screw profile. The effect of an organically modified montmorillonite on thermal, mechanical, optical, and barrier properties of the PET films were investigated. Morphological characterization of the nanocomposite films was performed by employing wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) followed by image analysis. The results unfold a mixed morphology for the nanocomposite films with more than 95% exfoliated and intercalated silicate layer structures, depending on the screw rotation speed. The remarkable dispersion of the organoclay particles at the nano-level is discussed in terms of solubility parameter and favorable interactions between PET macromolecules and organic modifier of the nanoclay. The crystal content of the nanocomposite films and their cold and hot crystallization temperatures confirmed the role of silicate nanolayers as a heterogeneous nucleating agent. While all nanocomposite films exhibit higher haze values in comparison to the neat PET samples, incorporation of 2 wt% nanoclay brought about 25% increase in tensile modulus and barrier properties. A range of screw rotation speeds with optimized properties in terms of haze, morphology, thermal, mechanical, and barrier properties is suggested.

The importance of conformational rigidity on macroscopic rheological properties was revealed using two model polysaccharides, namely, xanthan gum and hyaluronic acid. Xanthan gum has a rigid tertiary conformation due to its ordered double-helical structure, and the interactions between the tertiary structures result in the formation of a network/quaternary structure. In comparison, hyaluronic acid possesses a relatively flexible tertiary conformation due to its secondary random coil structure. Xanthan gum exhibits a much stronger shear thinning and more solidlike behavior compared to hyaluronic acid, owing to its network/quaternary structure. The rigid tertiary structure and the presence of a network/quaternary structure also endow xanthan gum with better resistance against environmental changes (e.g., salt and/or urea addition, temperature change) compared to hyaluronic acid. The network/quaternary structure allows xanthan gum to form gels with chitosan via electrostatic interactions when using the vapor-induced gelation technique, which is not possible for hyaluronic acid due to its flexible tertiary conformation under similar conditions.

Blends containing 85 wt. % of an amorphous polylactide with 15 wt. % of three different semicrystalline PLA (cPLA) grades with different crystallizabilty were separately blended via a twin-screw extruder below the melting temperature of the cPLAs. The extrudates were either directly pelletized or pelletized after being drawn at a draw ratio of 10. The small amplitude oscillatory shear behavior of the samples revealed that while the rheological properties of the undrawn samples were enhanced, those of the drawn samples were much more dramatically increased. In undrawn samples, the enhancements were due to the presence of unmelted crystal clusters, which could form a solid network structure in the blend. The much more pronounced increases in drawn samples, however, were due to the transformation of the crystal clusters into the fiberlike oriented crystal network, which formed a stronger solid network. This reinforcing behavior in both undrawn and drawn samples was even more pronounced when cPLA with a higher degree of crystallinity and a higher melting temperature was used. In drawn samples, the stress growth experiments confirmed the formation of such oriented crystal structure during which the primary overshoot caused by the crystal network structure could be formed again after molecular relaxation. This was while, in undrawn samples, stress overshoots were barely visible.

Blends of a poly(butylene adipate-co-terephthalate) (PBAT) and a low density polyethylene (LDPE) (80 wt%/20 wt%) were prepared through a twin screw extruder while incorporating 3 wt% Cloisite 30B (C30B) nanoclay that possessed a much higher affinity with PBAT. The blends were processed through three melt mixing strategies: ( i) direct mixing of all three components, (ii) mixing C30B and PBAT followed by mixing with LDPE, and (iii) mixing C30B and LDPE followed by mixing with PBAT. The rheological properties of each system were determined in small amplitude oscillatory shear (SAOS) experiments. The migration of C30B nanoparticles from the LDPE minor phase towards the PBAT matrix was then monitored in the blend nanocomposites prepared through strategy (iii) via SAOS time sweep experiments. It was firstly understood that the C30B migration could be detected during time sweep SAOS experiments. The migration time was observed to be frequency dependent due to the smaller length scales probed at larger frequencies. Such migration occurred even faster when the SAOS time sweep experiments were conducted at a higher temperature due to the viscosity reduction.

