The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
The tensile properties and the fracture toughness, using the essential work of fracture method, of melt-compounded polymer nanocomposites (NCs) based on polypropylene with different organo-modified clays (montmorillonite) and maleic anhydride grafted PP coupling agents were studied. Improvements in tensile and fracture properties were observed, which were related to the level of dispersion of clay particles, both at the nano- and the micro-scale. Clay micro-particles acted as void nucleation sites within the PP matrix. The highest tensile properties and highest fracture toughness were obtained for the PP/clay compound showing high particle density with good particle-matrix adhesion, which led to intermediate void nucleation but extensive fibrillation.
The preparation of nanoclay-reinforced polyolefin nanocomposites by means of melt processing was investigated. Different formulations and processing conditions were used in order to optimize the chemical interaction between the polymer matrix and the clay so as to maximize the performance. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and differential thermal analysis (DTA) were used to study the chemical interactions between the polymer and the organo-nanoclay as well as the dispersion of the nanoclay. It was shown that the various parameters (chemistry and concentration of organo-intercalant, mixing conditions, and especially chemistry and concentration of coupling agent) all affect the ultimate performance and that the interactions between them must be taken into consideration in developing nanocomposite systems.
An alternative route to prepare polymer-clay nanocomposites using supercritical carbon dioxide (scCO2) is described. The presence of clay nanoparticles significantly influences the morphology, foaming process and crystallization of a polymer when processed in scCO2. Intercalated structures are successfully produced in the presence of scCO2 even when favorable interactions between the polymer and the clay are not present. The effect of scCO2 on the intercalation process is analyzed for a variety of polymer systems both with modified and unmodified clays. By controlling the hydrophilicity of the polymer and clay systems, specific understanding of the effect of scCO2 on the structure and morphology of the nanocomposites is obtained. Experimental results show significant increases in the clays d-spacings for scCO2-treated samples. This behavior is consistent regardless of the nature of the polymer, showing significant amounts of intercalation even in purely hydrophobic polymers.
Polypropylene based nanocomposites reinforced with up to 25 vol% exfoliated graphite nano-platelets were fabricated using extrusion and injection molding. The mechanical and electrical properties of the graphite nanocomposites were investigated and compared to the properties of polypropylene-based composites reinforced with other conductive materials, e.g., carbon black and carbon fibers. It was found that the graphite nano-platelets were the most effective at increasing the modulus of the polypropylene and comparable to the other materials in terms of percolation threshold.
Recently we have invented a novel method for fabricating polypropylene (PP)/clay nanocomposites by applying the electric field. Electric field was found to facilitate destruction of the layer-stacking and separation of the silicate layers by the penetration of polymer chains into silicate galleries. This was evidenced by rheological measurements, X-ray diffraction and Transmission electron microscopy. From this observation, we could find that the microstructural change of PP/Clay nano-composites induced by the electric field is a very important factor to control the performance and morphology of the material. In this study, real-time evolution of PP/clay nanocomposites under electric field using in situ wide-angle X-ray scattering (WAXS) analysis will be presented. We designed a heating block equipped with electric circuits to apply electric field on the molten state of PP/clay composites. The real-time microstructural changes of PP/clay nanocomposites under AC electric field of 1kV/mm and 60 Hz were analyzed by the result of 2D WAXS data. This will be compared with that under DC electric field. We will present the kinetics of melt intercalation process under electric field.
By oscillating the injected resin stream in liquid composite molding, the mold filling time can be significantly reduced. Flow enhancement is achieved because of the shear-thinning characteristics of typical polymer resins, as the effective shear rate of the resin is increased by oscillation of the resin within the fiber preform and the viscosity of the resin is correspondingly reduced. An experimental apparatus has been developed which consists of one-dimensional flow within a fiber preform and a vibrating piston which forces the inlet resin stream to oscillate. Experiments have been conducted using a polyacrylamide/water solution to simulate the polymer resin, and effects of oscillation amplitude, frequency and fiber volume fraction have been investigated. A simple analytical model has also been developed, and experimental results confirm the predicted trends in the amplitude, frequency and volume fraction effects on flow enhancement.
A fast, inexpensive and environmentally benign process requiring only UV light and air for the surface treatment (oxidation) of reinforcing fibers has been developed that represents a substantial improvement over existing methods. In this new method, fibers are subjected to short wavelength ultraviolet (UV) light producing ozone from atmospheric oxygen. UV photons can also react with ozone to create monatomic oxygen, a highly reactive chemical species which is available to oxidize the fibers. Additionally, the UV photons can break chemical bonds on the fiber surface creating favorable conditions for reaction with ozone and monatomic oxygen. The result of this two-fold process is the rapid oxidation of the fiber surface that is essential to promote favorable interactions with the matrix in polymer composites. The effect of UVO treatment on the surface chemistry, tensile strength, and interfacial adhesion of a PAN based carbon fiber and an aramid fiber is reported.
