Permeation behavior of water and acid solution vapor into undegradable polymer

BÀI BÁO KHOA HỌC DOI:10.36335/VNJHM.2019(EME2).164-173<br /> <br /> <br /> PERMEATION BEHAVIOR OF WATER AND ACID SOLU-<br /> TION/VAPOR INTO UNDEGRADABLE POLYMER<br /> Dinh Van Chau1<br /> <br /> Abstract: Corrosion can be controlled by isolation of the metal from the corrosive environment.<br /> Isolation of corrodible metals from corrosive environments is probably the most general method of<br /> the corrosion protection afforded by paint films, sealers and lining on base materials. Fluoropoly-<br /> mers provide superior chemical resistance and are used in a variety of markets. These polymers are<br /> widely used to seal and isolate materials, especially under harsh conditions, in the chemical process<br /> industries and in the semi conductor, pharmaceutical, and biotechnology industries, where con-<br /> tamination may be critical. This study investigated the phenomenon of permeation only into the flu-<br /> oropolymers materials lining under corrosive environment. Permeation behavior of water and acid<br /> solution or vapor into undegradable polymer is studied and explained. The weight changes gener-<br /> ally increase with the increase of temperatures. Relatively rapid diffusion rate of water in the fluo-<br /> ropolymers sheets were observed from these results. Ethylene tetrafluoroethylene (ETFE) sheet<br /> absorbed less water but has the biggest diffusion coefficient than other fluoropolymers in this re-<br /> search. The highest weight uptake is obtained for PFA sheet immersion. The transport of water vapor<br /> is considered the same as water solution. In other words, they might move in the same phase. Weight<br /> changes could be plotted against square root time following Fickian diffusion type. Activation en-<br /> ergy of water diffusion in fluoropolymer in liquid phase is higher than in vapor phase. The weight<br /> of fluoropolymers sheets could be recovered to the initial weight after dried at 50oC for four days.<br /> Keywords: Polymer lining, permeation, anticorrosion.<br /> Received: December 11, 2019 Accepted: December 12, 2019 Published on: December 20, 2019<br /> <br /> 1. Introduction in determining whether it is more advantageous<br /> Isolation of corrodible metals from corrosive to line a base material or to select an appropriate<br /> environments is the most general method of the corrosion resistant alloy as the base metal for<br /> anticorrosion afforded by paint film, sealers and construction. When high temperatures and high<br /> lining on base materials. The material for lining concentrations of chemicals rule out a lining sys-<br /> is defined as physical materials used to protected tem, or when downtime for repairing of a lining<br /> or covered an inside surface. Lining are barrier is unacceptable, the high alloy is frequently se-<br /> applications used to protect base materials such lected [1-5].<br /> as carbon steel, concrete, or other substrates Although many corrosion-resistant metals<br /> from corrosive environment. Effective isolation and alloys are available, they do not always rep-<br /> requires that polymeric materials have good bar- resent the most practical or economical means to<br /> rier properties and remain adherent in the pres- prevent corrosion. In many situations it is better<br /> ence of water, chemicals, gas, vapor and the to selected a less resistant metal and provide<br /> products of metallic corrosion. Generally, lining some types of lining to protect it from corrosion.<br /> has a low coefficient of friction and provide an Lining may be made of plastic sheet, glass, or<br /> easily cleanable surface. Economics play a part cement, or can be applied in liquid form [6-8].<br /> <br /> 1<br /> University of Engineering and Technology, Vietnam National University at Hanoi<br /> Email: chaudv@moit.gov.vn<br /> TẠP CHÍ KHÍ TƯỢNG THỦY VĂN<br /> 164 Số phục vụ Hội thảo chuyên đề<br />  RESEARCH ARTICLE<br /> <br /> <br /> Polymeric lining performs two important late on the bond interface of lining-metal system.<br /> functions in metal equipment. First, it protects The combination of permeation and lining degra-<br /> the equipment from deterioration by the corro- dation will reduce the life time of lining as a con-<br /> sive and erosive action of chemicals and, second, sequence of increasing of permeation rate of<br /> it protects the quality of the product. The use of chemicals and corrosion rate of substrate.<br /> polymeric lining is the most common and eco- Many lining failures are caused by the per-<br /> nomical means to protect base materials against meation of environmental solution or vapor that<br /> corrosion. In general, good corrosion protection result to the blisters and lining delamination. In<br /> requires the establishment of good lining adhe- some cases, environment solution or gas/vapor<br /> sion. To exhibit high performance ability for lin- reacts with polymer lining or base materials to<br /> ing, adhesion must be maintained under the form corrosion product and make the lining to<br /> presence of water, electrolyte, and various prod- be failure. The failure of lining will cause the de-<br /> ucts of the corrosion reactions [9-10] struction of base materials and leakage which<br /> For many years vessels or equipments have may represent a serious hazard to personnel [13].<br /> been successfully lined with various type of In addition, the failure of lining part or the de-<br /> coating or lining material. Many vessels have struction of base materials will contaminate the<br /> given over 20 years of reliable service. However, product.