|M.Sc Student||Ronen Avner|
|Subject||Electrospinning of Ultra High Molecular Weight Polyethylene|
|Department||Department of Chemical Engineering||Supervisors||Professor Yachin Cohen|
|Dr. Dmitry Rein|
|Full Thesis text|
In the last half century, as weapons and projectiles have evolved, there is an increase demand for improved protective clothing; heavy body armor does not give sufficient answers to the growing need for light weight, flexible and strong body armor. Scientists and engineers have developed light weighted fiber based armor (Kevlar ®, Dyneema ® etc.). Recent interest is in ultra high molecular weight polyethylene (UHMPWE) fibers which show enhanced physical properties and unique energy absorption. These fibers go through several drawing process and assumed to be composed of ideal fully extended chains in a highly crystalline state.
The relationship between fibers diameter and physical properties has been studied and it has been shown that Young modulus increases with fibers diameter decrease. Therefore, the overall goal of our study was to fabricate UHMWPE nano fibers with enhanced physical properties, presumably by creating oriented extended chains during the spinning process itself.
Fabrication of the nano fibers was accomplished by using a novel apparatus based on the electrospinning (ES) process; ES uses electric tension to fabricate polymeric nano fibers. In our study we had to apply high voltage on a very low conductive and non polar solution. Temperature dependence was also a significant factor in the process. Two solvents were used to dissolve the UHMWPE powder and apply electrical conductivity to the solution. A unique low mass heated air flow apparatus was used to provide sufficient condition and prevent phase separation. Collected fibers were characterized by using electron microscopy and XRD, physical properties were measured at initial conditions and after hot and cold drawing.
Influencing factors on the ES process were studies. The influence of the ratio between the two solvents was tested. It seems that solvents ratio influences electrical conductivity of the polymer solution and therefore influences the fiber diameter and physical properties.
Contrary to the commercial Dyneema ® fiber which has a large diameter (~ 3000 nm), UHMWPE nano fiber were electrospun at a diameter of ~500 nm and less. Physical properties show increased properties as electrical conductivity of the solution increases. Partly orientation of the electrospun fiber was accomplished during the ES process and the formation of the fiber, drawing after treatment was still in need.