Morphology and properties of polypropylene nanocomposites based on a silanized organoclay

Obtaining the Dimensions and Orientation of 2D Rectangular Flakes from Sectioning Experiments in Flake Composites

Recently, we developed and reported the statistical validity of two methods for determining the planar aspect ratios of two-dimensional (2D) rectangular flakes in composites from the statistics of intersection lengths: one method is based on the maximum intersection length, and the other on the average intersection length. In this work, we show that these methods are valid and robust not only for flakes having isotropic, random in-plane orientations, but for the more general situations of planar orientations ranging from unidirectional (misalignment angle ϵ=0), to partially aligned (0<ϵ<π/2), to flakes of isotropic, random-in-plane orientations (ϵ=π/2). We prove, by Monte Carlo simulations and by numerical sectioning experiments, the validity of the proposed methods for characterizing the extent of the partial alignment (the misalignment angle ϵ) of 2D rectangular flakes in composites, based again on the statistics of the intersection lengths; this information can be obtained from cross-sections of composite samples used in optical or electron microscopy or using tomographic imaging techniques. The performance of these techniques was tested using blind experiments in numerically sectioned composites which contained up to 106 individual flakes, and was found to be very good for a wide range of flake aspect ratios.

A Novel Method for the Determination of the Lateral Dimensions of 2D Rectangular Flakes

We present a novel method for the determination of the lateral dimensions of thin rectangular flakes, as they exist randomly dispersed in flake composites. Knowledge of flake size and shape is essential for the correct prediction of the mechanical, electrical, thermal and barrier properties of flake composites. The required information is the distribution function of lengths of the lines representing the intersection of flakes with a sectioning plane, as seen in cross-sections of composite samples used in optical or electron microscopy or obtained using tomographic imaging techniques. The key observation is that the major peak of the distribution function coincides with the short dimension S of the flake while a secondary peak corresponds to its long dimension W. These observations are explained using Monte-Carlo simulations, as well as deterministic, geometry-based modeling and probability analysis. Since the strength of the secondary peak diminishes with increasing flake aspect ratio r=W/S, we develop two additional methods for the determination of W. The first finds W from the maximum intersection length; this procedure is justified by computing the relevant probability fields through Monte-Carlo simulations. The second method finds r from the average intersection length and is valid in the range 1<r<15. The performance of these techniques is tested and found to be very good using blind experiments in numerically sectioned specimens.

Effect of Basalt Powder Surface Treatments on Mechanical and Processing Properties of Polylactide-Based Composites

Legislative restrictions and the needs of consumers have created a demand for sustainable materials. Polylactide (PLA) is a biodegradable polyester with advantageous mechanical properties, however, due to its low crystallization rate, it also has low thermomechanical stability. Its range of application temperatures can be widened using nucleating agents and fillers including basalt powder (BP), a waste product from the mining industry. This study analyzed the possibility of enhancing the properties of a PLA-BP composite by chemically treating the filler. Basalt powder was subjected to silanization with 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane and mixed with PLA at 5-20 wt%. The nucleating effect of a potassium salt of 3,5-bis(methoxycarbonyl) (LAK-301) in the silanized composite was also evaluated. The properties of the materials with silanized BP were compared with the unmodified basalt powder. The miscibility of the filler and the polymer was assessed by oscillatory rheometry. The structure of the composites was studied using scanning electron microscopy and their thermomechanical properties were analyzed using dynamic mechanical thermal analysis. Mechanical properties such as tensile strength, hardness and impact strength, and heat deflection temperature of the materials were also determined. It was concluded that BP-filled nucleated PLA composites presented satisfactory thermomechanical stability without silanization, but chemical treatment could improve the matrix-filler interactions.

Structural Nanocomposite Fabrication from Self-Assembled Choline Chloride Modified Kaolinite into Poly(Methylmethacrylate)

Composite materials produced from indigenous nanoscale particles and synthetic polymers have created demand in the field of nanoscience and technology. Layered silicates are potential candidates for reinforcing the properties of composites. Here, we report the fabrication of nanocomposites using poly(methylmethacrylate) (PMMA) as the matrix and the Bijoypur clay of Bangladesh known as kaolinite (200–250 nm) as the filler via solution casting. Kaolinite was first modified using choline chloride to prepare core-shell particles through a precipitation technique and was used for self-assembled nanocomposite films preparation. A series of nanocomposites films using 0, 1, 3, 5 and 10% (w/w) modified kaolinite was prepared. The neat PMMA and nanocomposite films were characterized by attenuated total reflection infra-red (ATR-IR) spectroscopy and X-ray diffraction (XRD) techniques. The mechanical properties, thermal stability, and morphology of the films were investigated using a universal testing machine (UTM), a thermal gravimetric analyzer (TGA), and a scanning electron microscope (SEM). The nanocomposite films exhibited better mechanical properties and thermal stability than neat PMMA film. Development of such structural nanocomposite materials using naturally occurring nanoscale particles would play a crucial role in the field of materials science for packaging applications and separation technology.

Compatibilizer Polarity Parameters as Tools for Predicting Organoclay Dispersion in Polyolefin Nanocomposites

Nanocomposites give an innovative method to increase the mechanical, thermal, and barrier performance of polymers. However, properly dispersing the nanoparticles in the polymer matrix is often key in achieving high performance, especially in the case of hydrophilic nanoparticles and hydrophobic polymers. For that purpose, nanoparticles may be functionalized with organic groups to increase their affinity with the polymer matrix. Compatibilizing agents may also be included in the nanocomposite formulation. This paper aims at identifying parameters relative to the compatibilizer polarity that would allow predicting nanoparticle dispersion in the polymer nanocomposite. The analysis used published data on nanocomposite samples combining clay nanoparticles, polyolefins, and various compatibilizing agents. We studied the correlations between the nanoclay exfoliation ratio and five different parameters describing the compatibilizer hydrophilic-lipophilic balance: the acid value, the mole, and weight fraction of polar groups, the number of polymer chain units per polar group, and the number of moles of polar groups per mole of compatibilizer. The best correlation was observed with the number of polymer chain units per polar group in the compatibilizer. This parameter could be used as a tool to predict the dispersion of organoclay nanoparticles in polyolefins. Another important result of the study is that, among the compatibilizers investigated, those with a low acid value provided a better nanoclay exfoliation compared to those with a high acid value. This may indicate the existence of a maximum in the nanoclay exfoliation/compatibilizer polarity curve, which would open new perspectives for nanocomposite performance optimization.

Processing of Polypropylene-Organic Montmorillonite Nanocomposite by Equal Channel Multiangular Extrusion

By the example of polypropylene-organic montmorillonite composite (PP-OMMT), the abilities of the method of equal channel multiangular extrusion have been studied with respect to the modification of the structure and the properties of polymeric nanocomposites. With using X-ray structure analysis, TEM, DSC, and dilatometry, it has been demonstrated that this kind of processing provides an additional intercalation of the polymer into OMMT tactoids with the succeeding exfoliation and facilitates an increase in the aspect ratio, the degree of platelet orientation, the crystalline lamellar thickness, and a decrease in the dispersion of the crystallite thickness, as well as the formation of biaxial orientation of the OMMT and PP crystals. The observed structure rearrangements determine enhanced microhardness, ductility, and the heat distortion temperature of the PP-OMMT composite.

Hierarchical structures of olefinic blocky copolymer/montmorillonite nanocomposites with collapsed and intercalated clay layers

Hierarchical structures of two types of nanocomposite at different scales were characterized by various techniques.