David A. Schiraldi

Fibers from polypropylene/nano carbon fiber composites

Fibers from polypropylene and polypropylene/vapor grown nano carbon fiber composite have been spun using conventional melt spinning equipment. At 5 wt% nano carbon fiber loading, modulus and compressive strength of polypropylene increased by 50 and 100%, respectively, and the nano carbon fibers exhibited good dispersion in the polypropylene matrix as observed by scanning electron microscopy.

Processing, structure, and properties of fibers from polyester/carbon nanofiber composites

Poly(ethylene terephthalate) (PET) resin has been compounded with carbon nanofibers. The amount of carbon nanofibers utilized in each case was 5 wt.%. Compounding methods included ball-milling, high shear mixing in the melt, as well as extrusion using a twin-screw extruder. PET/CNF composite resins were melt-spun into fibers using the conventional PET fiber spinning conditions. Morphology and mechanical properties of these composite fibers have been studied. The results show that CNFs can be incorporated into PET matrix with good dispersion. Compressive strength and torsional moduli of PET/CNF composite fibers were considerably higher than that for the control PET fiber.

Processing and properties of poly(methyl methacrylate)/carbon nano fiber composites

Single wall carbon nanotubes, multi-wall carbon nanotubes, as well as carbon nano fibers (CNF) are being used for reinforcing polymer matrices. In this study, poly(methyl methacrylate) (PMMA) nanocomposites have been processed by melt blending, containing two different grades (PR-21-PS and PR-24-PS) of CNF manufactured by Applied Sciences Inc. The amount of nano fibers used was 5 and 10 wt%, respectively. The PMMA/CNF composites were processed into 4 mm diameter rods and 60 μm diameter fibers using small-scale melt spinning equipment. At 5 wt% CNF, composite rods as well as fibers show over 50% improvement in axial tensile modulus as compared to the control PMMA rod and fibers, respectively. The reinforcement efficiency decreased at 10 wt% CNF. The PMMA/CNF nanocomposite fibers also show enhanced thermal stability, significantly reduced shrinkage and enhanced modulus retention with temperature, as well as improved compressive strength. The CNF reinforcement efficiency has been analyzed using the modified Cox model.

Oxygen barrier properties of crystallized and talc-filled poly(ethylene terephthalate)

The improvement in oxygen barrier properties of poly(ethylene terephthalate) (PET) by incorporation of an impermeable phase such as crystallinity or talc platelets was examined. Crystallinity was induced by crystallization from the glassy state (cold crystallization). Microlayering was used to create talc-filled structures with controlled layer architecture. The reduction of permeability in crystallized and talc-filled PET was well described by Nielsens model. Changes in permeability of crystalline PET could not be ascribed to the filler effect of crystallites only. Our data on solubility, obtained on the basis of measurements of the oxygen transport coefficients, confirmed a previous finding that the amorphous phase density of PET decreases upon crystallization. The data were amenable to interpretation by free volume theory. Talc-filled materials processed by different methods showed the same permeability; however, much better mechanical properties were achieved by microlayering.

Clay aerogel/cellulose whisker nanocomposites: a nanoscale wattle and daub

Aerogels based on either clay or cellulose nanofibers are representatives of an emerging class of structural materials with ultra-low density. Both types of aerogels are made from abundant raw materials and are formed through environmentally friendly freeze-drying processes. Due to the ultra-low-density layered superstructure that results from templating by the ice crystal morphology, the neat aerogels are unfortunately often rather fragile. The present study explores inorganic/organic hybrid aerogels that comprise montmorillonite and cellulose nanofibers isolated from tunicates. Dynamic mechanical testing revealed that, especially at low densities, these materials exhibit compressive strengths that are significantly higher than predicted by simple additive behavior of the properties of the individual components. At first glance, the data seem to suggest the formation of a nanoscale “wattle-and-daub”, in which the two components (mud-like clay and straw-like cellulose whiskers) complement each other. It appears that the main cause for this synergy is the enhanced formation of three dimensional network structures during the freeze-drying process.