<br /> there are occasionally reports of lining failures Permeation is defined as the process by which<br /> that can be traced. Inadequate surface prepara- a chemical move through a material on a molec-<br /> tion, thermal stresses, permeation, debonding ular level [14]. The three steps process includes:<br /> and operation condition are found to be the main - Absorption: Chemical is absorbed into the<br /> problems in lining failure, especially permeation outer surface of a material.<br /> of solution and vapor. In order that lining should - Diffusion: Chemical then diffuses through<br /> offer protection from corrosion, it should with- the material on a molecular level.<br /> stand to one or other of the processes of blister- - Desorption: Chemical emerges on the inside<br /> ing/delamination and corrosion reactions. This surface of the material.<br /> was considered by Mayne [11], who determined On other hand, penetration is defined as the<br /> that the permeability of organic coatings to both physical transport of a chemical from one side<br /> water and oxygen is so high that the rate at which of the material to the other side of the material,<br /> they arrive at the interface of the coating and such as through imperfections, holes, tears, etc<br /> steel is greater than that required for corrosion to [15]. All materials are somewhat permeable to<br /> proceed. Water at the organic coating/substrate chemical molecules, but plastic materials tend to<br /> interface is often the main cause of degradation be an order of magnitude greater in their perme-<br /> of organic coating systems. Kamal and Saxon ability rate. Gases, vapor, or liquids will perme-<br /> [12] claimed that water has at least three kinds of ate polymers. Factors effecting permeation are<br /> effects in the degradation of polymers. One is concentration of the solute, temperature of the<br /> chemical effect: hydrolysis of the ester or amide media, time of exposure and liner thickness.<br /> bonds. The second is physical effect: loss of the Thermoplastic fluoropolymers play a key role<br /> bond between the coating and substrate. The in materials integrity management by protecting<br /> third is photochemical effect: generation of hy- the high purity materials during transport, pro-<br /> droxyl radicals or other chemical species which cessing and storage. Fluoropolymers provide su-<br /> may react with polymers. perior chemical resistance and used in a variety<br /> Chemicals other than water can also permeate of markets. These polymers are widely used to<br /> in and degrade a lining which it affects perform- seal and isolate materials, especially under harsh<br /> ance. Moreover, this chemical also can accumu- conditions, in the chemical process industries<br /> <br /> TẠP CHÍ KHÍ TƯỢNG THỦY VĂN<br /> Số phục vụ Hội thảo chuyên đề 165<br />  RESEARCH ARTICLE<br /> <br /> <br /> and in the semi conductor, pharmaceutical, and<br /> biotechnology industries, where contamination<br /> may be critical.<br /> Fluoropolymers are often chosen for corro-<br /> sive services due to their relative cost position<br /> compared with high alloy materials and due to<br /> their availability. Fluoropolymers products af-<br /> ford excellent chemical resistance towards ag-<br /> gressive solution. However, one of the downfalls<br /> of these materials is that certain chemicals in liq-<br /> uid and gas phase can permeate and reach the<br /> base metal components causing product failure.<br />
<br /> Permeation is an important factor in deter- Fig. 1. Chemical structure of ETFE, FEP and<br /> mining the suitability of a particular polymer for<br /> PFA<br /> specific applications such as protective coatings, Table 1 shows the properties of these fluo-<br /> packaging materials, selective separations, bio- ropolymers. Before permeation test, specimens<br /> medical devices, etc. Understanding the mecha- were dried in drying oven at 50oC for at least 100<br /> nisms of permeation can help in the selection of hours. Permeation test in liquid and vapor phase<br /> materials, as well as in product or process de- were done for sheets at different temperatures<br /> velopment. Permeation is affected by several and concentrations. Fluoropolymer sheets test<br /> factors such as concentration of the solution, were examined with simple immersion test in<br /> temperature of solution and time of exposure. In order to measure the diffusivity and characteris-<br /> this work, the effects of these factors on perme- tic of fluoropolymers.<br /> ation characteristic of corrosive environment are<br /> discussed. Table 1. Engineering thermoplastic fluoropoly-<br /> mers generally used for lining<br /> 2. Experimentals<br /> 
<br /> The evaluation of fluoropolymers sheets and #  <br /> <br /> <br />


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(=FEP>ETFE. As for<br /> the case of water immersion, the change in<br /> weight gain is found to be almost similar for both<br /> solution and vapor phase, only PFA reveals a<br /> small difference between the weight change for<br /> acid solution and for acid vapor. Even though,<br /> ETFE shows the lowest saturation value it has<br /> the highest diffusion coefficient as calculated by<br /> the same method already described in the case<br /> of water immersion.<br /> Table 4 highlights the diffusion coefficient of<br /> acid in fluoropolymers at different temperatures,<br /> it is observed an alike behavior for the three<br /> polymer that is a drastic decrease in the diffusion<br /> coefficient as temperature decrease; the highest<br /> values of the diffusion coefficient are obtained<br /> for liquid solution as compared to vapor phase.<br /> Table 4. Diffusion coefficients of 35<br /> mass% HCl in fluoropolymers at different<br /> temperatures<br />
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