This research provides a new insight on various properties, such as rheological, mechanical, and flame-retarding properties, as well as the foaming behaviors of wood flour /plastic composites (WPCs) through the addition of a small amount of nanosized clay particles. Although WPCs have replaced natural wood in many applications, their industrial usage has been limited because of their weak modulus, low impact strength, low screwing-ability/nailing-ability, high density compared to natural wood, as well as their flammability compared to plastics. In this context, the incorporation of nanoclay and foam structure into WPC has been studied to dramatically alleviate these drawbacks. The melt blending method was used to prepare different types of clay-filled wood flour composites such as intercalated and exfoliated clay nanocomposites. The effects of key processing variables such as the mixing time, mixing temperature and screw speed on clay dispersion were investigated from the thermodynamic and kinetic point of view. Their nanostructure was determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Accordingly, effective strategies for controlling intercalation and exfoliation of polyolefin/clay nanocomposites were proposed and evaluated. Wood flour composites with high levels of clay dispersion were synthesized successfully using a general new route (i.e., maleated-polyolefin-based clay masterbatch and dilution). The effects of nanoclay particles on the rheological, thermal, and mechanical properties were identified. In addition, it was demonstrated that a small amount of well-dispersed nanoclay in WPC significantly improved flame retardancy of WPCs. The mechanism of improved flame-retarding effects on nanoparticles was elucidated as well. The relationship between the clay dispersion and the material properties were also clarified. Furthermore, the foaming behaviors of HDPE-based and PP-based wood flour/nanoclay composites were investigated using N2 as the blowing agent in an extrusion process. The cell nucleation and growth behaviors of wood flour/polyolefin/clay composite foams were elucidated while varying the temperature, pressure, wood flour content, clay content and dispersion degrees.

This research provides a new insight on various properties, such as rheological, mechanical, and flame-retarding properties, as well as the foaming behaviors of wood flour /plastic composites (WPCs) through the addition of a small amount of nanosized clay particles. Although WPCs have replaced natural wood in many applications, their industrial usage has been limited because of their weak modulus, low impact strength, low screwing-ability/nailing-ability, high density compared to natural wood, as well as their flammability compared to plastics. In this context, the incorporation of nanoclay and foam structure into WPC has been studied to dramatically alleviate these drawbacks. The melt blending method was used to prepare different types of clay-filled wood flour composites such as intercalated and exfoliated clay nanocomposites. The effects of key processing variables such as the mixing time, mixing temperature and screw speed on clay dispersion were investigated from the thermodynamic and kinetic point of view. Their nanostructure was determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Accordingly, effective strategies for controlling intercalation and exfoliation of polyolefin/clay nanocomposites were proposed and evaluated. Wood flour composites with high levels of clay dispersion were synthesized successfully using a general new route (i.e., maleated-polyolefin-based clay masterbatch and dilution). The effects of nanoclay particles on the rheological, thermal, and mechanical properties were identified. In addition, it was demonstrated that a small amount of well-dispersed nanoclay in WPC significantly improved flame retardancy of WPCs. The mechanism of improved flame-retarding effects on nanoparticles was elucidated as well. The relationship between the clay dispersion and the material properties were also clarified. Furthermore, the foaming behaviors of HDPE-based and PP-based wood flour/nanoclay composites were investigated using N2 as the blowing agent in an extrusion process. The cell nucleation and growth behaviors of wood flour/polyolefin/clay composite foams were elucidated while varying the temperature, pressure, wood flour content, clay content and dispersion degrees.

Piezoresistivity in conductive polymer nanocomposites occurs because of the disturbance of particle networks in the polymer matrix. The piezoresistance effect becomes more prominent if the matrix material is compliant making these materials attractive for applications that require flexible force and displacement sensors such as e-textiles and biomechanical measurement devices. However, the exact mechanisms of piezoresistivity including the relationship between the matrix polymer, conductive particle, internal structure and the composite’s piezoresistance need to be better understood before it can be applied for such applications. The objective of this thesis is to report on the development of conductive polymer nanocomposites for use as flexible sensors and electrodes. Electrically conductive and piezoresistive nanocomposites were fabricated by a scalable melt compounding process. Particular attention was given to elucidating the role of matrix and filler materials, plastic deformation and porosity on the electrical conduction and piezoresistance. These effects were parametrically investigated through characterizing the morphology, electrical properties, rheological properties, and piezoresistivity of the polymer nanocomposites. The electrical and rheological behavior of the nanocomposites was modeled by the percolation-power law. Furthermore, a model was developed to describe the piezoresistance behavior during plastic deformation in relation to the stress and filler concentration.