International audience; In this study, multiwall carbon nanotubes (MWCNTs) and double-wall carbon nanotubes (DWCNTs) have been dispersed in polylactide (PLA) and polyamide 11 (PA11) using an internal mixer. Rheological characterization confirmed the formation of carbon nanotube (CNT) networks in PLA and PA11 attributed to well-dispersed CNTs in the respective matrices. A lower rheological percolation threshold of PLA/ MWCNT nanocomposites (less than 0.5 wt. %) compared to PA11/MWCNT nanocomposites (about 2 wt. %) confirmed the greater affinity of CNTs for PLA. The threshold for DWCNTs was below 0.5 wt. % in PLA and between 0.5 and 1 wt. % in PA11. PLA-based nanocomposites also showed higher electrical conductivity values compared to PA11-based nanocomposites. Nanocomposites containing DWCNTs exhibited higher electrical conductivities compared to those containing MWCNTs due to the higher aspect ratio of DWCNTs. Dynamic mechanical thermal analysis showed enhanced storage modulus values and reduced damping behavior with increasing content of CNTs for both polymers.

Poly (lactic acid) or polylactide (PLA) is a commercial biobased, biodegradable, biocompatible, compostable and non-toxic polymer that has competitive material and processing costs and desirable mechanical properties. Thereby, it can be considered favorably for biomedical applications and as the most promising substitute for petroleum-based polymers in a wide range of commodity and engineering applications. However, PLA has some significant shortcomings such as low melt strength, slow crystallization rate, poor processability, high brittleness, low toughness, and low service temperature, which limit its applications. To overcome these limitations, blending PLA with other polymers is an inexpensive approach that could also tailor the final properties of PLA-based products. During the last two decades, researchers investigated the synthesis, processing, properties, and development of various PLA-based blend systems including miscible blends of poly l-lactide (PLLA) and poly d-lactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This article reviews all these investigations and compares the syntheses/processing-morphology-properties interrelationships in PLA-based blends developed so far for various applications.

Morphological and rheological properties of poly(lactic acid), PLA (semicrystalline and amorphous), and poly(butylene adipate-co-terephthalate), PBAT, and their blends (75 wt%/25 wt%, PLA/PBAT) were investigated in the presence of cellulose nanocrystals (CNCs) prepared from solution casting followed by melt mixing. For the solution casting step, the CNCs were either incorporated into the matrix, the dispersed phase, or both. The dispersion and distribution of the CNCs in the neat polymers and localization in their blends were analyzed via scanning electron microscopy (SEM) and atomic force microscopy (AFM). The highly dispersed CNCs in the solution cast nanocomposites were agglomerated after melt mixing. In the blends with 1 wt% CNCs, the nanoparticles were mostly localized on the surface of the PBAT droplets irrespective of their initial localization. The rheological behavior of the single polymer matrix nanocomposites and their blends was determined in dynamic and transient shear flow in the molten state. Upon melt mixing the complex viscosity and storage modulus of the solution cast nanocomposites decreased markedly due to re-agglomeration of the CNCs. Under shearing at 0.1 s−1, a significant droplet coalescence was observed in the neat blends, but was prevented by the presence of the CNCs at the interface in the blend nanocomposites.

Cellulose nanocrystal (CNC)-based materials display apparently erratic wetting behaviors with contact angle (CA) variations as large as 30° from sample to sample. This work hypothesizes that it is the orientation of CNC amphiphilic functionalities at the interface with air that causes the variability in CA. By exploiting relationships with the Hansen solubility parameter theory, a set of surface tension parameters is proposed for both the polar and the non-polar surfaces of cellulose Iβ nanocrystals. These coefficients elucidate the wettability of CNC materials by establishing a correlation between the wetting properties of the air/sample interface and its chemical composition in terms of non-polar moieties. Advancing/receding CA experiments suggest that, while spin-coating CNC suspensions yield purely polar films, oven-casting them produces amphiphilic surfaces. We proposed a mechanism where the state of dispersion (individual or agglomerated) in which CNCs reach the air/water interface during casting is the determining factor: while individual nanocrystals find it more stable to orient their non-polar surfaces toward the interface, the aspect ratio of CNC agglomerates favors an orientation of their polar surfaces. This represents the first compelling evidence of CNC orientation at an interface and can be applied to Pickering emulsions and nanocomposites and to the production of CNC materials with tuned wettability.

