Lawrence Drzal - Academia.edu (original) (raw)

Papers by Lawrence Drzal

This research investigates the interactions between exfoliated graphite nanoplatelets (graphene s... more This research investigates the interactions between exfoliated graphite nanoplatelets (graphene sheets ~10nm thickness, ~1um diameter), a new nano-material developed by Drzal’s group, with polyolefin based thermoplastics. It provides an understanding about how the processing method/conditions used affect the properties of xGnP/PP nanocomposites i.e., mechanical, thermal, barrier properties; electrical conductivity and percolation threshold and therefore can lead to materials with desired properties. A significant development is a new compounding method, which is more effective than the solution method widely used, in terms of lowering the percolation threshold of thermoplastic nanocomposites, and maintaining the platelet morphology of xGnP. The feasibility of using xGnP-PP nanocomposites was investigated by evaluating the properties of this system and comparing the xGnP-PP with composites made with commercial available reinforcements.

Carbon fibers require surface treatment to establish suitable adhesion to polymeric matrices. In ... more Carbon fibers require surface treatment to establish suitable adhesion to polymeric matrices. In general these surface treatments are classified in three categories: anodic oxidation, a wet process where solution concentration and amperage must be maintained; exposure to ozone gas at elevated temperature; and treatment in caustic solutions such as nitric acid. Surface treatments produce improved composite properties through a two part mechanism. First, a weak, defect-laden outer layer is removed from the carbon fiber surface, resulting in a stronger surface to sustain shear loading. The second contribution of surface treatments is the deposition of chemical functionalities, most notably oxygen containing moieties, which improve wetting and bonding between the fiber and matrix [1].

Since the late 1990’s, research has been underway in our group at Michigan State University to in... more Since the late 1990’s, research has been underway in our group at Michigan State University to investigate the fabrication of new nano-size carbon material, exfoliate graphite nanoplatelets [xGnP]. The xGnP is fabricated from natural graphite and can be used as a nanoreinforcement for polymers as an alternative to expensive carbon-based nanomaterials. The thickness of the xGnP became around 5-10nm. The diameter can be controlled from sub-micron level to few hundred um, indication the aspect ratio can be controlled. The surface area of the material reached more than 100m/g. Since graphite is the stiffest material found in nature (Young’s Modulus = 1060 MPa), having a modulus several times that of clay, accompanied with excellent strength, electrical and thermal conductivity, the xGnP should have similar properties to carbon-based nanomaterials, including carbon nanotubes, nanofibers, and fullerenes, yet the estimated cost is fur less than these materials. The cost of the graphite nan...

Many research efforts have been focusing on exfoliated clay systems, the same nanoreinforcement c... more Many research efforts have been focusing on exfoliated clay systems, the same nanoreinforcement concept can be applied to another layered material, graphite. The key to utilizing graphite as a platelet nanoreinforcement is in the ability to exfoliate this material. If the appropriate surface treatment can be found for graphite, its exfoliation and dispersion in a polymer matrix will result in a composite with not only excellent mechanical properties but electrical properties as well, opening up many new structural applications as well as nonstructural ones where electromagnetic shielding and high thermal conductivity are required. In this research, a special thermal treatment was applied to the graphite flakes to produce exfoliated graphite reinforcements. Intercalated natural crystalline graphite compounds [GICs] were formed followed by exfoliation and milling to produce sub-micron graphite flakes. SEM and TEM images showed that the average size of graphite became 0.86 um with a th...

The objective of this research is to develop a fundamental understanding of adhesion of aramid fi... more The objective of this research is to develop a fundamental understanding of adhesion of aramid fibers to an epoxy matrix. In general, aramid fibers are para phenylene terephthalamide, rod-like polymers having a high degree of orientation and high crystallinity. Although these para type aramid fibers have high strength and high modulus, their surface is relatively inert. For composite applications it is necessary to improve the adhesion between fibers and matrices to improve the composite properties. For aramid fibers in tire rubber applications, an epoxy containing coating is placed on the aramid fiber bundle and given a high temperature treatment prior to incorporation into tire rubber. Investigation of this high temperature treatment has led to the conclusion that a minimum temperature of 240C produces a significant number of chemical bonds between the matrix epoxy groups and the amide groups on the aramid fiber surface which produces a substantial increase in fibermatrix adhesion...

