Polymer nanocomposites with organoclay fillers offer improved properties and performance, providing opportunities for commercial applications. The key to significant property enhancement is to exfoliate the individual organoclay platelets into the polymer matrix to utilize their high aspect ratio and modulus. The affinity between the polymer matrix and the organoclay is one of the most important factors for determining the exfoliation level. Although polar polymers, such as nylon 6, exfoliate the organoclay well, hydrophobic matrices, such as polyolefins, generally do not effectively exfoliate the organoclay. Thus, a significant part of this work investigates various routes to improve polyolefin-organoclay interactions and organoclay exfoliation in these systems. Nanocomposites formed from organoclay and blends of high density polyethylene and maleic anhydride-grafted high density polyethylene over the entire range of compositions were melt processed to obtain further insights into the 'compatiblizing' role of maleated polyolefins. The organoclay particle aspect ratio was found to initially increase drastically, reach a maximum, and slightly decrease with increased maleation. As the maleation level increases, the relative modulus increases initially and then levels off at higher loadings To a certain extent, the affinity between the polymer and the organoclay can be enhanced by optimizing the organoclay structure for a given polymer matrix. A silanized organoclay was investigated to determine if reduced agglomeration, improved exfoliation, and matrix reinforcement could be achieved in a polypropylene matrix without using a more costly compatibilizer. The silanized organoclay was found to be superior to the non-silanized precursor, but did not achieve the benefits obtained with a compatibilized matrix. Ionomer matrices have also been used as a means of improving organoclay exfoliation. This study examined the effects of ion type (K⁺, Na⁺), neutralization level, and melt index on the nanocomposite morphology and properties. The Na⁺ ionomers appear to have more favorable interactions with the organoclay. Exfoliation and matrix reinforcement tend to increase with decreased melt index and with increased neutralization, except at high levels. In these cases, it is possible that the additional exfoliation results in particles with lower aspect ratios. Composite properties are highly dependent on the particle aspect ratio. Several theories were used to predict the modulus and the thermal expansion coefficient of composites based on the filler aspect ratio. Novel two-population approaches were applied to enable the modeling of nanocomposites containing organoclay tactoids and single platelets, organoclay particles and glass fibers, or organoclay and elastomer particles. The quantitative agreement between the values predicted using experimentally determined particle aspect ratios and experimental modulus and thermal expansion was vastly improved using these methods. / text

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The morphology and mechanical properties of foams made out of ethylene-α-olefin copolymers (EC) having well-characterized rheological properties were investigated. The polymers differed in the amount of comonomer contained, type of comonomer and molecular weight, resulting in variable thermal properties and different rheological responses under shear and extensional flow. All of the octene-based copolymers with comparable rheological properties had similar foam morphology. However grades with low extensional viscosity and low crystallization points resulted in poor foams. Increasing density resulted in a higher secant modulus of the foamed samples. To further investigate the effects of material properties, trimethylolpropane trimethacrylate (TMPTMA) and triallyl trimesate (TAM) coagents were used to generate a series of PP derivatives through radical mediated melt state reactive modification. Coagent modification resulted in pronounced effects in the molecular weights and viscosities of the derivatives. However, evidence of long-chain branching (LCB) was only present in TAM modified PPs. Significant increases in the crystallization temperature, heat of fusion and crystallization rate were attributed to the formation of nanoparticles, which resulted in a heterogeneous nucleation effect, both for crystallization and foaming. Generally lower viscosities, coupled by strain hardening, enhanced nucleation and increased crystallization temperatures induced by the nanoparticles resulted in foams with higher expansion ratios and smaller cells, due to higher rates of cell growth, coupled with suppressed coalescence. Nanocomposites based on isotactic PP and nanosilica (SiO2) were prepared using a co-rotating twin-screw extruder (TSE) in order to investigate foaming on a larger scale. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good nanosilica dispersion. Well-dispersed surface-modified hydrophobic SiO2 particles were effective nucleating agents for foaming, when used at loadings below 1 phr. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2013-01-29 14:46:52.042