Reinforcement of Poly(ethylene terephthalate) Fibers with Polyhedral Oligomeric Silsesquioxanes (POSS)

Poly(ethylene terephthalate) (PET)-based composite fibers were prepared by melt spinning three types of PET/polyhedral oligomeric silsesquioxane (POSS) composites. These composites were made by either melt blending POSS with PET at 5 wt% loading level (non-reactive POSS and silanol POSS) or by in-situ polymerization with 2.5 wt% reactive POSS. Significant increases in tensile modulus and tensile strengths were achieved in PET fibers with non-reactive POSS at room temperature. The hightemperature modulus retention was found to be much better for PET/silanol POSS fiber when compared to that of control PET. Although other PET/POSS nancomposite fibers tested did not show this high retention of modulus at elevated temperatures, PET/isooctylPOSS nanocomposite fibers did show increased modulus at elevated temperature compared to that of PET. Higher compressive strengths, compared to PET fibers, were observed for all three nanocomposite fibers. Gel permeation chromatography measurement suggested that there is no significant change in molecular weight during preparation of PET/POSS nanocomposites. SEM observations suggest that there is no obvious phase separation in any of the three PET/POSS systems. Crystallization behavior and thermal stability of the composite were also studied. The fiber spinning and mechanical performance with 10 and 20 wt% of trisilanolisooctyl POSS2 were also investigated1 the composites with higher concentrations of this nanofiller can be spun without any difficulty. At room temperature, the fiber tensile modulus increased steadily with the POSS concentration while fiber tensile strength showed no significant change. The elongation at break decreased significantly with increasing of POSS concentration. The high-temperature moduli of PET/POSS nanocomposite fibers were found to be rather variable, likely due to the modest compatibility between filler and polymers, which can lead to structural anisotropy within the composite.

Biodegradable Pectin/Clay Aerogels

Biodegradable, foamlike materials based on renewable pectin and sodium montmorillonite clay were fabricated through a simple, environmentally friendly freeze-drying process. The addition of multivalent cations (Ca(2+) and Al(3+)) resulted in apparent cross-linking of the polymer and enhancement of aerogel properties. The compressive properties increased as the solid contents (both pectin and clay) increased; moduli in the range of 0.04-114 MPa were obtained for materials with bulk densities ranging from 0.03 g/cm(3) to 0.19 g/cm(3), accompanied by microstructural changes from a lamellar structure to a cellular structure. Biodegradability of the aerogels was investigated by detecting CO2 release for 4 weeks in compost media. The results revealed that pectin aerogels possess higher biodegradation rates than wheat starch, which is often used as a standard for effective biodegradation. The addition of clay and multivalent cations surprisingly increased the biodegradation rates.

Development of Biodegradable Foamlike Materials Based on Casein and Sodium Montmorillonite Clay

Biodegradable foamlike materials based on a naturally occurring polymer (casein protein) and sodium montmorillonite clay (Na+ -MMT) were produced through a simple freeze-drying process. By utilizing DL-glyceraldehyde (GC) as a chemical cross-linking agent, the structural integrity of these new aerogels were remarkably improved when compared to those of the control system (without GC), with a minimal increase in the density from 0.11 to 0.12 g cm⁻³. The degree of perfection of the foamlike structures was another parameter that had a significant influence on the physical and thermal performances of the low density composites. The biodegradability of the aerogels was investigated in terms of the carbon dioxide (CO₂) evolution for up to 8 weeks in compost media under controlled conditions.

Elastic, low density epoxy/clay aerogel composites

Clay aerogels are ultra-low density materials formed by the freeze-drying of aqueous clay gels. While unmodified clay aerogels exhibit generally poor mechanical properties, incorporation of polymers into these structures can greatly increase their strengths and moduli; such polymer/clay aerogel composites have potential for use in a range of structural and insulation applications. Polymer/clay aerogel composites were formed by a new process in which water-soluble thermoset epoxy precursors are reacted within a clay hydrogel, which is then freeze-dried to produce the polymer/clay aerogel composites. The compressive properties of these polymer/clay aerogel composites greatly exceed those of plain clay aerogels; moreover, some of these composites exhibit novel elastomeric behavior, withstanding and recovering large amounts of compressive strain without failure or significant permanent deformation.

Two-photon 3D optical data storage via aggregate switching of excimer-forming dyes.

N S Current optical data storage (ODS) technologies use onephoton-absorption processes to write data by locally changing the optical properties of the medium. [ 1 , 2 ] Since the lateral dimensions of spots that can be written are near the diffraction limit, signifi cant capacity increases require new approaches such as storage in three dimensions. DVDs, which comprise up to four individually addressable storage layers, exemplify the potential of this concept, but the complexity of producing and using multilayer systems increases with the number of layers. In bulk materials, changes can be confi ned in the third dimension via nonlinear optical processes, such as two-photon absorption (TPA). [ 3– 6 ] We have developed a novel ODS system that relies on the optically-induced switching of the aggregation state and fl uorescence of a TPA dye in a polymer matrix. Welldefi ned, ∼ 3 × 3 × 6 μ m-large voxels were written with single focused laser pulses and read by confocal laser scanning microscopy. Such ODS systems are easily produced and promise a storage capacity of up to several Tbytes on a DVD-size disk, which is ∼ 100× higher than that of current commercial ODS technologies. [ 6 , 7 ]