December 2008

December Meeting
Plastics for Corrosion Protection and Prevention

Technology participants:
• Arkema • Extrusion Plus • TIAero (Brabender) • Blackwell Plastics • Great Western Supply • Ticona • Deep Flex • Southwest Impreglon • Vertec Polymers • Evonik Degussa • Smart Pipe • Western Falcon • Killion Laboratories

***Additional technology participants welcome $50/table. Contact: Jeff Applegate 713 643-6577***


Advancements in polymer technology for Corrosion Protection and Prevention

President’s Message

Happy Holidays!

In the blink of an eye, 2008 will soon be behind us. I hope that many will join in the holiday festivities as we attend the Houston Tidelanders Chorus on December 6th for “The Secret of Christmas”. On Monday, December 8 our Section will be hosting a technical program Plastics for Corrosion Protection and Prevention. I am excited about this program and the opportunity to collaborate with the National Association of Corrosion Engineers as we seek to share new technologies in the plastics industry to provide technical solutions and business opportunities for key industries in our region. We have 15 table top sponsors who will be displaying their technologies. This will be a lunch program and I hope you will encourage all of your associates to make time to attend this great program.

We will kick off the New Year with Killion Laboratories hosting a technical program for all our processors and those interested in a day of hands-on basics in processing polymers. This should be a fantastic program for our membership and student sections. The Polyolefins Committee is hard at work getting prepared for another fantastic Polyolefins Conference in February.

On November 17, I had the opportunity to attend the Education Committee meeting led by Marti Husti. The committee is doing a great job in working with all of the University programs and working to gain student rosters to ensure we keep connected. The Board of Directors and the Education Committee will be launching our effort to join the social networking movement through setting up a Facebook group to interact with our membership and student chapters. This will be a new experience for many of us and I encourage you to try it out. Expect to see it in December.

On behalf of the South Texas section board of directors we wish you and your family a peaceful holiday season!

Jeff Applegate
SPE South Texas President 2008-2009

Plastics Information: Check it Out

Since the Houston Public Library on McKinney St is essentially closed for remodeling, you cannot go there to browse for books on plastics/polymers. However, go to their catalog at www.hpl.lib.tx.us and arrange to pick up books at a branch library.

The Fondren Library at Rice University has the most complete collection of books on plastics and polymers. This is also a prime resource for patent and trademark information, as well as other US Government documents. You cannot check out books there unless you join Fondren Library [$50], but you can arrange for books to be sent to your library by inter-library loan. Use their catalog at http://library.rice.edu/.

The next best place to browse is at the MD Anderson Library at the University of Houston central campus. South Texas Section has donated many plastics books to this library. If you plan ahead, you can get a TexShare library card from a library where you are a member, which will allow you to check out books from any U of H library. Their catalog is at www.library.uh.edu/.

Bulletin Board

Report on TAMU PTIC Consortium Fall 2008 Meeting

by Ananda M. Chatterjee
Education Committee

The Polymer Technology Industrial Consortium (PTIC) meeting was held at Texas A&M University (TAMU) on October 31, 2008. The scribe attended this meeting, together with Don Witenhafer, representing the SPE South Texas section, which is a sponsor and member of PTIC. Other attendees included Total Petrochemical, Huntsman, Ineos polyolefins, Japan Polypropylene Company, Dow Chemical, Mytex Polymers, Sunoco, BASF, Sumitomo, Research Valley etc. Seven presentations were made by TAMU faculty members, covering the research advances by PTIC. The presentations are summarized below.

Prof. Janet Bluemel of Chemistry Department discussed “Inorganic-Organic Hybrid Materials and Olefin Polymerization Catalysts: A Solid-State NMR Study”. Her group is immobilizing homogeneous catalysts on solid supports, in order to improve their lifetime and for other benefits. They have developed a new technique for NMR spectroscopy of suspensions.

Prof. Ozden Ochoa, Mechanical Engineering Department, made her presentation on “Polymer Enhanced Natural and Synthetic Cellular Structures: Proppants to Bone Plates”. She presented processing, morphology, properties and models of walnut shell foam.

Prof. Cris Schwartz of Mechanical Engineering Department discussed his research on the observed role of friction and texture on tactile properties fabrics. Quantitative Descriptive Analysis (QDA) of various fabrics was used to characterize abrasiveness, slipperiness etc. This work potentially can evolve into a haptics consortium at TAMU.

Prof. Dan Davis, Aerospace Engineering, presented his research progress on Advanced Nanocomposites and Applications. Reinforcements for polymers included carbon fiber, fiberglass, and amine-functionalized carbon nanotube. Both matrix-dominated and fiber-dominated failure modes were considered. Tension-tension and tension-compression fatigue studies were presented.

Prof. Donald Darensbourg, Chemistry Department , made his presentation on making polycarbonate plastics by coupling carbon dioxide.with epoxide or oxetane.

Prof. Zhengdong Cheng, Chemical Engineering, discussed “Hydrogel: mechanical oscillation and composites with discotic (disc-like)colloids”. Mechanical oscillation was driven by chemical reaction. For example, Ru⁺³ induced swelling of gel, while Ru⁺² induced shrinking.

Prof. H.-J. Sue, Mechanical Engineering, summarized his group’s studies on the exfoliation of nanoparticles for polymer nanocomposites applications. Zero-dimensional (D), e.g. Zn oxide quantum dots, 1-D (e.g. carbon nanotube) and 2-D (nanoplatelets) nano-structured materials were discussed.

During lunch time a student poster session was presented. PTIC business issues, education matters, industrial needs, short courses etc were covered before the closing. The haptics consortium is still in the discussion stage with potential sponsor companies.

A.M. Chatterjee
Nov 29, 2008

Thank You Letters

		November 4, 2008 Koffi Dagnon 400 Coronado Drive #4 Denton, TX 76209 kld0126@unt.edu
Society of Plastic Engineers (SPE) 14 Fairfield Drive P O Box 403 Brookfield, CT 06804-0403 USA Dear Scholarship Donor, I would like to take this opportunity to sincerely thank the Society of Plastic Engineers for choosing me for 2008-2009 SPE Foundation General Scholarship. I am much honored to be the recipient of this scholarship. It is an honor to be recognized for my hard work, and receiving this scholarship motivates me to continue to strive for excellence. I am in my final year of my doctorate studies and receiving this scholarship allows me to concentrate on my dissertation without having to worry about finances. The SPE Foundation General Scholarship is a clear indication of SPE's commitment for promoting education, knowledge, research and professional achievement. Your generosity has made a profound impact on my life and I am truly grateful to be the recipient of your scholarship. Receiving the 2008-2009 SPE Foundation General Scholarship is of tremendous benefit to me. Thank you again to honor me with this scholarship. Best regards, Koffi Dagnon PhD Student Department of Materials Science and Engineering University of North Texas Denton, TX

Koffi is a graduate student at the University of North Texas working on his Ph.D. in Materials Science. A citizen of Togo, he received his B.S. in Physics-Chemistry at the University of Lome; his M.S. in Physical Chemistry from the University of Marne La Vallee in France; and did advanced graduate study work at the University of Paris 12 before coming to the U.S. For several years, he taught chemistry, physics and math classes at high schools in Togo and France. He serves as Vice President of the SPE Student Chapter at UNT, where he is in charge of open houses for students interested in polymers/plastics. His research work focuses on environmentally degradable plastics, plastics recycling, and biopolymer-based nanocomposites.

Book Bag

	Biodegradable Polymer Blends and Composites From Renewable Resources Long Yu, 2008, 487 pages Price: $125.00 This reference provides a comprehensive, current overview of biopolymeric blends and composites and their applications in various industries. It is organized according to type of blend or composite. The relationship between the structure of the blend or composite and its respective properties is explored, with particular focus on interface, compatibility, mechanical, and thermal properties. By exploring this relationship, the book helps readers design their own materials. In addition to standard techniques, readers learn several innovative, advanced techniques for improving the interfaces between hydrophilic natural polymers and hydrophobic biodegradable polyesters. The book also explains the latest techniques for analyzing and working with biodegradable nanocomposites. Combining fundamental science with applications that either have been commercialized or show great promise for commercialization, this book is ideal for material and polymer scientists and for students who are interested in bringing new environmentally friendly products to market.
	Special Effect Pigments Gerhard Pfaff, 2008, 218 pages Price: $195.00 Color designers, product developers, and application technologists in the coatings, plastics, printing inks, and cosmetics industries, and marketing and salespeople seeking to impart knowledge of coatings and pigments to their customers will find useful information in this book. Readers will learn about properties, manufacturing processes, and specific application areas of special-effect pigments that satisfy the demands of the market. The latest advances in colorimetry ensure that products containing special-effect pigments are subjected to state-of-the-art quality assurance methods.
	Engineering Documentation Control Handbook: Configuration Management for Industry, 3rd Edition By Frank B. Watts, 2009, 376 pages Price: $84.00 Control of engineering documentation, sometimes called “Configuration Management,” is a critical component of world-class manufacturing. The third edition of this popular engineering documentation handbook improves upon one of the best blueprints for efficient EDC/CM ever published, and continues to provide a significant company strategy for managers, project leaders, chief engineers and others. It can be used in many industries to improve the control of engineering documentation. Use the Engineering Documentation Control Handbook to get on track right away and make the release of new products and their documentation flow smoothly and easily. The book is packed with specific methods that can be applied quickly and accurately, to almost any industry and any product, to control documentation, request changes to the product, make those changes, and develop bills of material. The result is a powerful communications bridge between engineering and “the rest of the world” that makes rapid changes in products and documentation possible. With the help of the simple techniques in the handbook, companies can gain and hold their competitive advantages in a world that demands flexibility and quick reflexes–and has no sympathy for delays.

SPE-STX Board Meeting

Location: HESS, Houston, TX
Date: Nov. 10, 2008

An Examination of the Relative Impact of Common Potable Water Disinfectants (Chlorine, Chloramines and Chlorine Dioxide) on Plastic Piping System Components

Sarah Chung, Ken Oliphant, Patrick Vibien and Jingguo Zhang Jana Laboratories Inc., Aurora, Ontario, Canada

Abstract

The three most common disinfectants in potable water are chlorine, chloramines and chlorine dioxide. While these disinfectants are all oxidants, their unique characteristics can result in a significantly different impact on the performance of plumbing system components. In this paper, the chemistry and characteristics of the oxidants are discussed in the context of oxidative degradation of plastic piping system components. Testing strategies to ensure material performance in potable water applications are presented and reviewed.

Introduction

Plastic piping materials have enjoyed a long and successful history. Since the introduction of the first commercial thermoplastic pipe in the 1940’s, plastic pipe usage and applications have continued to expand. In the last 25 to 30 years, plastic piping products have become the predominant piping materials in many markets. As a result of the high demand, the availability and types of plastic piping products have increased significantly [1].

One area of rapid growth for plastic piping products is in the area of hot and cold potable water transport. Due to the durability, resistance to corrosion, installation advantages and overall cost benefits, plastic piping materials have quickly become the material of choice in this market. The acceptance of plastic piping materials has also been facilitated by the proactive approach of the industry in the development of standards to ensure product performance in the application. One area of significant research has been in the development of methodologies to ensure resistance of plastic piping materials to the disinfectants commonly added to potable water to maintain the integrity of the water through the distribution system to end use by the consumer. This paper examines the oxidation mechanisms of plastic piping materials observed in testing to these methodologies for the three common potable water disinfectants: chlorine, chloramines and chlorine dioxide.

Potable Water and Disinfectant Chemistry

Potable water is commonly treated with disinfectants to make it suitable for drinking. Based on the AWWA Water Stats [2], the primary disinfectants added in post-disinfection treatment in the United States are chlorine, chloramines and chlorine dioxide. Chlorine is observed to be the most popular disinfectant followed by chloramines. These disinfectants are relatively strong oxidizers and, even at the relatively low levels used in potable water treatment, have been reported to impact the long-term performance of materials used in potable water [3, 4]. While these disinfectants are all oxidants, their unique characteristics can result in a significantly different impact on the lifetime of materials used in potable water applications.

Table 1 provides a summary of the maximum residualdisinfectant level of the different disinfectants as listed in the EPA Alternative Disinfectants and Oxidants Guidance Manual [5].

Chlorine
Chlorine (Cl₂) is added for disinfection in the form of chlorine gas or a hypochlorite. Chlorine gas dissolves in water. The resulting solutions form an equilibrium between chlorine, hypochlorous acid (HOCl) and the hypochlorite ion (OCl^-) as shown below:

Within the pH range typically observed in potable water applications, the chlorine dissociation reaction is essentially driven to completion to produce hypochlorous acid (HOCl). The hypochlorous acid is the primary disinfecting agent. The hypochlorous dissociation equilibrium is dependent on the pH of the water, with higher pH leading to greater dissociation of the hypochlorous acid and higher levels of the less reactive hypochlorite ion (OCl^-). The aggressiveness of chlorinated potable water is, therefore, a function of both the overall chlorine concentration and the pH of the water. This pH dependency and its impact on performance of plastic piping materials in potable water applications has been described elsewhere [6]. The maximum EPA residual chlorine level is 4 ppm with actual usage levels typically much lower.

Chloramines
Chlorine, in the form of hypochlorous acid, and ammonia are used to produce chloramines (CLA). There are three types of chloramines:

The fraction of each type of chloramines present is dependent on the chlorine to ammonia ratio as well as the pH. Due to taste and odor issues with dichloramine and nitrogen trichloride, monochloramine is typically the prominent species present for chloramines disinfection [5]. The maximum EPA residual chlorine level is 4 ppm withactual usage levels typically much lower.

Chlorine Dioxide
Chlorine dioxide (ClO₂) differs from chlorine and chloramines in that it disinfects by oxidation and it doesnot chlorinate [5]. Chlorine dioxide may be produced many different ways. One method using sodium chlorite (NaClO2) and sodium hypochlorite (NaOCl) is shown below:

Chlorine Dioxide remains a gas dissolved in the water. The maximum EPA residual chlorine level is 0.8 ppm with actual usage levels typically much lower.

The plastic piping industry has been proactive in the development of validation methodologies to ensure the long-term performance of plastic piping materials in potable water applications. This has resulted in the development of several different methodologies.

One test method, ASTM D6284, involves boiling pipe specimens in a flask with chlorine and chloramines. This method provides an indication of the relative resistance of the materials under the test conditions by measuring changes in weight, volume and hardness. It does not, however, provide any specific performance projections under end-use conditions. The methodology has been primarily applied to elastomeric materials.

Three test methods for chlorine resistance testing, ASTM F2023, ASTM F2263 and NSF P71 Protocol have been developed to examine the chlorine resistance of plastic piping materials in potable water applications. These test methods involve testing of plastic piping materials under accelerated conditions (elevated temperature) with extrapolation back to end-use temperatures to provide a benchmark for performance. Specimens are tested in the form of pipe in a pressurized system with a continuous flow of water. The water quality is controlled to maintain a residual disinfectant level that is aggressive yet reflective of the worst case water quality conditions that would be observed in service. Elevated temperatures are used to accelerate and generate failures within a reasonable timeframe. Testing is conducted at multiple temperatures and pressures and fitted with the Rate Process Model to enable extrapolation to end-use conditions. These three methodologies were developed with chlorine treated water as the test fluid. This was done as chlorine is by far the most prevalent disinfectant, is typically observed to be more oxidatively aggressive toward thermoplastic piping materials than chloramines and is typically used at much higher levels than chlorine dioxide, being therefore, directional for any oxidant. There has, however, been recent interest in applying these methodologies to chloramines and chlorine dioxide treated water. As part of a larger research program examining theapplication of these methodologies to chloramines and chlorine dioxide, this paper examines the mechanisms of oxidation observed for the three different oxidants in accelerated testing.