Free radical cured thermosetting vinyl ester resins have superior toughness and chemical resistan... more Free radical cured thermosetting vinyl ester resins have superior toughness and chemical resistance in comparison to unsaturated polyester. The use of vinyl ester composites reinforced with carbon fibers requires an improvement in the fiber-matrix adhesion levels. Previous data has shown that the application of a lightly cross-linked aminecured epoxy sizing to the carbon fiber surface creates a beneficial interphase between the carbon fiber and vinyl ester resin matrix resulting in a substantial increase in fiber-matrix adhesion and the sizing has a optimum thickness . However, the exact mechanism by which this coating improved adhesion is not known. Vinyl ester resin can undergo as much as 10% volume shrinkage with cure while typical epoxy systems undergo only 3-4% shrinkage during cure . The cure volume shrinkage could have induced significant stresses in the fiber/matrix interphase. This could be the one of the most important factors that lowers the adhesion between carbon fiber ...

Since the late 1990’s, research has been underway in our group at Michigan State University to in... more Since the late 1990’s, research has been underway in our group at Michigan State University to investigate the fabrication of new nano-size carbon material, exfoliated graphite nanoplatelets [xGnP]. The xGnP is fabricated from natural graphite and can be used as nanoreinforcements for polymers as an alternative to expensive carbon-based nanomaterials. Extenisve work in our lab has produced a xGnP around 5-10 nm with a surface area larger than 100 m 2 /g. The diameter (and hence the aspect ratio) can be controlled from sub-micron level to few hundred micrometers. Since graphite is the stiffest material found in nature (Young’s Modulus = 1060 MPa), having a modulus several times that of clay, accompanied with excellent strength, electrical and thermal conductivity, the xGnP should have similar properties to carbon-based nanomaterials, including carbon nanotubes, nanofibers, and fullerenes, yet the estimated cost is far less than these materials. The cost of the graphite nanoplatelets ...

Fibers

Compatible interlayers must be coated on reinforcing fibers to ensure effective stress transfer f... more Compatible interlayers must be coated on reinforcing fibers to ensure effective stress transfer from the polymer matrix to the fiber in high-performance polymer composites. The mechanical properties of the interlayer, and its interfacial adhesion on both interfaces with the fiber and polymer matrix are among the key parameters that control the performance of polymer composite through the interphase region. Plasma-synthesized interlayers, in the form of variable materials from polymer-like to glass-like films with a Young’s modulus of 10–52 GPa, were deposited on unsized glass fibers used as reinforcements in glass fiber/polyester composites. Modulus Mapping (dynamic nanoindentation testing) was successfully used to examine the mechanical properties across the interphase region on cross-sections of the model composite in order to distinguish the fiber, the interlayer, and the modified and bulk polymer matrix. The interfacial shear strength for plasma-coated fibers in glass fiber/poly...

Contemporary vehicles utilize a mix of materials in their construction consisting of metals, plas... more Contemporary vehicles utilize a mix of materials in their construction consisting of metals, plastics, and composites. These materials must possess suitable surface properties to achieve desired performance when these parts are adhesively bonding or painted for field service. Surface preparation methods now in place oftentimes use solvents or caustics, an increasingly unacceptable approach in an era of mounting environmental regulations. New methods of surface preparation are called for that are environmentally benign and economically feasible while meeting the stringent quality standards of the automotive industry. The use of energetic ultraviolet light is emerging as a promising technology to compete with the old methods of surface preparation. This paper reports the utility of using energetic UV light to generate appropriate surface chemical composition on plastics, composites, and metals for subsequent painting or adhesive bonding operations. UV treatments have the potential to ...

Since the late 1990’s, research has been underway in our group at Michigan State University to in... more Since the late 1990’s, research has been underway in our group at Michigan State University to investigate the fabrication of new nano-size carbon material, exfoliated graphite nanoplatelets [xGnP]. The xGnP is fabricated from natural graphite and can be used as nanoreinforcements for polymers as an alternative to expensive carbon-based nanomaterials. Extenisve work in our lab has produced a xGnP around 5-10 nm with a surface area larger than 100 m 2 /g. The diameter (and hence the aspect ratio) can be controlled from sub-micron level to few hundred micrometers. Since graphite is the stiffest material found in nature (Young’s Modulus = 1060 MPa), having a modulus several times that of clay, accompanied with excellent strength, electrical and thermal conductivity, the xGnP should have similar properties to carbon-based nanomaterials, including carbon nanotubes, nanofibers, and fullerenes, yet the estimated cost is far less than these materials. The cost of the graphite nanoplatelets ...

Fibers

Journal of Polymers and the Environment, 2005

Biocomposites from soy based bioplastic and chopped industrial hemp fiber were fabricated using t... more Biocomposites from soy based bioplastic and chopped industrial hemp fiber were fabricated using twin-screw extrusion and injection molding process. Soy based bioplastics were prepared through cooking with plasticizer and blending with biodegradable poly(ester amide). Me- ...