Fabrication and characterization of carbon nanotube-reinforced polypropylene matrix composites

Carbon nanotube reinforced polymer composites have recently been the focus of numerous research efforts. With regards to mechanical behavior, the enhancements reported are much lower than the theoretical predictions. One of the main challenges being tackled is achieving a uniform dispersion. Solvent mixing has been used extensively. Concerns, however, arose that unevaported solvents could negatively affect the mechanical properties. In this thesis, solvent and dry mixing for dispersing MWNT powders within the polymer prior to fabrication by melt processing are compared. Various weight fractions of CNT are added and the effect on the mechanical, crystallization and flow properties of the resulting composites is investigated. In both cases, enhancements in yield strength compared to the neat polymer were observed. It was found that dry mixing produced composites with the highest yield strength at 0.5 wt % CNT, whereas solvent mixing produced a similar enhancement at CNT contents of 1 wt %. It is believed that this difference is primarily dependent on the dispersion of CNTs within the polymer matrix. On the other hand, ductility was much higher for solvent mixed samples compared to dry mixed ones. FESEM analysis showed the presence of clusters in large wt % CNT samples produced by dry mixing. All samples produced by solvent mixing were found to contain homogeneously distributed CNTs. In most cases, CNT pull-out was found to be the dominant failure mechanism and may explain the limited enhancement observed. Further mechanical characterization was done using nanoindentation. The hardness and indentation modulus were calculated and they appear to concur with the tension test results. The crystallinity of the polypropylene matrix was also investigated before and after the addition of the CNTs. It was found that adding the lowest CNT wt% led to an increase in the crystallization temperature. A gradual increase in the crystallization temperature occurred with the addition of higher CNT loadings. This indicated that the CNTs acted as nucleating agents for the polypropylene crystals. In the plastics industry the flow properties of the polymer is very important. Melt flow index measurements were used in this study to analyze this property. A decreasing trend in the melt flow index i.e. increasing viscosity was found for the solvent- mixed samples which have superior dispersion expected to contribute to decreasing the viscosity of the molten polymer. However, the effect of the addition of the CNTs overcame this and resulted in the increase of the viscosity. This occurrence could be due to the dispersion process of solvent mixing preceding the shear mixing stage. Another indication for the poor dispersion of CNT in the dry-mixed samples was that the decrease in the melt flow index of the produced samples is very limited if not negligible

Preparing, Characterizing, On-Line Digital Image Processing of Residence Time Distribution and Modeling of Mechanical Properties of Nanocomposite Foams

The objectives of this research were to prepare, characterize and to study the effects of organoclay and extrusion variables on the physical, mechanical, structural, thermal and functional properties of tapioca starch (TS)/poly(lactic acid) (PLA) nanocomposite foams. On-line digital imaging processing was used to determine residence time distribution (RTD). Adaptive neuro-fuzzy inference system (ANFIS) was used to model the mechanical properties of nanocomposite foams. Four different organoclays (Cloisite 10A, 25A, 93A, 15A) were used to produce nanocomposite foams by melt-intercalation. The properties were characterized using Xray diffraction, scanning electron microscopy, differential scanning calorimetric, and Instron universal testing machine. The properties were influenced significantly with the addition of different organoclays. TS/PLA/Cloisite 30B nanocomposite foams, with four clay contents of 1, 3, 5, 7 wt%, were prepared by a melt-intercalation method. Among the four nanocomposites, 3 wt% clay content produced significantly different properties. Screw speed, screw configuration, die nozzle diameter and moisture content were varied to determine their effects on organoclay intercalation. These extrusion variables had significant effects on the properties of TS/PLA /Cloisite 10A nanocomposite foams due to the intercalation of organoclay. Multiple inputs single output (MISO) models were developed to predict mechanical properties of nanocomposite foams. Four individual ANFIS models were developed. All models preformed well with R2 values \u3e 0.71 and had very low root mean squared errors (RMSE). Effects of screw configurations and barrel temperatures on the RTD and MISO models were developed to predict mechanical properties. The influence of the extrusion variables had a significant effect on the mean residence time (MTR). On-line digital image processing (DIP) technique was developed to measure the RTD as compared to the colorimeter method. R2 showed a correlation of 0.88 of a* values from both methods. The influence of screw configuration and temperature on RTD were analyzed by the MRT and variance for both methods. Mixing screws and lower temperature resulted in higher MRT and variance for both methods

