Principal Investigators: Charles Tomasino, leader (Textile Chemistry, NC State), Jerome Cuomo (Materials Engineering, NC State)

Transcription

1 S94-13 Page 1 Annual Report 9/l/94 to 6/30/95 Title: Plasma Treatment - Textiles Code Number: S94-13 Principal Investigators: Charles Tomasino, leader (Textile Chemistry, NC State), Jerome Cuomo (Materials Engineering, NC State) Goal Statement We are developing a fundamental understanding of how different plasmas change the surface characteristics of textile fibers and the wear surfaces of materials used in textile processing and then to characterize the nature of these changes using surface analytical techniques. Longer term, we hope to see how these changes can be exploited for adding value to textile products and help develop pollution free manufacturing processes for their commercial production. Abstract It is known that plasmas can be used to alter material surfaces by removing surface layers, to activate the surface to become polar, to passivate surface making them less polar and to deposit thin films. Plasma treatment of textiles was examined in the 1960 s without much success; however in response to the electronics industrial need, significant developments have been made in plasma tools since then. For example, processes in the 1960 s had lo9 excited particles/cc compared to 1012/cc in the 1990 s. This means there is a great deal more energy available without developing excessively high temperatures. Advances in plasma technology has lead to the development of coatings which increase surface hardness and lower the coefficient of friction of metals. We will assess the usefulness of these recent advances for wear surfaces of material used in textile processing. The project is divided into three tasks focusing on plasma fundamentals for: - Removing surface matter, such as fiber finishes, size, contaminants and the like from fiber surfaces; also the etching of fiber surfaces to reduce fiber diameters. - Activating surfaces to change their polarity. Polar surfaces will be made more non-polar to render them repellent to liquids and reduce adhesion of soil particles, non-polar surfaces will be made more polar to improve water wetting and soil release properties. - Depositing thin films of materials on surfaces to alter their properties. For example diamond-like, ceramic-like or fluorinated surfaces to alter the coefficient of friction and the hardness of wear surfaces and fiber surfaces. National Textile Center Annual Report: August

2 S94-13 Page 2 Relevance to the NTC Mission The Materials Engineering Department at NCSU has established a Plasma Center known as the CAMP-M project under the direction of Dr. Jerome Cuomo. Cuomo, a Distinguished University Professor, comes from IBM Research Laboratories where he was responsible for their Plasma program. He has brought with him seven plasma units and related equipment worth over 3 million dollars. He has actively sought partnership with other departments on campus and, in addition to the NTC funded Textile Program, has ongoing activities with Veterinary Science, the Furniture Program, Physics and Chemistry. He is well known and respected in this field and travels internationally to scientific meetings, National Laboratories, University based Plasma research units, and Industrial manufacturers establishing linkages and partnerships which will ultimately impact the Textile initiative. It is important to note that the NTC funded textile effort is but a small part of the overall NCSU effort, and that these funds arc being well leveraged in fulfilling the NTC mission of improving the Textile Industry s competitiveness by exploring emerging technology. Current Progress The accomplishments of the project thus far include plasma surface modification of several textile substrates, textile size/impurity removal from some common textile products, and the construction of an off-line set-up for measuring tensions and temperature of yarns running over wear surfaces. Descrintion of the Plasma Aunaratus The plasma treatment has been based on an inductively coupled plasma generated over the substrate. The substrate is placed inside the cylindrical plasma chamber in an open rectangular holder which exposes the top side directly to the plasma. The bottom side is also exposed to chamber interior, however the exposure to the excited species which make up the plasma is significantly less. This results in each sample needing to be treated twice, once for each side. The distance from the copper coils which generate the plasma to the surface of the substrate can be varied. The pressure of the gas in the interior of the chamber, and thus the pressure of the plasma, can also be varied. The output power of the plasma and the time the substrate is exposed to the plasma can also be varied. Size Removal from Fiberglass Removing size from woven fiberglass is a convenient starting point for looking at size removal because fiberglass can withstand higher temperatures than organic fibers. Fiberglass requires significantly mot-c energy to discolor or to damage the fibers than it does to discolor or damage other textile products, such as cotton. This latitude offers a wider spectrum of plasma conditions from which to gather information. In addition, fiberglass fabrics are normally heat cleaned to remove the sizing. The major component in the size formulation for fiberglass warps is starch, a common textile size. The work done in this phase was in collaboration with The Research Foundation, State University of New York, Albany. Initial experiments showed that starch size could be removed by an oxygen plasma. Using the iodine spot test for starch, initial probing experiments showed that the blue color was absent from drops placed in the center of the sample but was present at the edges and the area shielded by the sample holder. The initial experiments using the qualitative spot tests showed dependence primarily on time of exposure, power of plasma, 242 National Textile Center Annual Report: August 1995

