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Biobased Composites Manufactured through a Reactive Extrusion of Maleated Wood Particles
Biocomposites such as particleboard and medium density fiberboard are currently made with formaldehyde-containing adhesives. Since the government is continuously developing and implementing very stringent regulations to eliminate formaldehyde emissions into the environment, alternative approaches must be developed to replace these adhesives. This study examined the concept of using a reactive extrusion process as a means of developing a new, formaldehyde-free binding system for wood composite products. The surfaces of wood particles were modified by grafting maleated polyethylene through a continuous reactive extrusion process. Chemical changes resulting from this treatment were followed by studying the FTIR and XPS spectra. The modified wood particles were compression-molded into panels, which were tested for bending properties. Both FTIR and XPS data revealed that the chemical reactions have taken place between the hydroxyl groups of wood particles and maleated polyethylene. The modulus of rupture (MOR) results showed that the composite panels compared favorably with current standard requirements for particleboard.
Coupling Efficiency of Maleated Polyethylene Copolymers in Wood Fiber-High Density Polyethylene Composites
Coupling efficiency of several maleated polyethylene (MAPE) copolymers was investigated in this study. Interfacial bonding strength, flexural modulus, and other mechanical properties of wood fiber-high density polyethylene (HDPE) composites were related to coupling agent type, molecular weight, acid number, and concentration. Acid number and molecular weight were two important indexes for interfacial adhesion. Acid number had negative influence on interfacial bonding strength at high concentration, whereas molecular weight had positive effects. Backbone structure of coupling agents also affected interfacial bonding strength. MAPEs with linear low-density polyethylene (LLDPE) backbone were better than those with HDPE and low-density polyethylene (LDPE) structure. Compared with untreated composites, modified composites with 50% of wood fiber were improved in interfacial bonding strength by 140% on maximum and flexural modulus by 29%. According to experimental results, coupling agent 100D, 226 D, and C16 were the best coupling agents. Therefore, coupling agents with larger molecular weight, moderate acid number, and low concentration were preferred to improve the interfacial bonding of the resultant composites.
Mechanical Properties of Carbonized Bamboo Fiber Reinforced Biodegradable Polymer Composite
The mechanical properties of biodegradable polymer composite with carbonized bamboo fibers were evaluated. Poly (butylene succinate) (PBS) was used as the biodegradable plastic matrix while the condition of carbonization was varied. By increasing fiber content, tensile modulus was confirmed to increase. In particular, the tensile modulus of composite filled with semi-carbonized bamboo displayed higher values than the uncarbonized bamboo fibers composite. The values of tensile strength decreased according to the increase of fiber content; however, the carbonized bamboo fiber composites experienced less decrease than the uncarbonized ones. The surface resistivity of carbonized bamboo fiber composites was lower than that of bamboo fibers and also decreased with the increase in fiber content in each case.
Development of Thermoplastic Electrolytes and their Ionic Conductivity
The ionic conductivity of polyethylene oxide film complexed with copper acrylic acid salt (PEO-Cu(AA)2) as well as copper and copper chloride were studied. The effects of the interaction between PEO and salts on their conductivities are discussed with the help of thermal analysis and vibration spectroscopy. Bulk conductivity values were evaluated from the alternating current measurement by constructing impedance plots. PEO-Cu and PEO-Cu(AA)2 complexes exhibited the typical ionic conductive behavior of polymer electrolytes. The ionic conductivity of PEO-Cu(AA)2 complex at room temperature yielded the magnitude of conductivity at 10-6 Seimen/cm.
Electrical Properties of Carbon Nanofiber-Modified Thermotropic Liquid Crystalline Polymers
Vapor-grown carbon nanofibers (CNFs) were incorporated into a thermotropic liquid crystalline polymer (TLCP, Vectran V400P) to investigate the electrical and mechanical properties of the composite. The percolation threshold was observed in composite films at 5 wt% CNF. With increasing CNF content (up to 5 wt%), the longitudinal tensile strength decreased, whereas the transverse strength increased. Thus, with increasing CNFs, the composite films became not only more electrically conducting but also displayed more balanced longitudibal/transverse properties. The morphological features of CNF-modified TLCP were analyzed by X-ray diffraction. Results suggest that the CNFs lead to the disruption of the TLCP orientation, and may help produce TLCP-based films that have balanced in-plane properties.