Polymer blends is a subject of great importance for academic as well as industrial interest. The objective of this research programme is to study the miscibility of polymer blends. Polymer blends in general are of three types: amorphous-amorphous; amorphouscrystalline; and crystalline-crystalline systems. This work is concerned with crystalline-crystalline type polymer blends and is restricted to polyolefin crystalline polymers only. Firstly an outline of crystalline-crystalline polymer blends mainly concentrating on polyolefin blends has been given in an introductory chapter. This chapter presents relevant fundamentals rather than being an extensive critical review of the literatures. In the first phase of the work three polyolefins (low-density polyethylene, high-density polyethylene and linear low-density polyethylene) have been melt mixed to prepare three sets of binary blends covering the entire range of compositions. A variety of experimental techniques were used to assess the miscibility of the blends prepared. The whole experimental programme can be subdivided into three major areas: the first is concerned with structural characterisation; the second area with the melt properties; and the third with the mechanical properties of the polymers in the solid state. Polymers (including their blends) and experimental techniques are detailed in Chapter 2. Experimental results are discussed and concluded individually in four subsequent chapters. Chapter 3 gives mainly the information of molecular structure of the three polyolefins. Characterisation of crystalline structure of polyolefins and their mixtures has been covered in Chapter 4. Chapter 5 is concerned with melt properties of polyolefins and their blends; whereas Chapter 6 deals with solid state mechanical properties. In these last two chapters an attempt has been made to correlate, where possible, the structures with their properties. From the experimental investigations it has been found that the system of linear low-density and high-density polyethylene blends is miscible whereas the system of low-density and high-density polyethylene is not. Structural characterisation has shown that the low-density and linear low-density polyethylene blends system is immiscible at all compositions, although some mechanical,compatibility has been found from melt property and mechanical property measurements. The second phase of the work was mainly concerned with the application of polyolefin blends. Film has been manufactured from polyolefin blends (including their components) and evaluated. Linear low density/ high-density and low-density/linear low-density polyethylene systems have been selected for this part of the work (Chapter 7). Essential to the understanding of the blends involving linear low-density polyethylene, is appreciation of the molecular structure of the homopolymer. A preliminary characterisation of linear lowdensity polyethylene has revealed that its structure is more complex than might have been foreseen. Finally in Chapter 8 overall concluding remarks have been made based on the conclusions drawn from all investigations carried out in this research programme and reported in the individual chapters.

The morphology and mechanical properties of foams made out of ethylene-α-olefin copolymers (EC) having well-characterized rheological properties were investigated. The polymers differed in the amount of comonomer contained, type of comonomer and molecular weight, resulting in variable thermal properties and different rheological responses under shear and extensional flow. All of the octene-based copolymers with comparable rheological properties had similar foam morphology. However grades with low extensional viscosity and low crystallization points resulted in poor foams. Increasing density resulted in a higher secant modulus of the foamed samples. To further investigate the effects of material properties, trimethylolpropane trimethacrylate (TMPTMA) and triallyl trimesate (TAM) coagents were used to generate a series of PP derivatives through radical mediated melt state reactive modification. Coagent modification resulted in pronounced effects in the molecular weights and viscosities of the derivatives. However, evidence of long-chain branching (LCB) was only present in TAM modified PPs. Significant increases in the crystallization temperature, heat of fusion and crystallization rate were attributed to the formation of nanoparticles, which resulted in a heterogeneous nucleation effect, both for crystallization and foaming. Generally lower viscosities, coupled by strain hardening, enhanced nucleation and increased crystallization temperatures induced by the nanoparticles resulted in foams with higher expansion ratios and smaller cells, due to higher rates of cell growth, coupled with suppressed coalescence. Nanocomposites based on isotactic PP and nanosilica (SiO2) were prepared using a co-rotating twin-screw extruder (TSE) in order to investigate foaming on a larger scale. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good nanosilica dispersion. Well-dispersed surface-modified hydrophobic SiO2 particles were effective nucleating agents for foaming, when used at loadings below 1 phr. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2013-01-02 11:11:07.767

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