3 S94-13 Page 3 distance from plasma, and gas pressure in the plasma chamber (or the density of activated oxygen species). Quantitative studies showed that starch size was removed from the fabric surface at almost a linear rate after an initial period of mote rapid size loss. The rates depend primarily on distance to plasma, time of exposure and output power of the plasma. Figure 1 shows the average rate of size removal for a three minute plasma treatment as a function of inductive power for three different pressures (10, 15 and 20 mtorr). The average size removal rate of the fiberglass sample is expressed as the ratio of the factor (mi-mf)/mi and the total plasma treatment time (3 minutes), where mi denotes the mass of the sample prior to the treatment, and mf is its mass after the 3 minute treatment. Further study in this area has also shown that mass loss continues after 3 minutes. This figure shows that the size removal rate increases almost linearly with inductive power for the pressures investigated. Figure 1 (mi-mf)/(mitt) vs. pressure and inductive power r e-.---a 1OmTorr.- c ~.---a 1!imTorr p---q 20mTorr mu E 5 by _ia.;;c._,i A _..- -,/ _,_... 41,/... =r: - /., /...,, ?- 4 /. E,/././ --,:./ _/ & x 3-4-e,,./ /-:,I......:.. : >y ;<... I Inductive Power (W) The effect of pressure on rate of size removal was also examined for several different power levels. Figure 2 below shows the size removal rate as a function of pressure for 5OOW. 1OOOW and 15OOW inductive power. The removal rate depends only weakly on the pressure over the given values. National Textile Center Annual Report: August

4 S94-13 Page 4 Figure 2 (mi-mf)/(mitt) VS pressure Pressure (mtorr) The effect of ion current density on rates rate of size removal was also examined for several different gas pressures. Figure 3 shows the size removal rate as a function of ion current density for 10, 15, and 20 mtorr. For a pressure of 10 mtorr, there is a perfect linear increase of the mass loss %vith current ion density. If the ion current density stays the same but the pressure is increased, a slightly greater normalized mass is observed. Figure 3 (mi-m!)/(mi.t) OS. pressure and ion current density 6 T c.- E 5 CT b Ion Current Density (ma/cm*) 244 National Textile Center Annual Report: August 1995

5 S94-13 Page 5 Direct evidence of removal of size from the fiberglass was obtained by studying treated and untreated fiberglass samples with x-ray photoemission spectroscopy (XPS). In the following, the results are from four different samples: (i) untreated fiberglass; (ii) fiberglass after exposure for 3 minutes to an 02 plasma at 1OOOW inductive power and 15 mtorr of power; (iii) fiberglass after heating at 2OOoC for 20 minutes in air; (iv) sample (iii) after an additional 02 plasma treatment as described under (ii). The trend in the data show that plasma treatment is effective in removing the size from the surface of the fiberglass. XPS measurements were made for carbon, silicon, and oxygen. Figure 4 shows an example of the type of XPS data that was common to the study. The carbon 1s data, shown in figure 4 below, is of all four samples. A large decrease of the carbon 1s signal is seen for all treated fiberglass samples. This shows that each treatment is effective in removing the bulk of the size. A more detailed scan was also preformed for the three treated samples which showed that the highest energy-carbon 1s peak (binding energy greater than 292 ev and due to carbon on the fiberglass) is the smallest for the plasma treated sample. This shows that the plasma treatment is more effective in removing the carbon from fiberglass surface than simple heating or heating followed by plasma treatment. Figure 4 XPS Analysis of C for different sample conditions Healed andtrealed 2u5 295 Blnding Energy ( ev ) Fiberglass is often used for applications in the electronics industry. For these applications small amounts of sodium and aluminum can be a problem. Additional XPS data were taken to look for the presence of these elements. For untreated fiberglass the Na 1s signal is of negligible intensity. After heat cleaning, the Na 1s can be observed. Additional treatment of the sample by then exposing it to the oxygen plasma shows no reduction of the Na 1s peak. However, if the fiberglass is only plasma treated, the Na 1s signal remains negligible. From a contamination point of view(na and Al), the oxygen plasma removal of size is better than simple heat cleaning. Optical emission and mass spectrometric monitoring of size removal have also been performed. These tests also support the above conclusion that oxygen plasma treatment of fiberglass removes the starch size. National Textile Center Annual Report: August