Due to the geometric complexity of woven fabric composite materials, conventional Non-Destructive Evaluation (NDE) methods such as x-radiography and acoustic emission (AE) do not show microcracks well inside the materials. In this study, a simple and cost effective water uptake test as a NDE methodology for PMR-II-50/M60J (polyimide/carbon fiber) 4HS weave fabric composites is suggested. The short term water uptake test for 24 hours at 80°C has been performed before and after stress-thermal cycling experiments with the TAMU developed conduction heated stress-thermal cycling apparatus. The woven composite materials’ non-Fickian model during short term water uptake, that is, the rate of uptake initially increases rapidly followed by quick slow down associated with diffusion in cure-induced voids and cracks was modified by the effective diffusivity depending on crack densities. The suggested crack densities dependent diffusion model was compared with the experimental data. The application of the water absorption induced NDE was also re-evaluated by comparing to the results of the literatures in terms of crack closure by swelling and unloading of the existing load and matrix dissolution by hot water.
Selected fillers were incorporated to prepare polyetherimide composite. The influence of fillers on the thermo-oxidative stability of the composite was studied by thermogravimetric analysis. The results showed that at optical filler loading and characteristics, the polymer composite became superior in its thermo-oxidative stability that is very promising in widening the window of service temperature of polyimides for extremely high temperature conditions where most polymeric composites fail. The findings should prove useful in developing high-temperature polymer composites for aerospace and electronics applications.
This manuscript describes the processing techniques and processing windows used to produce carbon fiber reinforced nylon matrix composite panels. Preliminary mechanical property measurements were also made. Anionic polyamide 6 resin (casting grade) was polymerized in situ after infusion. Careful time and temperature control were necessary to obtain total fiber impregnation with subsequent complete polymerization. These advances will permit the use of affordable thermoset manufacturing processes such as Vacuum Assisted Resin Transfer molding (VARTM) or Resin Transfer Molding (RTM) to produce thermoplastic-matrix composite structures.
In this study, multi-axial warp knitted thermoplastic composites were fabricated by our-developed Micro-braiding technique. Cross-sectional observation, tensile test and 3 point bending test were performed. The composite with good impregnation state was obtained under appropriate molding conditions, consequently high mechanical properties were achieved. The multi-axial warp knitted fabric composite without unimpregnated region had the equivalent mechanical properties with unidirectional composite laminates. Moreover, new concept of continuative fabrication method was proposed.
A comprehensive measurement system analysis (MSA) on measurement of apparent viscosity using the slit die method was conducted. Nine materials and three operators with three repeats were used. P/T (precision to tolerance) and P/P (precision to process) ratios were estimated from gage R&R analysis. Repeatability was found to be greater than reproducibility. Slip analysis on the wood fiber composites indicated that these composites essentially flow by slip mechanism. Six Sigma methodologies with rigorous method development resulted in establishing control materials and implementing SPC in a manufacturing plant.
This paper focuses on the development of a new technology and process in order to manufacture natural fiber reinforced engineering thermoplastics like nylon 6. Natural fibers are not suitable reinforcements when high temperature melting (above 200°C) engineering thermoplastics is used as matrix materials because natural fibers start to degrade thermally at above 200°C. Small quantities of inorganic salts like lithium chloride were added to the nylon 6 during melt extrusion processing to depress its melting temperature. The final composites are injection molded into test specimen at the reduced processing temperatures of nylon 6. The molded plastics and composites are tested for mechanical and thermal properties. Natural fiber reinforced nylon 6 composites show improved tensile and flexural properties. The morphology of the fracture surfaces is observed using Environmental Scanning Electron Microscopy.
This paper presents the processing/structure/property relationships for artificial wood made from stretched PP/wood-fiber (WF) composites that have required strength and density. The die drawing of PP/WF composites causes a unidirectional orientation of the polymer molecules and enhances the mechanical properties significantly along the stretched direction. The drawing of the composites also lowers the density of artificial wood by generating voids at the WF and polymer matrix interface. The critical processing and materials parameters are identified. The effects of these parameters on the structure and the properties are also investigated.
Green composites were made from poly (lactic acid) (PLA) and cellulose fibers by extrusion followed by injection molding processing and their physico-mechanical properties were evaluated. The properties of PLA reinforced with varying amounts of wood pulp-based cellulose materials were studied. These composites possess superior thermal and mechanical properties based on the strong interaction between the PLA matrix and the cellulose fibers. It was found that the wood pulp-based cellulose fiber could be a good reinforcement candidate for the high performance biodegradable polymer composites.
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 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.
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.
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.
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.
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