Application of Radiation Cross-Linking for the Improvement of the Short-Time Thermo-Mechanical Properties of 3D-MID's
Materials with compounded cross-linking additives, e.g. PA6, PA66 and PBT, were developed to improve the heat resistance of engineering thermoplastics during high short-time temperature-loads. Cross-linking of plastics is a process, with which the individual plastic molecules are chemically bonded together. This process is released through, e.g. electron beam irradiation. The temperature-dependent irreversible mobility of the molecules decreases through cross-linking. Therefore, the softening range is shifted to higher temperatures depending on the degree of cross-linking. This behaviour is considerably interesting for the development of MID-assembles, which will be processed in continuative processes of the electronic production, e.g. soldering. The following paper offers an overview of the potentials of iradiation cross-linked PA for MID-applications.
A Novel CNTs/Polymer/PE Composite with High Electromagnetic Shielding
A sandwich structure composite employing polyethylene and multi-walled carbon nanotubes/polymer, which is synthesized by in-situ polymerization on well aligned carbon nanotubes, is demonstrated with high electromagnetic shielding effectness. The shielding effectness of composites related with the orientation of carbon nanotubes embedded in the polyethylene was studied systematically. The shielding effectness of composites with parallel with the normal of polyethylene matrix were measured to be higher than those with carbon nanotubes perpendicularly to the composite surface or randomly oriented with frequency ranging from 0.3 GHz to 3.0 GHz.
Distribution of a Minor Solid Constituent in a Transfer Molded Leadframe Microcircuit Package
This study investigates the spatial distribution of a minor particulate constituent in a transfer molded leadframe microcircuit package. The package has been polished at three levels parallel to its top surface. Levels 1 and 2 are above the die and leadframe while level 3 is just below the top surface of the die and leadframe. The distributions of area fraction and size of the particulate were analyzed for each level using micro-photography. Comparisons were made at different levels as well as different positions within each level. Both size and spatial distributions of the particulate material are evidently non-uniform, and its relations with gate, die and leadframe are interpreted. ANOVA tests were conducted to assess the statistical significance of the variations.
Three-Dimensional CAE of Wire-Sweep in Microchip Encapsulation
Wire Sweep is a common molding problem encountered in microchip encapsulation. The resin melt flow will exert drag force on wires and hence causes deformation of wires. In this paper, an integrated CAE of wire sweep is proposed to help engineer to evaluate and optimize the encapsulation process. The resin flow is calculated by a true 3D thermal flow solver based on a highly flexible prismatic element generation technique. Thanks to the efficiency of the proposed methodology in terms of CPU time and memory requirement, the industrial packages with complex geometry and high pin count can be analyzed with minimum model simplification. Furthermore, a user-friendly integrated environment is also developed to link the flow analysis with structure analysis to provide the total solution for wire sweep assessment. The developed approach proved from numerical experiments to be a cost-effective method for true 3D simulation of wire sweep in microchip encapsulation
Three-Dimensional Dynamic Simulation of Paddle Shift during Semiconductor-Chip Encapsulation
In this paper, the movement of the paddle during the semiconductor-chip encapsulation process is simulated dynamically. The non-uniform pressure distribution across the paddle will cause the paddle to shift during filling. The movement of the paddle will in turn cause a change in cavity thickness, and thus will affect the flow. This interaction between paddle shift and flow has been simulated. A three-dimensional finite-element method is used for the flow analysis. The simulation results are evaluated using an example case. The effects of mold temperature and filling time have also been examined.