In order for sustainable nanomaterials such as cellulose nanocrystals (CNCs) to be utilized in industrial applications, a large-scale production capacity for CNCs must exist. Currently the only CNCs available commercially in kilogram scale are obtained from wood pulp (W-CNCs). Scaling the production capacity of W-CNCs isolation has led to their use in broader applications and captured the interest of researchers, industries and governments alike. Another source of CNCs with potential for commercial scale production are tunicates, a species of marine animal. Tunicate derived CNCs (T-CNCs) are a high aspect ratio CNC, which can complement commercially available W-CNCs in the growing global CNC market. Herein we report the isolation and characterization of T-CNCs from the tunicate Styela clava, an invasive species currently causing significant harm to local aquaculture communities. The reported procedure utilizes scalable CNC processing techniques and is based on our experiences from laboratory scale T-CNC isolation and pilot scale W-CNC isolation. To our best knowledge, this study represents the largest scale where T-CNCs have been isolated from any tunicate species, under any reaction conditions. Demonstrating a significant step towards commercial scale isolation of T-CNCs, and offering a potential solution to the numerous challenges which invasive tunicates pose to global aquaculture communities.

Hypothesis In solvent casting, colloidal nanocrystal self-assembly patterns are controlled by a mix of cohesive and repulsive interactions that promote destabilization-induced self-assembly (DISA) or evaporation-induced self-assembly (EISA). Tuning the strength and nature of the stabilization mechanisms may allow repulsive interactions to govern self-assembly during the casting of colloidal cellulose nanocrystal (CNC) suspensions. Experiments We propose a tool to classify the level of electrostatic and solvation-induced stabilizations based on two solvent parameters only: dielectric constant, e , and chemical affinity for CNCs, in terms of Hansen Solubility Parameters, R a . These criteria are applied to study CNC self-assembly in solvent casting experiments in various media and binary mixtures. Findings In solvent casting of suspensions stabilized through a combination of electrostatic and solvation effects, the primarily governing mechanism is EISA, which leads to the formation of chiral nematic domains and optically active thin films. In electrostatically-stabilized suspensions, EISA and DISA are in competition and casting may yield anything from a continuous film to a powder. In other suspensions, DISA prevails and evaporation yields a powder of CNC agglomerates. By classifying media according to their stabilization mechanisms, this work establishes that the behavior of CNC suspensions in solvent casting may be predicted from solvent parameters only.

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration.

The rheological behavior of cellulose nanocrystals (CNCs) in polar media based on polyethylene glycol (PEG) was investigated from aqueous suspensions to nanocomposites. The aim of this work is to improve our knowledge on the CNC behavior in polymer media and develop rheological indices to characterize the dispersion of nanoparticles in polymer matrices. CNCs were obtained from sulfuric acid hydrolysis of wood pulp and supplied after a spray- or freeze-drying process. Ultrasonication was used to break agglomerates and disperse CNCs in aqueous suspensions before mixing with an aqueous PEG solution at room temperature. The samples were subsequently dried and compression molded. From capillary and oscillatory shear rheology, no adsorption of PEG chains on CNCs could be detected, as many had previously hypothesized. The increase of PEG concentration in aqueous suspension favored the gelation by depletion effect and suggested CNC orientation. Viscoelastic properties and transmission electronic images of PEG/CNC nanocomposites highlighted the formation of a percolated network of CNCs for low concentrations ≥ 0.15 vol. %. From the model of Shih et al., a fractal dimension of 2 was obtained for these percolated nanocomposites, suggesting a 2D network of CNCs in the PEG matrix.

The rheological behavior of cellulose nanocrystal (CNC) and modified CNC (mCNC) suspensions in dimethyl sulfoxide (DMSO) was investigated. The efficiency of the surface modification of CNCs by grafting an organic acid chloride to produce hydrophobic CNCs has been verified by X-ray photoelectron spectroscopy (XPS). The thermal degradation temperature of the mCNCs was found to be 165 versus 275 °C for CNCs. The CNC suspensions in DMSO at 70 °C underwent gelation at very low concentration (1 wt%) after 1 day. The network formation was temperature sensitive and did not occur at room temperature. For gels containing 3 wt% CNCs, the complex viscosity at 70 °C increased by almost four decades after 1 day. For the mCNCs in DMSO, a weak gel was formed from the first day and temperature did not affect the gelation. Finally, the effect of adding 10 wt% of polylactide (PLA) to the solvent on the rheological properties of CNC and mCNC suspensions was investigated. The properties of suspensions containing 1.9 wt% CNCs and mCNCs increased during the first and second days, and PLA did not prevent gel formation. However, the reduced viscosity and storage modulus of the CNC and mCNC gels with PLA were lower than those of samples without PLA.

