Effect of processing conditions on morphology and mechanical properties of compatibilized polypropylene nanocomposites

Evolution of the Microstructure of PP-LDHs Nanocomposites during Melt Compounding: A Simulation Approach

In the context of polymer-based nanocomposites containing layered nanofillers, the achievement of good extents of dispersion and distribution of the embedded nanoparticles and, even more, the obtainment of intercalated and/or exfoliated structures through melt compounding still represents a persistent challenge, especially in the case of anionic layered double hydroxides (LDHs)-containing systems and non-polar polymeric matrices. In this work, a simulation approach is proposed to evaluate the influence of the processing conditions on the morphology of polypropylene (PP)-based nanocomposites containing organomodified LDHs. In particular, the effect of the screw rotation speed and the feed rate on the final microstructure of the materials formulated through melt compounding in a twin-screw extruder was assessed. The rheological and morphological characterizations demonstrated that a more homogeneous morphology was achieved when high levels of both exploited processing parameters are selected. The results coming from the simulation of the processing were used to establish some relationships between the flow parameters and the microstructure of the nanocomposites, demonstrating that low residence times coupled with high local shear rates are required to ensure the achievement of homogenous morphologies, likely involving the occurrence of intercalation phenomena.

Mechanical, rheological and thermal properties of montmorillonite-modified polyhydroxybutyrate composites

Polyhydroxybutyrate (PHB), a bio-derived and biodegradable polyester, has the potential to be a substitute for traditional polymers. PHB was modified with montmorillonite (MMT), a nanoclay, with the aim of improving its mechanical properties. The clay dispersion, mechanical, rheological and thermal properties of untreated and acid-treated MMT-modified PHB nanocomposites were investigated. Nanocomposite specimens at three different clay loading were prepared using extruder and injection moulding machine. Energy dispersive X-ray mapping revealed that nanocomposites with clay content of 3 phr exhibited better dispersion compared to nanocomposites with higher clay content. The mechanical properties of the MMT-modified PHB, such as the tensile and flexural modulus, were enhanced when compared to neat PHB. From rheology, PHB and PHB nanocomposites modified with untreated MMT exhibited Newtonian fluid behaviour in the tested frequency range. However, for nanocomposites modified with acid-treated MMT, shear thinning behaviour was observed at higher clay content. The nanocomposites also exhibited higher complex viscosity compared to PHB. From transmission electron microscopy analysis, exfoliation of the MMT was observed for the treated MMT nanocomposites at all clay loading. MMT-modified PHB has lower melting temperature when compared to neat PHB. Furthermore, it was found that the addition of MMT influenced the crystallisation behaviour of PHB. The presence of acid-treated MMT also reduced the degree of crystallinity with increasing clay content.

Influence of Different Carbon-Based Fillers on Electrical and Mechanical Properties of a PC/ABS Blend

The present work examines the influence of different carbon-based fillers on the performance of electrically conductive polymer blend composites. More specifically, we examined and compared the effects of graphene (GR), carbon nanotubes (CNTs) and carbon black (CB) on a PC/ABS matrix by morphological investigation, electrical and physic-mechanical characterization. Electrical analyses showed volume resistivity decreased when the CNTs and CB content were increased, although the use of melt-mixed GR did not really influence this property. For the latter, solution blending was found to be more suitable to obtain better GR dispersion, and it obtained electrical percolation with a graphene content ranging from 0.5% to 1% by weight, depending on the solvent removal method that was applied. There was a gradual improvement in all of the composites’ dielectric properties, in terms of loss factor, with temperature and the concentration of the filler. As expected, the use of rigid fillers increased the composite stiffness, which is reflected in a continuous increment in the composites’ modulus of elasticity. The improvements in tensile strength and modulus were coupled with a reduction in impact strength, indicating a decrease in polymer toughness and flexibility. TEM micrographs allowed us to confirm previous results from studies on filler dispersion. According to this study and the comparison of the three carbon-based fillers, CNTs are the best filler choice in terms of electrical and mechanical performance.

Influence of Processing Conditions on the Preparation of Clay-Based Nanocomposites by Twin-Screw Extrusion

This review paper is devoted to the preparation of clay-based thermoplastic nanocomposites by melt blending in a twin-screw extruder. The influence of the main processing parameters (screw speed, feed rate, barrel temperature, screw profile) on the state of the clay dispersion at the micro- and nanoscale is characterized. The change of dispersion state along the screws and the corresponding mechanisms are presented. The interest of process modelling to predict the state of dispersion is evaluated and, finally, the main modifications of the twin-screw extrusion process to improve the clay dispersion are reviewed.