Experimental

A standard commercial 1/2" R-9 PEX tubing meeting the dimensional requirements of the ASTM F876 standard [7] was used for all testing. Disinfectant resistance testing was conducted in general conformance with the ASTM F2023 method with the exception of water quality for the chlorine dioxide and chloramines testing [8]. Water qualities were controlled to obtain a pH of 6.8 and concentration of 4.3 ppm for all three disinfectants (chlorine, chloramines and chlorine dioxide). Fresh Reverse Osmosis water, prepared to the required water quality, is continuously passed through the specimens. Test specimens were internally exposed to continuously flowing test water at two elevated temperatures and constant internal pressure. All of the specimens were tested with ASTM F1807 [9] brass insert fittings. Failure was defined as a loss of fluid through the wall of the pipe.

After testing, the following test methods were performed on the selected tested specimens: Visual examination of the specimens was performed to identify the modes of failure, Oxidation induction time (OIT) was performed in general accordance with ISO 11357-6-2002 (E) [10] at 200°C. Specimens were taken from the inner and outer surfaces as well as from the bulk pipe wall and Micro-attenuated total reflection Fourier Transform Infrared Spectroscopy (micro-ATR) was performed. The inner surface and the fracture surface were examined. Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray analysis (EDX) was performed on the inner surface and the fracture surface.

Results and Discussion

Visual Examination of the Failures
The failure specimens resulting from all three disinfectants appear to have similar failure characteristics. The inner surface of the pipe specimens exhibited a layer of highly degraded and discolored material. Micro-cracking of the inner surface is also visible. Around the point of failure, the micro-cracks appear to have coalesced into large cracks in the axial direction parallel to the axis of the specimen. Sectioning of the wall reveals that the micro-cracks have propagated radially beyond the highly degraded layer into the bulk of the wall forming fissures. The surfaces of the fissures show signs of oxidation. The area localized around the failure point exhibits many deep cracks and typically one or more fissures that have visibly expanded. Failure is observed as a single fissure penetrating through the wall leading to a brittle slit or pinhole and to the loss of test fluid. The point of failure was typically near the inlet fitting (area of highest flow turbulence). The failures for all three oxidants appear to be typical of Stage III brittle oxidative failures.

Chlorine Dioxide Exposed Specimens
Figure 1a shows the inner surface degradation and cracking observed by SEM for the chlorine dioxide tested specimen. In Figure 2a, a cross-section of the failure crack is shown. Cracking and degradation, consistent with brittle oxidation, is observed through the pipe wall. The degradation level is observed to be highest at the inner exposed pipe surface and decreases through the pipe wall. Rupture of the final section of the wall appears to have occurred through a ductile or fast fracture type of mechanism and does not show the characteristics of degradation observed in the inner and mid pipe wall. Oxygen (as observed by EDX (Table 2)) is present through the specimen wall, indicating oxidation of the specimen through the fracture surface. EDX analysis also reveals trace levels of chlorine near the inner surface. The presence of the carbonyl peak, observed by the peak in the region of 1812 to 1660 cm-1 by FTIR, provides further evidence of oxidation of the inner pipe surface. A significant overall depletion in the stabilizer, as indicated by the significant decrease in the OIT values in Table 2, is also observed through the entire specimen. Overall, oxidative degradation are highest at the inner exposed surface decreasing through the pipe wall.