Polylactide (PLA)/cellulose nanofiber (CNF) biocomposites were prepared via solution casting and direct melt mixing. To improve the compatibility, a masterbatch of CNFs and poly(ethylene glycol) (PEG) (1:2) was also prepared. The effects of PEG on the morphology and properties of the biocomposites were investigated. The dispersion/distribution of nanofibers in PLA was improved when the masterbatch was used and the composites were prepared in solution. Substantial effects on the rheological properties of solution-prepared PLA/CNF/PEG composites were observed compared to composites containing no PEG, whereas for melt-prepared composites no significant changes were detected. Increased crystalline content and crystallization temperature were observed for the composites prepared via the masterbatch and solvent casting. The storage modulus of PLA was increased by 42 and 553% at 25 and at 80 °C, respectively, for the solution-based PEG-compatibilized composite containing 2 wt% nanofibers. Also, a better light transmittance was measured for the PLA/CNF/PEG composites prepared in solution.

Blends of 75 wt% amorphous polylactide (PLA) with 25 wt% poly[(butylene adipate)-co-terephthalate] (PBAT) and poly[(butylene succinate)-co-adipate] (PBSA) were prepared. The effects of PLA molecular weight and of two different mixing processes (i.e., internal mixer and twin-screw extruder) on the blend properties were investigated. The crystallization behavior, rheological properties, and morphology of these blends and neat polymers were firstly examined. The tensile properties and bead foaming behavior of the neat and blend systems were then investigated. Various blend morphologies could be obtained by using different molecular weight PLAs as well as different processing techniques. The tensile properties of the blends were significantly affected by the droplet size and PLA matrix molecular weight. Different microcellular bead foam structures ranging from low-density open-cell to high-density closed-cell were manufactured by using blends with different droplet morphologies as well as by using minor phase solid inclusions with different rigidities originated from different crystallization behavior.

A universal approach to gain control over molecular interactions among activated, ready-to-react monomers, e.g., ammonium zirconium carbonate, has been proposed in which the monomers bind to two families of nanoengineered celluloses, namely hairy and conventional nanocelluloses with various surface functionalities and steric and electrosteric moieties. Engineering the colloidal interactions, the polymerization reaction was tailored to yield a spectrum of ultrasoft (5 decades decrease in viscoelastic moduli) to highly-reinforced (4000% enhanced viscoelasticity) nanocomposites using only 0.5 wt% nanoparticles.

Sagging in paints is mainly governed by rheology. In this work, two methods are proposed to predict the Anti-Sag Index of paints (ASTM D4400) based on the rheological analysis of the sag flow. Both methods provide good predictions with a characteristic velocity in the range of 400−600 μm/s. The maximum difference between the predicted values of the Anti-Sag Index and the observed ones is ∼2 mils. The viscoelastic properties of paints have also been examined, and a strong correlation is found between the Anti-Sag Index and the elastic modulus in the linear regime, G’, especially the one measured at time zero, immediately after pre-shear, probably because it is more representative of the paint behavior right after the application and the onset of the drying process.

Poly(ethylene oxide) (PEO)/cellulose nanofiber (CNF) biocomposites were developed using a simple aqueous solution technique. A PEO/CNF composite was also produced in the molten state to compare different preparations. The effects of nanofibers on different properties of PEO including rheological, thermal, mechanical and optical were investigated. For the sample prepared in the molten state, no change in properties was observed as compared to the neat matrix. On the other hand, for the solution-based samples, scanning electron microscopy revealed good dispersion/distribution of nanofibers in the PEO, which resulted in a significant increase of the rheological properties and also a notable shear-thinning behavior. A liquid- to solid-like behavior transition along with the observation of apparent yield stress suggested the formation of a strong CNF 3D network. The Young’s modulus and tensile strength of PEO with 3 wt% CNFs were enhanced by 49 and 35%, respectively, compared to the neat PEO. The storage modulus of PEO was significantly improved for all tested temperatures in the dynamic mechanical thermal analysis; at room temperature that corresponds to the rubbery region, a 47% enhancement was observed by incorporating 3 wt% nanofibers. Also, PEO/CNF composites demonstrated good optical transmittance, which is generally not the case with many reinforcements. These results show that PEO/CNF biocomposites with good mechanical and optical properties can be fabricated via a simple aqueous solution technique.