Molding Analysis for Underfill of Flip-Chip Packages
Nowadays, underfill of flip chip is often driven by capillary force to dispense the space between chip and substrate. The flow is very slow and could result in incomplete dispensing or voids. Therefore, as the chip size increases, the dispensing problems become more serious. For this reason, it is critical for flip-chip technology to speed up the encapsulation process and avoid possible defects.This paper setup an experiment to study the influences of bump design, such as gap height, bump pitch and bumped patterns, on the underfill of flip-chip package. These studies could be used to build up the knowledge of underfill process.
The Analysis on the Fatigue Life of Flip Chip Package under Cyclic Thermo-Mechanical Loading
This study focuses on the reliability of flip chip package under the loading of cyclic temperature. This study shows thorough modeling and analysis of using ANSYS to simulate the thermal conduction and the mechanical behavior of flip chip package. The results reveal that the deflection is caused by the difference of material properties of the components, as such, the maximum equivalent plastic strain of solder bumps always happens at the farthest place from the symmetrical surface of models where the fatigue destruction occurs most easily. Further, temperature cycle test (TCT) was employed to study issues of reliability. The fatigue life was calculated by fatigue-stress and fatigue-strain method respectively in different cycles, material properties, and processes.
Structural Analysis of DC-DC Converters
The compact DC-DC converts consist of one aluminum substrate and two FR-4 substrates which hold electronic components, and molding epoxy. Due to its structural complexity, the device could be easily failed during the thermal cyclic test.This paper presents the complete CAE modeling and integrated analysis of DC-DC converters which can be used to design a better product. A detail 3D model of converters is constructed to understand the behavior of all important components under the thermal cyclic test. The results show the weakest solder-joint spot which can be verified with experimental failure. Some geometrical parameters are also studied to show their importance.
Synthesis and Properties of Polymer Blend Nanocomposites. Part II. Thermoplastic Olefin (TPO)
Nanocomposites with organically treated montmorillonite derived from layered silicates in various PP/EPDM blends were prepared by direct melt intercalation in an internal mixer. In these nanocomposites, the nanoclay reinforcement is constrained to lie selectively either in the continuous matrix or in the dispersed phase or both phases of a thermoplastic olefin. The morphology as well as mechanical properties of the nanocomposite blends are strongly affected by the selective reinforcement of each phase. Morphology characterization by x-ray diffraction (XRD) and transmission electron microscopy (TEM) provide the basis for understanding the observed structure-property relationships in this class of materials.
Rheological Characterization of Polystyrene-Clay Nanocomposites as they Relate to the Degree of Dispersion
Polymer nanocomposites with as little as 2-vol. percent of layered silicate can dramatically improve tensile modulus, strength, and heat distortion temperature without significant loss of impact strength. Such improvements will have major impact in the material industry and technology. Because viscoelastic measurements are highly sensitive to the nanoscale and mesoscale structure of polymeric materials, when combined with X-ray Scattering, electron microscopy, thermal analysis, and mechanical property measurements, they will provide fundamental understanding of the state and mechanism of exfoliation of layered silicate in polymer matrix. In addition, understanding rheological properties of polymer nanocomposites is crucial for application development and understanding polymer processability.The degree of intercalation, exfoliation, and dispersion has been traditionally characterized by XRD and TEM. While both of them are very effective tools, both are limited by only probing a small volume of the sample and are too costly for routine characterization of nanocomposites. Melt rheology can quantify via a global average on the degree of intercalation/exfoliation/dispersion across whole nanocomposite test specimens usually around 2 grams of samples. It will be less ambiguous than other techniques (e.g. TEM) in quantifying exfoliation/dispersion. In addition, it will be easier to perform than TEM and XRD thereby opening up the possibilities of performing routine studies to better understand the influence of material options and processing conditions for improving nanocomposite exfoliation/dispersion. In this report, the effects of clay dispersion/exfoliation on the viscoelastic properties of polymer/clay nanocomposites are investigated using dynamic mechanical measurements, dynamic shear measurements, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Polystyrene/clay hybrid materials with different degree of dispersion/exfoliation were prepared by solve
Effect of Clay Surface Modification on the Polymer Nanocomposite Foam Structure
Nanoclay can work as a nucleation agent to control foam cell structure and reinforcement to enhance foam properties. In this paper, the clay surface is modified by a reactive quaternary ammonium surfactants and grafted with either poly(methyl methacrylate) (PMMA) or polystyrene (PS). The polystyrene and the polymer modified clay nanocomposites are synthesized by in-situ polymerization and extrusion compounding. By using CO2 as the foaming agent, the nanocomposite foams are prepared in a single screw extruder. It is found that the surface modification has a great influence on the foam morphology. The presence of more CO2-philic PMMA on the clay surface leads to a lower melt viscosity.
Graphene Nanoplatelet Reinforced Polymer Coatings
Fabrication of carbon nanotubes is expensive, particularly for the purifying process required to make useful nanotube polymer composites. Instead of trying to discover lower cost processes for nanotubes, we seek to develop an alternative nanoscale carbon material with comparable properties that can be produced cost-effectively and in larger quantities for composites applications. This new class of nano material is herein referred to as nanoscale graphene plate (NGP). This paper introduces the novel processing ideas for NGP and some mechanical and electrical properties of the NGP reinforced polymers.
Melt Rheology of Polylactides
Polylactides (PLAs) have been known for several decades and have recently gained considerable commercial significance. This development makes it urgently desirable to have the rheological properties of these materials well-characterized. In this study, rheological and thermal measurements were made on a comprehensive and well-characterized set of homopolymers and copolymers spanning wide ranges of molecular mass and stereoisomer proportions. Temperature dependencies of the time-temperature superposition curves were obtained. Data were correlated utilizing a viscoelastic model enabling the development of a simple Excel spreadsheet for predicting linear viscoelastic properties as a function of molecular weight and temperature.
Novel Controlled Drug Release Biodegradable Polymers Systems
Biodegradable polymers, in particular polylactide and polyglycolide systems, having started out predominantly in the degradable sutures market, are now finding increasing use for controlled drug delivery and tissue engineering, where their use as temporary substrates or devices provides significant therapeutic advantages. The idea of using them as micro particles to prolong delivery of drugs have already been commercialized. This paper describes some work focusing on using these polymers as novel structures for localized and multiple drug delivery. The development of a dual drug eluting stent will be described to treat stenosis of coronary blood vessels, pulmonary airways or urological passages. The stents are inserted non invasively into and anchored to be resident in the body for a prescribed period to release drugs according to a prescribed profile and bio-erosion rate, hence eliminating the need for a second surgical procedure. Another application presented is the development of novel copolymers of PLA particles with stealth ability to evade the immune system and hence achieve protracted blood lifetimes, allowing efficacious therapy in especially cancer treatment. With suitable modifications, such nanoparticles may also be made to act as non-viral gene vectors to be used in delivering gene payloads to the nucleus.
Mechanical Responses in Biomimetic Polymer Hydroxyapatite Nanocomposites
In situ composites of hydroxyapatite (HAP-the mineral component of natural bone) were synthesized in our previous work. The in situ composites exhibit improved recovery and smaller plastic strains than the ex situ composite systems. The role of synthetic macromolecules in controlling the mineralization of HAP is shown to be the primary reason for the improved mechanical responses in these material systems. The control of macromolecules on mineralization of HAP and resulting bulk properties of the composite are similar to that of collagen in natural bone. This process thus represents a biomimetic method for control of mechanical responses in polymer-HAP composites. Mechanical responses of the composite after soaking in a simulated body fluid (SBF) are investigated using X-ray diffraction, scanning electron microscopy and infrared spectroscopy. Superior response of the composites (higher modulus and strength) is observed under SBF as compared to soaking in water. Response of these composites under strain rates typical for human bones is also investigated
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