Similar analysis of samples exposed for different exposure periods shorter than ultimate failure suggests that the overall failure mechanism is: depletion of stabilizers at the inner pipe surface, oxidation of the inner layer, micro-cracking of the inner layer, crack propagation through the wall with oxidation in advance of the crack front and final rupture of the remaining ligament thickness resulting in ultimate failure.

Chloramines Exposed Specimens
Extensive degradation and flaking of the inner surface of the chloramines exposed specimen is observed in the SEM of Figure 1b. Similar to the chlorine dioxide exposed specimen, the cross-section of the failure crack, as shown in Figure 2b, is observed to have cracking and degradation consistent with brittle oxidation. The observed degradation is heaviest at the inner pipe surface and decreases through the specimen. Rupture of the final section of the wall appears to have occurred through a ductile or fast fracture type of mechanism and does not show the characteristics of degradation observed in the inner and mid pipe wall. EDX reveals oxygen through the specimen wall with only a trace level of chlorine in the mid wall. Oxidation, as observed by the presence of carbonyl peaks by FTIR, is observed to be present from the inner to the mid pipe wall. No significant degradation is observed near the outer wall (confirming rupture of the final ligament thickness through non-oxidative mechanisms). Significant depletion of the stabilizer, as observed by the low OIT values in Table 2, is observed through the entire pipe wall.

Similar analysis of samples exposed for different exposure periods shorter than ultimate failure suggests that the overall failure mechanism is: depletion of stabilizers at the inner pipe surface, oxidation of the inner layer, micro-cracking of the inner layer, crack propagation through the wall with oxidation in advance of the crack front and final rupture of the remaining ligament thickness resulting in ultimate failure.

Chlorine Exposed Specimens
As shown in Figure 1c, extensive micro-cracking of the inner surface is observed for the chlorine exposed specimen. The fracture surface (Figure 2c) shows cracking and degradation consistent with oxidative degradation. EDX analysis reveals that Oxygen is present through the entire specimen wall. Chlorine is observed in the inner and mid walls (Table 2), consistent with chlorine substitution on the PEX backbone. The levels observed are noticeably higher than the trace levels observed for the chlorine dioxide and chloramines tested specimens. Oxidation is observed through the entire specimen wall thickness, with a lower level of oxidation near the outer surface, as indicated by the presence of the carbonyl peaks by FTIR. The OIT values in Table 2 indicate significant stabilizer depletion through the entire specimen wall thickness.

Similar analysis of samples exposed for different exposure periods shorter than ultimate failure suggests that the overall failure mechanism is: depletion of stabilizers at the inner pipe surface, oxidation of the inner layer, micro-cracking of the inner layer, crack propagation through the wall with oxidation in advance of the crack front and final rupture of the remaining ligament thickness resulting in ultimate failure.

A Comparison between Disinfectants

Based on the analysis conducted, the microscopic oxidation and degradation mechanisms observed for the three different disinfectants look similar. Degradation and cracking are observed on the inner surface and cracking consistent with brittle oxidation is observed through the majority of the specimen wall. The portion near the outer wall of the failure points are observed to exhibit little oxidation and appear to be more consistent with a fast ductile failure which may have occurred once the wall thickness was too thin to withstand the internal test pressure. Both the presence of oxygen observed in the EDX analysis and the presence of carbonyl peaks in the FTIR analysis provide clear evidence that oxidation has occurred. Significant depletion of the stabilizer is observed in all three disinfectants as observed by the OIT values.

The consistency observed in the failure mechanism for the different oxidants suggests that the methodologies developed for chlorine resistance testing can also be applied to analysis of the impact of chloramines and chlorine dioxide on pipe performance.

While the macroscopic mechanisms observed appear similar between the different oxidants, the overall aggressiveness of the oxidants at the test conditions is observed to vary noticeably. Relative test lifetimes for the three different oxidants at the test conditions vary by a factor of three. While some of this difference can be explained based on the relative oxidative aggressiveness of the different oxidants, the relative test lifetimes suggest that other more subtle mechanisms may be at play.