Lightweight Metal Based Composites

Ph.DDOCTOR OF PHILOSOPH

Microstructure and mechanical properties of aluminium based nanocomposites strengthened with alumina and silicon carbide

Al-Al₂O₃ and Al-4wt%Cu-SiC metal matrix nanocomposites were studied because these materials have a potential for offering good ductility, high strength, and high electrical and/or thermal conductivity, which make them ideal for engineering applications such as aerospace and automobile components. In order to achieve these goals the reinforcement phase needs to be in a particulate form, and the size of the particles needs to be small. Samples of aluminium based nanocomposites were produced with different volume fractions, ranging from 2.5-10 vol.% of alumina (Al₂O₃) and silicon carbide (SiC) nanoparticles. High energy mechanical milling (HEMM) with various milling times ranging from 6-12 hours was used to produce these samples. Optical microscopy, XRD, SEM, TEM and microindentation were used to characterize the milled powder and bulk samples. Bulk solid Al-(2.5-10) vol. % Al₂O₃ and Al-4wt%Cu-(2.5-10) vol. %SiC nanocomposites samples were produced using different powder consolidation techniques such as powder compact forging and powder compact extrusion. The microstructure of the composite powder/balls/granules produced was studied in details to understand the morphology, macrostructure and microstructural evolution during the HEMM and with changing volume percent of the reinforcements in the matrix. The nano SiC and Al₂O₃ were imbedded into the aluminium matrix due to the high forces and strains affecting particle surfaces during milling and the very small size of the reinforcement relative to the size of the Al particles. The average microhardness was increased with increasing volume fraction of reinforcement within the matrix. HEMM was used to fabricate Ultra-Fine Grained (UFG) and nanostructured Al- (2.5-10) vol. %Al₂O₃ composites with a dispersion of nano alumina within the matrix and Al-4wt%Cu- (2.5-10) vol%SiC with two different sizes of SiC in the micro and nano ranges. A UFG structure in the Al and Al-(2.5-10)vol.% Al₂O₃ nanocomposites can be synthesized by a combination of high energy mechanical milling and severe plastic deformation used to consolidate the powder compacts into nearly fully dense forged discs and extruded bars. No significant microscopic yielding was found in the Al-2.5 and 10 vol. %Al₂O₃ composites produced by powder compact forging. However, Al-5vol. % Al₂O₃ showed plastic yielding of 8%, and the best fracture strength of 343 MPa. No significant microscopic yielding was noticed for the Al- 10 vol. %Al₂O₃ composite produced by powder compact extrusion. Al-2.5vol. % Al₂O₃ showed plastic yielding of ~1% with the highest tensile strength of 364 MPa while Al-5vol. % Al₂O₃ showed plastic yielding of 8% with a yield strength of 318 MPa. The average microhardness of the extruded bars for Al-4wt%Cu-(2.5-10)vol.% SiC increased from 104 HV to 205 HV with increasing the volume fraction of SiC nanoparticles from 2.5 to 10%. The ultimate tensile strength increased from 168 MPa to 400 MPa with increasing volume fraction of SiC nanoparticles from 2.5 to 5% while the ductility dropped from 6.8% to 1.2 %. The fracture strength of the Al-4wt%Cu-micro-SiC was increased from 225 MPa for Al-4wt%Cu-2.5vol. %SiC to 412 MPa for Al-4wt%Cu-10vol. % SiC. The Al-4wt%Cu-2.5vol. %SiC forged disc did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol. %SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%)

Developing of Ultrasound Experimental Methods using Machine Learning Algorithms for Application of Temperature Monitoring of Nano-Bio-Composites Extrusion