Attempts to Optimize the Dispersion State during Twin-Screw Extrusion of Polypropylene/Clay Nanocomposites

Polypropylene/organoclay nanocomposites were prepared by melt-mixing in a twin-screw extruder. Polypropylene grafted with maleic anhydride was used as compatibilizer. The evolution of the microstructure along the screw profile was characterized through dead-stop experiments. In order to quantify the multi-scale dispersion state of the nanocomposites, different techniques have been used: scanning electronic microscopy (SEM) to observe the large remaining aggregates, X-Ray diffraction measurements to characterize the intercalation state by measuring the interlamellar distance, and finally rheological characterizations in the molten state to assess the dispersion state at the nanoscale. The effects of low barrel temperatures and high matrix viscosity were tested, in order to improve exfoliation by an increase in shear stresses.

Matrix Degradation during High Speed Extrusion of Polypropylene/Clay Nanocomposites – Influence on Filler Dispersion

We prepared polypropylene/organoclay nanocomposites by melt blending in a twin-screw extruder, exploring the domain of high screw speeds (up to 1 100 min−1). The samples were characterized at both microscale (size of agglomerates) and nanoscale (level of exfoliation). We show that, despite a satisfactory exfoliation, the polymer matrix suffered important thermomechanical degradation by chain scission. We propose a way to correct this degradation on the viscosity curves and we confirm that high screw speeds are not necessarily favorable to clay exfoliation, essentially because of the too high melt temperatures encountered during the process.

Influence of Melt-Mixing Process Conditions on Mechanical Performance of Organoclay/Fluoroelastomer Nanocomposites

In this study, Cloisite 20A, an organically modified Montmorillonite (Mnt), has been incorporated into Fluoroelastomer (FKM) through melt intercalation technique. Since the nanocomposite preparation method and conditions, and consequently, the resulting morphology play a critical role in the final properties, the effect of different process conditions such as time, temperature, and shear rate on the vulcanization, thermal and mechanical properties have been investigated. The morphology of nanocomposites, prepared at different melt-mixing conditions, was studied using X-ray diffraction (XRD). Rheological, thermal and mechanical behaviors were investigated by moving die rheometer (MDR), thermal gravimetric analysis (TGA), and tensile strength test respectively. Also, the crosslinking density has been measured for the nanocomposites. The best mechanical performance of clay/FKM nanocomposites was attained by optimization of the melt-mixing conditions. We achieved the following enhancements for FKM by clay incorporation: enhancement of tensile strength up to 70 %; elongation up to 94 %; and modulus up to 405 %. Process temperature was found to have a critical role in the final properties of the nanocomposites, while mixing residual time and shear rate had a moderate effect. The most desirable properties and curing behaviors, including highest maximum torques, cure rates, crosslinking densities, fast crosslinking kinetics, high intercalation and best improved tensile strengths, resulted with specific combination of melt-mixing parameters.

The impact of ultra-low amounts of amino-modified MMT on dynamics and properties of densely cross-linked cyanate ester resins

ABSTRACT

Thermostable nanocomposites based on densely cross-linked cyanate ester resins (CER), derived from bisphenol E and doped by 0.01 to 5 wt. % amino-functionalized 2D montmorillonite (MMT) nanoparticles, were synthesized and characterized using Fourier transform infrared (FTIR), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), far-infrared (Far-IR), and creep rate spectroscopy (CRS) techniques. It was revealed that ultra-low additives, e.g., 0.025 to 0.1 wt. %, of amino-MMT nanolayers covalently embedded into СER network exerted an anomalously large impact on its dynamics and properties resulting, in particular, in some suppression of dynamics, increasing the onset of glass transition temperature by 30° to 40° and twofold rise of modulus in temperature range from 20°C to 200°C. Contrarily, the effects became negligibly small or even negative at increased amino-MMT contents, especially at 2 and 5 wt. %. That could be explained by TEM/EDXS data displaying predominance of individual amino-MMT nanolayers and their thin (2 to 3 nanolayers) stacks over more thick tactoids (5 to 10 nanolayers) and the large amino-MMT aggregates (100 to 500 nm in thickness) reversing the composite structure produced with increasing of amino-MMT content within CER matrix. The revealed effect of ultra-low amino-MMT content testifies in favor of the idea about the extraordinarily enhanced long-range action of the 'constrained dynamics' effect in the case of densely cross-linked polymer networks.