Traditional blowing agents (e.g., hydrochlorofluorocarbons) in plastic foaming processes has been phasing out due to environmental regulations. Plastic foaming industry is forced to employ greener alternatives (e.g., carbon dioxide, nitrogen), but their foaming processes are technologically challenging. Moreover, to improve the competitiveness of the foaming industry, it is imperative to develop a new generation of value-added plastic foams with cell structures that can be tailored to different applications. In this context, the objective of this thesis is to achieve a thorough understanding on cell nucleation and growth phenomena that determine cell structures in plastic foaming processes. The core research strategy is to develop innovative visualization systems to capture and study these phenomena. A system with accurate heating and cooling control has been developed to observe and study crystallization-induced foaming behaviors of polymers under static conditions. The cell nucleation and initial growth behavior of polymers blown with different blowing agents (nitrogen, argon and helium, and carbon dioxide-nitrogen mixtures) have also been investigated in great detail. Furthermore, two innovative systems have been developed to simulate the dynamic conditions in industrial foaming processes: one system captures a foaming process under an easily adjustable and uniform extensional strain in a high temperature and pressure environment, while the other achieves the same target, but with shear strain. Using these systems, the extensional and shear effects on bubble nucleation and initial growth processes has been investigated independently in an isolated manner, which has never been achieved previously. The effectiveness of cell nucleating agents has also been evaluated under dynamic conditions, which have led to the identification of new foaming mechanisms based on polymer-chain alignment and generation of microvoids under stress. Knowledge generated from these researches and the wide range of future studies made possible by the visualization systems will be valuable to the development of innovative plastic foaming technologies and foams.

Starch-derived bioplastics are an inexpensive, renewable and environmentally-friendly alternative to traditional petroleum-based plastics. Proteins secreted by Ophiostoma ulmi, were investigated for their application in bioplastic product. Proteins were isolated from fungal cultures by anion exchange chromatography and used to treat starch. Subsequently, plastic films were generated by solution casting, with glycerol as plasticizer. Tensile strength of the films was found to increase significantly compared to the control. The relative water holding capacity of the treated starch also decreased dramatically. Attempts to identify fungal proteins by MALDI-TOF MS/MS did not result in positive matches, mainly due to lack of fungal sequence information. Additionally, the effect of non-specific proteins resulted in a modest increase in tensile strength and a slightly greater effect on water absorption. Proteins secreted by O. ulmi were therefore implicated in improving properties of starch-based plastics. Investigation into the role of an extracellular polysaccharide is also suggested.

Starch-derived bioplastics are an inexpensive, renewable and environmentally-friendly alternative to traditional petroleum-based plastics. Proteins secreted by Ophiostoma ulmi, were investigated for their application in bioplastic product. Proteins were isolated from fungal cultures by anion exchange chromatography and used to treat starch. Subsequently, plastic films were generated by solution casting, with glycerol as plasticizer. Tensile strength of the films was found to increase significantly compared to the control. The relative water holding capacity of the treated starch also decreased dramatically. Attempts to identify fungal proteins by MALDI-TOF MS/MS did not result in positive matches, mainly due to lack of fungal sequence information. Additionally, the effect of non-specific proteins resulted in a modest increase in tensile strength and a slightly greater effect on water absorption. Proteins secreted by O. ulmi were therefore implicated in improving properties of starch-based plastics. Investigation into the role of an extracellular polysaccharide is also suggested.

Traditional blowing agents (e.g., hydrochlorofluorocarbons) in plastic foaming processes has been phasing out due to environmental regulations. Plastic foaming industry is forced to employ greener alternatives (e.g., carbon dioxide, nitrogen), but their foaming processes are technologically challenging. Moreover, to improve the competitiveness of the foaming industry, it is imperative to develop a new generation of value-added plastic foams with cell structures that can be tailored to different applications. In this context, the objective of this thesis is to achieve a thorough understanding on cell nucleation and growth phenomena that determine cell structures in plastic foaming processes. The core research strategy is to develop innovative visualization systems to capture and study these phenomena. A system with accurate heating and cooling control has been developed to observe and study crystallization-induced foaming behaviors of polymers under static conditions. The cell nucleation and initial growth behavior of polymers blown with different blowing agents (nitrogen, argon and helium, and carbon dioxide-nitrogen mixtures) have also been investigated in great detail. Furthermore, two innovative systems have been developed to simulate the dynamic conditions in industrial foaming processes: one system captures a foaming process under an easily adjustable and uniform extensional strain in a high temperature and pressure environment, while the other achieves the same target, but with shear strain. Using these systems, the extensional and shear effects on bubble nucleation and initial growth processes has been investigated independently in an isolated manner, which has never been achieved previously. The effectiveness of cell nucleating agents has also been evaluated under dynamic conditions, which have led to the identification of new foaming mechanisms based on polymer-chain alignment and generation of microvoids under stress. Knowledge generated from these researches and the wide range of future studies made possible by the visualization systems will be valuable to the development of innovative plastic foaming technologies and foams.