Blends of an amorphous polylactide (PLA) with 25 wt% poly[(butylene adipate)-co-terephthalate] (PBAT) containing 1 and 5 wt% Cloisite 30B (C30B) nanoclay were prepared using an internal batch mixer. Three mixing strategies were used: (S1) direct mixing of all three components, (S2) mixing C30B and PLA followed by mixing with PBAT, and (S3) mixing C30B and PBAT followed by mixing with PLA. X-ray diffraction (XRD) and transmission and scanning electron microscopy (TEM and SEM) were used to study the C30B dispersion and the blend morphology. Small amplitude oscillatory shear (SAOS) and stress growth tests were also conducted to investigate the nanocomposites and blend rheological properties and morphological stability under shear flow. With 1 wt% C30B, the nanoparticles were located at the PLA-PBAT interface for all mixing routes, which was favorable for morphology stabilization. The average PBAT droplet-diameter was reduced from 1.30 μm for the neat PLA-PBAT blend to 0.75, 0.85, and 0.70 μm for blend nanocomposites depending on the mixing strategy used. Under shearing at 0.01 s−1, droplet coalescence did not occur due to the presence of C30B at the interface of the polymer phases. On the other hand, in blends containing 5 wt% C30B, the location of the nanoparticles and the occurrence of coalescence depended on the mixing strategy used.

Blends containing 75 wt. % of an amorphous polylactide (PLA) with two different molecular weights and 25 wt. % of a poly[(butylene adipate)-co-terephthalate] (PBAT) were prepared using either a Brabender batch mixer or a twin-screw extruder. These compounds were selected because blending PLA with PBAT can overcome various drawbacks of PLA such as its brittleness and processability limitations. In this study, we investigated the effects of varying the molecular weight of the PLA matrix and of two different mixing processes on the blend morphology and, further, on droplet coalescence during shearing. The rheological properties of these blends were investigated and the interfacial properties were analyzed using the Palierne emulsion model. Droplet coalescence was investigated by applying shear flows of 0.05 and 0.20 s−1 at a fixed strain of 60. Subsequently, small amplitude oscillatory shear tests were conducted to investigate changes in the viscoelastic properties. The morphology of the blends was also exam...

This study aims at understanding the rheological and morphological behavior of polypropylene (PP) and ethylene octene copolymer (EC) blends containing nanosilica. Maleic anhydride grafted species of PP and EC were also used to favor the localization of the silica particles in the matrix or in the dispersed phase, respectively. The morphological stability of the blends under flow was investigated by shearing at a very low shear rate of 0.01 s −1 . The morphology of the dispersed polymer phases as well as the microstructure of the silica particles inside the nanocomposites were examined using scanning and transmission electron microscopy techniques. Considering the limited time stability of composites with high level of silica loading, the low frequency data of these systems were obtained using dynamic frequency sweep data as well as an extended set of transient creep data reflecting the long time relaxation behavior. The presence of silica particles resulted in an improved morphological stability of all nanocomposites, but the effect was more pronounced when the nanoparticles were localized in the dispersed EC phase. While shearing diminished the viscoelastic properties of the blends containing no silica particle, the sheared nanocomposites with a high concentration of nanosilica revealed enhanced levels of viscoelasticity. This was attributed to the promoted interconnection of solid particles during shearing and the formation of more extended networks as confirmed by microscopic observations.

Biocomposites based on polylactide (PLA) and cellulose nanofibers (CNFs) were prepared via a solution method. The effects of CNFs on rheological, mechanical, thermal, and optical properties of PLA were investigated. Scanning electron microscopy showed that the CNFs were fairly dispersed/distributed in the PLA. Significant increases in the rheological properties of PLA/CNF composites and a remarkable shear-thinning behavior were observed. Also, apparent yield stress and a transition from liquid- to solid-like behavior indicated a strong 3D network of CNFs. At room temperature, the storage and Young moduli were increased by 50% for the composite containing 5 wt% CNFs as compared to the neat PLA, whereas the tensile strength was increased up to 31%. The Krenchel model was shown to predict well the Young modulus for lower concentrations of CNFs. Moreover, relative to the neat PLA the storage modulus in flexion at 70°C increased by 264% for PLA containing 5 wt% CNFs. Increased crystalline content and a positive shift of the crystallization temperature by incorporating the CNFs in PLA were observed. Also, good light transparency was retained for these PLA/CNF biocomposites. These results show that the preparation method employed in this work leads to PLA/CNF composites with considerably enhanced properties. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers