Surface Modification Of Ultrahigh Molecular Weight Polyethylene Fibers By Atmospheric Pressure Pulsed-Radio-Frequency Plasma

The main objective of this thesis is to use the self-developed atmospheric pressure pulse radio frequency (RF) plasma equipment to provide highly efficient surface modification for ultrahigh molecular weight polyethylene (UHMWPE) fibers. Discharge properties of the plasma, etching effects surface wettability, interface bonding, chemical structure as well as stretching strength of UHMWPE fibers have been investigated. Ultraviolet pretreatment has been introduced into the process to shorten the plasma treatment time and improve the industrial feasibility, The modification mechanism has also been analyzed.Firstly, through the electrical and optical emission spectrum analysis in different discharge power, modulated pulse frequency and duty cycles, carrier gas flow ratio, we discussed the plasma discharge properties. The peak-peak current increases with its peak-peak voltage, showing a uniform a discharge mode. When 250 W power was supplied, the discharge space between the electrodes was full of uniform discharge. When the duty cycle was more than 80%, discharge current was reduced to 0.55 A.; Plasma emission spectra with 1.5% O2 in the carrier gas showed that some high-energy active particle such as OH, O, O2+, N2+ existed in the plasma and the particle concentration increased with the with the discharge power.Secondly, we treated the UHMWPE fibers by use of the atmospheric pressure pulsed-RF plasma to improve the bonding properties of the fibers to the composite resin. Through the SEM, monofilament climb test, FTIR, pull out test of single fiber, the modified surface property of the fiber was discussed. The SEM results showed that, with the increase of the pulse RF plasma processing time, fiber surface etching effect improved. The surface micro indentation and deepen pit structure become dense. Oxygen introduction into the discharge improved the etching effects. Hydrophilicity of the fiber surface was improved with the increase of the processing time. After 120 min, the climbing height of methylene blue solution through UHMWPE monofiber is 8.5 mm, increasing 3.7% compared with the untreated UHMWPE fiber. Through the infrared spectrum, it is found that oxygen active functional groups such as COO, OH can be introduced into the fiber surface. At the discharge conditions of 1.5% O2, modulation frequency 10000 Hz, duty cycle 80% empty, discharge power 250 W, processing time 5 s, the IFSS was improved 2.5 times at the breaking strength loss of 1.38%.Finally, in order to decrease the plasma treatment time and improve the industrial feasibility of this atmospheric pressure pulsed RF plasma surface modification methods, ultraviolet irradiation pretreatment is applied. The modified UHMWPE fiber was also characterized by SEM, monofilament climb test, FTIR, pull out test etc... The results show that 20 min pretreatment of 325 nm ultraviolet irradiation, can improve IFSS by 2.7 times at the processing time of 3 s,1.5% O2, modulation frequency 10000 Hz, duty cycle 80%, discharge power 250 W, and the breaking strength is only decreased by 3.85%.To sum up, a uniform discharge with lowered discharge current is obtained by atmospheric pressure pulsed RF plasma discharge. Combined with UV irradiation pretreatment, the IFSS of the UHMWPE fibers can be improve by 2.7 times at the plasma processing time of 3 s. The improvement of IFSS is attributed to the micro indentation and deepen pit structure and oxygen group introduction into the fiber surface. This research result will be helpful for the industrial application of this technology.