PACS

82.35.Np Nanoparticles in polymers; 81.05.Qk Reinforced polymers and polymer-based composites; 81.07.Pr Organic-inorganic hybrid nanostructures.

Preparation of Polymer-Clay Nanocomposites by Melt Mixing in a Twin Screw Extruder: Using On-Line SAOS Rheometry to Assess the Level of Dispersion

A prototype on-line rotational rheometer was fixed between a twin screw extruder and a multi-rod die of an industrial pelletization line used for the manufacture of polymer-clay nanocomposites. After diverting the required amount of melt to the device, measurements were performed in small amplitude oscillatory shear and used to estimate the level of dispersion of the organoclay in the polypropylene matrix, by means of correlations that are commonly utilized. The aim is to determine whether changes in clay type, clay content, feed rate and screw speed cause detectable alterations in the rheological response and thus in the level of dispersion, with a view to practical process monitoring and control. The analysis of the data is supported by XRD and electron (scanning and transmission) microscopy observations.

Rheological and Thermal Behaviour of Different Molecular Structure Polypropylene Blends

High melt strength/block polypropylene (HMSPP/PPB) blends and high melt strength/random polypropylene (HMSPP/PPR) blends were prepared by a twin-screw extruder to decrease the high stiffness of polypropylene and to improve its impact strength. Rheological properties of the two blends were investigated using a rotational rheometer. The complex viscosity and storage modulus data at low frequency region indicated that the melt elasticity and melt strength of the blends were affected by varying the content of PPB and PPR in the blends. Moreover, the melt strength of HMSPP/PPR blends was better than that of HMSPP/PPB. The non-isothermal crystallization behaviour of the blends was studied using differential scanning calorimetry with various cooling rates and was analyzed by the Avrami method. It was found that the melt and crystallization temperatures of the blends increased with the ratio of PPR and PPB. PPB also changed the crystallization process of the blends, leading to smaller spherulite size and more spherulites, but PPR only slightly affected the crystal behaviour.

Structural and Rheological Properties as a Function of Mixing Energy for Polymer/Layered Silicate Nanocomposites

Polyamide/organoclay nanocomposites have been prepared via direct melt intercalation in an internal mixer at 2.5% volume fraction, under various processing conditions. The influence of the melt mixing conditions on the structure and on the oscillatory and steady shear rheological properties of PA-12 layered silicate nanocomposites has been studied. Both structural properties and melt state material properties of nanocomposites were shown to exhibit similar trends when studied as a function of the specific mixing energy. Low frequency storage and loss moduli, but also yield stress and low-shear first normal stress difference were shown to increase up to a critical value of this specific mixing energy, and to level off above this value.

Effect of Processing Conditions on Properties of PET/Clay Nanocomposite Films

Polyethylene terephthalate (PET) nanocomposite films (with 3 wt.% Cloisite 30B) were prepared by cast extrusion followed by uniaxial stretching, using chill rolls. Two screw profiles with different mixing elements under different screw speeds (N) and feeding rates (Q) were used to prepare PET/clay nanocomposite (PCN) films. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) showed that the clay layers were aligned in the machine direction (MD). XRD patterns depicted that the interlayer distance of clay platelets in the state of intercalation is somehow independent of the processing conditions, but the macro-scale characterization, including barrier and mechanical properties, showed that the level of clay layer delamination was affected by processing conditions. The results reveal that the applied strain has stronger effect than residence time on the barrier and mechanical properties. At the highest screw speed (N = 250 min−1), 27% reduction in oxygen permeability and 30% improvement in tensile modulus were obtained for the more severe screw profile.

Influence of Twin-Screw Processing Conditions on Structure and Properties of Polypropylene – Organoclay Nanocomposites

This study looks at the influence of extrusion parameters such as screw speed, feed rate and barrel temperature on the nanocomposite structure (size of agglomerates, level of intercalation and exfoliation) and its consequences on final mechanical properties. Nanocomposites of polypropylene, maleated polypropylene and organomodified montmorillonite, with respective mass fractions of 85/10/5, were prepared in a co-rotating twin-screw extruder using a masterbatch dilution method. The nanocomposites structure was quantified by scanning and transmission electron microscopy, X-ray diffraction and dynamic rheometry. Relationships between the microstructure at different levels (size and number of agglomerates, interlayer distance, melt yield stress to quantify the exfoliation level) and the processing conditions were established, revealing that specific mechanical energy received during extrusion was the key parameter controlling this microstructure. Mechanical properties in uniaxial tension (apparent Young's modulus) were measured and related to the microstructural parameters resulting from extrusion conditions.