One potential difference may be due to the physical nature of chlorine dioxide compared to chlorine and chloramines. Chlorine and chloramines, as liquids, can only consume stabilizers in the area which is in direct contact with the liquid. As chlorine dioxide is a dissolved gas in solution, it has the potential to diffuse into the bulk polymer and as a result, may consume stabilizers not only in the area with direct contact to the solution but also in areas of the bulk wall where diffusion of chlorine dioxide molecules has occurred. Table 3 provides a comparison of OIT values of a sample pipe that was exposed to chlorine and chlorine dioxide. With both disinfectants, a significant decrease in the OIT values is observed with exposure. The OIT values with chlorine dioxide exposure are similar to or slightly lower than with chlorine exposure. However, the exposure period with chlorine dioxide is approximately 40% of the chlorine exposure period showing that chlorine dioxide appears to deplete the stabilizer at a much quicker rate than chlorine. Models of diffusion of chlorine dioxide have been explored by X. Colin et al. [11].

Additional research is underway to further characterize the specific mechanisms for the different oxidants and confirm the applicability of the standard test methodologies in assessing resistance to chloramines and chlorine dioxide.

Conclusions

Based on the analysis conducted, the microscopic oxidation and degradation mechanisms observed for the three different disinfectants look similar. The consistency observed in the failure mechanism for the different oxidants suggests that the methodologies developed for chlorine resistance testing can also be applied to analysis of the impact of chloramines and chlorine dioxide on pipe performance. While the macroscopic mechanisms observed appear similar between the different oxidants, the overall aggressiveness of the oxidants at the test conditions is observed to vary noticeably. Additional research is underway to further characterize the specific mechanisms for the different oxidants and confirm the applicability of the standard test methodologies in assessing resistance to chloramines and chlorine dioxide.

Acknowledgements

This work was supported by the Plastic Pipe Institute High Temperature Division and the National Research Council of Canada.

References

1. D. A. Willoughby, et al., Plastic Piping Handbook, McGraw-Hill, New York (2002).
2. The Water Utility Database 1996 Survey, American Water Works Association (2000).
3. S. Reiber, Chloramine Effects on Distribution System Materials, AWWA Research Foundation (1993).
4. Z. Zhou, X.Niu, A. Chudnovsky, S.S. Stivala, Proceedings of the Third International Symposium on Risk, Economy and Safety, Failure Minimization and Analysis, R.K. Penny ed., Pilanesberg, South Africa (July 1998).
5. USEPA, Alternate Disinfectants and Oxidants Guidance Manual. EPA 815-R99-014, Office of Water (April 1999).
6. S. Chung, J. Couch, J.D. Kim, K. Oliphant and P. Vibien, Environmental Factors In Performance Forecasting of Plastic Piping Materials, ANTEC, Nashville (2003).
7. ASTM F876 Standard Specification for Crosslinked Polyethylene (PEX) Tubing, ASTM International, USA (2005).
8. ASTM F2023 Standard Test Method for Evaluating the Oxidation Resistance of Crosslinked Polyethylene (PEX) Tubing and Systems to Hot Chlorinated Water, ASTM International, USA (2005).
9. ASTM F1807 Standard Specification for Metal Insert Fittings Utilizing a Copper Crimp Ring for SDR9 Cross-Linked Polyethylene (PEX) Tubing, ASTM International, USA (2005).
10. ISO 11357-6 Differential Scanning Calorimetry (DSC) – Part 6: Determination of Oxidation Induction Time, ISO, Switzerland (2002).
11. 11. X. Colin, L. Audouin, J. Verdu, M. Rozental-Evesque, F. Martin and F. Bourgine, Kinetic Modeling of the Aging of Polyethylene Pipes for the Transport of Water Containing Disinfectants, PPXIII, Washington D.C. (2006).