In industry fiber degradation during processing of biocomposite in the extruder is a problem that requires a reliable solution to save time and money wasted on producing damaged material. In this thesis, We try to focus on a practical solution that can monitor the change in temperature that causes fiber degradation and material damage to stop it when it occurs. Ultrasound can be used to detect the temperature change inside the material during the process of material extrusion. A monitoring approach for the extruder process has been developed using ultrasound system and the techniques of machine learning algorithms. A measurement cell was built to form a dataset of ultrasound signals at different temperatures for analysis. Machine learning algorithms were applied through machine-learning algorithm’s platform to classify the dataset based on the temperature. The dataset was classified with accuracy 97% into two categories representing over and below damage temperature (190oc) ultrasound signal. This approach could be used in industry to send an alarm or a temperature control signal when material damage is detected. Biocomposite is at the core of automotive industry material research and development concentration. Melt mixing process was used to mix biocomposite material with multi-walled carbon nanotubes (MWCNTs) for the purpose of enhancing mechanical and thermal properties of biocomposite. The resulting composite nano-bio- composite was tested via different types of thermal and mechanical tests to evaluate its performance relative to biocomposite. The developed material showed enhancement in mechanical and thermal properties that considered a high potential for applications in the future

Functional Biodegradable Nanocomposites

Concern around environmental issues facing society has grown significantly in recent years. Reduction in damages resulting from both industrial and domestic waste has become a key topic as a means to address environmental problems and the exhaustion of natural resources. Likewise, the use of materials of polymeric origin in applications such as tissue regeneration, controlled release of medicines, packaging, soil remediation, etc., makes the development of materials biodegradable in biological media increasingly important. Recently, significant progress has been achieved in the creation of biodegradable polymeric formulations with functionalities similar to those of non-biodegradable polymers, both of natural and of synthetic origin, extending their applicability to fields such as food packaging, electronics, production of health-related materials, agriculture, etc. In this context, biodegradable nanocomposites offer new and exciting possibilities. This book deals with the development of functional polymer nanocomposites that can undergo biodegradation in different media, including biological systems, soils, landfills, etc. Original and review articles covering aspects of polymer science and technology, such as synthesis, processing, characterization, properties, and applications of functional biodegradable nanocomposites for different applications, are included in this book

Development of Metal Matrix Composites Using Microwave Sintering Technique

In this book chapter, aluminum (Al)-based metal matrix composites (AMMCs) with various reinforcing ceramic particles, such as SiC, Si3N4, and Al2O3, were produced by microwave sintering and subsequent hot extrusion processes. The role of various nano/micro-sized reinforcements in altering the structural, mechanical, and thermal properties of the microwave-extruded composites was systematically studied. The X-ray diffraction (XRD) patterns indicated that the main components were Al, SiC, Si3N4, and Al2O3 for the studied Al-SiC, Al-Si3N4, and Al-Al2O3 composites, respectively. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) elemental mapping confirm the homogeneous distribution of reinforcing particles in the Al matrix. Mechanistic studies revealed that the Al-Si3N4 metal matrix composite exhibited superior hardness, ultimate compression/tensile strength, and Young’s modulus, while having a lower coefficient of thermal expansion compared to other studied Al composites. Findings presented are expected to pave the way to design, develop, and synthesize other aluminum-based metal matrix composites for automotive and industrial applications

Preparation and characterization of polyethylene based nanocomposites for potential applications in packaging

The objective of my work was to develop HDPE clay nanocomposites for packaging with superior barrier (gas and water) properties by economical processing technique. This work also represents a comparative study of thermoplastic nanocomposites for packaging based on linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon12. In this study properties and processing of a series of linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon 12 nanocomposites based on Na-MMT clay and two different aspect ratio grades of kaolinite clay are discussed. [Continues.

Nanoparticle Dynamics in Polymer Melts

The effect of small amounts of nanoparticles on the melt-state linear viscoelastic behaviour is investigated for different polymer-nanoparticles model systems characterized by poor polymer-particles interactions and low particle contents.contents. The drastic increase of the rheological properties with respect to the matrices is related to the formation of a filler network above a critical particles volume fraction. Once formed, the filler network exhibits an elastic feature that mixes with the intrinsic viscoelastic response of the polymer matrix, resulting in a complex Φ- and ω-dependent viscoelastic response of the nanocomposite. However, we show that the contributions of filler network and suspending medium can be decoupled due to the weak polymer-particle interactions and the differences in temporal relaxation scales. The adopted approach is validated through the building of a master curve of the moduli, which reflects the scaling of the elasticity of composites along the viscosity of the suspending medium. The two-phase model well works irrespective of the structure of the filler network, making evident the strict interrelationships between the structure, both on nano- and micro-scale, and the melt- state behaviour of the studied PNCs