6 s94-13 Page 6 Significant Findings 1). Plasma removal of starch size from fiberglass appears to involve the chemical reactions of excited oxygen species with the hydrocarbon structure of the coating. 2). The plasma desizing can be accomplished in about 30 seconds, and currently is being done with 1000 Watts at 3.0 mtorr of (oxygen) pressure. 3). The volatile components are removed as water and carbon monoxide. 4). The plasma treated fiberglass surface has fewer sodium and aluminum ions than conventional heat cleaned fiberglass. Heat cleaning can take up to four days in an oven which causes sodium, aluminum and calcium ions to migrate to the surface affecting electrical conductivity. Removal of Size from Cotton The parameters for experimentation were similar for cotton as for fiberglass. The qualitative iodine test again indicates that oxygen plasma is highly effective in removing the starch size from the surface (and interstices) of the woven fabric. However, cotton fiber is prone to deterioration during treatment. This deterioration manifests itself as discoloration, loss of fabric mass, and loss of fabric strength (both tensile and tear). The greatest deterioration occurs in those areas where the size is removed the best. Work is continuing in this area directed at finding plasma conditions more conducive for removing the starch without damaging the cotton fiber. Related to this is the gas feed for the plasma itself, mixing oxygen with other gasses, and finding power levels where sufficient breakdown of the starch will allow it to be removed in subsequent bleaching operations. Surface Changes to Polyester Some early experiments were directed at surface activation/deactivation. One of the surfaces that could show a significant difference is polyester. The non-polar surface characteristics of polyester manifest themselves in several ways, including low water takeup. If the surface could be modified to become more polar, the dyeing and finishing procedures could be improved and refined. Two kinds of polyester were used, woven polyester fabric and extruded polyester film (Mylar from DuPont). The fabric was treated with an argon plasma and also with an oxygen plasma. The argon plasma caused slight yellowing with no apparent changes to the hydrophobicity of the fabric. The oxygen also caused a slight discoloration, however the fabric surface was slightly more wetable. Work will continue with these fibers as the removal of sizes other than starch are investigated. Improving Wear Surfaces An off-line set-up to monitor tensions and temperature of wear surfaces of yam traveling over metal and ceramic surfaces has been constructed. This set-up will be used to study the effectiveness of layered plasma deposits on the wear characteristics of yam guides and other wear surfaces. This phase is now at a point where we can start collecting data on various coatings deposited on stainless steel and ceramic guides. We have found a pretreatment process that allows other coatings to aadhereto stainless steel, an important step for the success of this activity. 246 National Textile Center Annual Report: August 1995

7 S94-13 Page 7 Conclusions and Future Plans Plasma removal of textile starch weaving size from fiberglass appears to involve the chemical reactions of excited oxygen species with the hydrocarbon structure of the coating. The plasma desizing can be accomplished in about 30 seconds, and currently is being done with 1000 Watts at 3.0 mtorr of (oxygen) pressure. The volatile components are removed as water and carbon monoxide. Normal heat cleaning of fiberglass, which can take up to four days in an oven, causes sodium, aluminum and calcium ions to migrate to the surface affecting the electrical conductivity. Starch can also be removed from cotton fabrics. Unfortunately, cotton fibers are degraded under some plasma conditions; therefore, milder conditions must be found to optimize this phase. Further study is planned for: - continued work on removal of surface matter, such as fiber finishes, size, contaminants and the like from fiber surfaces; also etching of fiber surfaces to reduce fiber diameters. This work would resemble the work already completed for fiberglass and the work continuing on cotton fabrics. - activating surfaces to change their polarity. Polar surfaces could be made more non-polar to render them repellent to liquids and reduce adhesion of soil particles; non-polar surfaces can be made more polar to improve water wetting and soil release properties. An example of this kind of study is the polyester research already completed. - deposition of thin films of materials on surfaces to alter their properties. For example, diamond-like, ceramic-like or fluorinated surfaces to alter the coefficient of friction and the hardness of wear surfaces and fiber surfaces. - modify the plasma unit with a reel-to-reel transport system that will allow the continuous movement of fabric and yarns through the plasma field. Other Contributors: Research Associates: Paul Vernon, Z. Radzimski (Materials Engineering); Mahmoud Salama (College of Textiles); Collaborator: Gottlieb Oehrlein (State University of New York at Albany); Graduate Student: Cevin Smith (Textile Chemistry, NCSU) National Textile Center Annual Report: August