In this thesis, I describe experiments that were designed to provide a better understanding of polymer diffusion during latex film formation. This step leads to the improvement of film mechanical properties. Polymer diffusion in these films was monitored by fluorescence resonance energy transfer. Current paint formulations contain Volatile Organic Compounds (VOCs) as plasticizers to facilitate polymer diffusion. The drawback of this technology is the release of VOCs to the atmosphere. VOCs are deleterious to the environment and contribute to smog and ground level ozone formation. The propensity of water, an indispensible part of any latex dispersion, to promote polymer diffusion was studied. Copolymers of poly (butyl acrylate-co-methyl methacrylate) and poly(ethylhexyl acrylate-co-tertiary butyl methacrylate) with similar glass transition temperatures but different hydrophobicity were compared. Polymer diffusion was monitored for films aged at different relative humidities. Water absorbed by the hydrophobic copolymer film was less efficient in promoting polymer diffusion than in the hydrophilic polymer. Only the fraction of water which is molecularly dissolved in the film participate actively in plasticization. Although water has low solubility in most latex polymers, molecularly dissolved water is more efficient than many traditional plasticizers. The possibility of modifying film formation behavior of acrylic dispersions with oligomers was studied by synthesizing hybrid polymer particles consisting of a high molecular weigh (high-M) polymer and an oligomer with the same composition. Oligomers with lower molecular weight are more efficient as diffusion promoters and have less deleterious effect on high-M polymer viscosity. A different set of hybrid particles were prepared in which the oligomer contained methacrylic acid units. The composition of the oligomer was tuned to be miscible with the high-M polymer when the acid groups were protonated but to phase separate when the acid groups were deprotonated. At basic pH, these particles adopt a core-shell morphology, with a shell rich in neutralized oligomers. After film formation, the oligomer shell retarded polymer diffusion. This retardation is expected to expand the time window during which the paint surface can be altered without leaving brush marks (open time). Short open time is a pressing problem in current technology.

In this thesis, I describe experiments that were designed to provide a better understanding of polymer diffusion during latex film formation. This step leads to the improvement of film mechanical properties. Polymer diffusion in these films was monitored by fluorescence resonance energy transfer. Current paint formulations contain Volatile Organic Compounds (VOCs) as plasticizers to facilitate polymer diffusion. The drawback of this technology is the release of VOCs to the atmosphere. VOCs are deleterious to the environment and contribute to smog and ground level ozone formation. The propensity of water, an indispensible part of any latex dispersion, to promote polymer diffusion was studied. Copolymers of poly (butyl acrylate-co-methyl methacrylate) and poly(ethylhexyl acrylate-co-tertiary butyl methacrylate) with similar glass transition temperatures but different hydrophobicity were compared. Polymer diffusion was monitored for films aged at different relative humidities. Water absorbed by the hydrophobic copolymer film was less efficient in promoting polymer diffusion than in the hydrophilic polymer. Only the fraction of water which is molecularly dissolved in the film participate actively in plasticization. Although water has low solubility in most latex polymers, molecularly dissolved water is more efficient than many traditional plasticizers. The possibility of modifying film formation behavior of acrylic dispersions with oligomers was studied by synthesizing hybrid polymer particles consisting of a high molecular weigh (high-M) polymer and an oligomer with the same composition. Oligomers with lower molecular weight are more efficient as diffusion promoters and have less deleterious effect on high-M polymer viscosity. A different set of hybrid particles were prepared in which the oligomer contained methacrylic acid units. The composition of the oligomer was tuned to be miscible with the high-M polymer when the acid groups were protonated but to phase separate when the acid groups were deprotonated. At basic pH, these particles adopt a core-shell morphology, with a shell rich in neutralized oligomers. After film formation, the oligomer shell retarded polymer diffusion. This retardation is expected to expand the time window during which the paint surface can be altered without leaving brush marks (open time). Short open time is a pressing problem in current technology.