EFFECT OF BETA-NUCLEATION ON AGING AND CRACK GROWTH RESISTANCE OF POLYPROPYLENE EXPOSED TO CHLORINATED WATER

Papers # 2018 Las-Vegas

This research addresses the effect of nucleation on the global aging behavior and the fatigue crack growth (FCG) resistance of commercial alpha- and beta-nucleated polypropylene random copolymer pipe grades (PP-R) when exposed to chlorinated water (5 mg/l free chlorine) at an elevated temperature of 60°C. Comparing the two PP-R grades, for the alpha-nucleated PP-R a significantly higher embrittlement due to exposure to hot chlorinated water was obtained in tensile tests with micro-sized specimens. In the FCG experiments with cracked round bar specimens, the beta-nucleated PP-R also outperforms the alpha-nucleated type in non-chlorinated water. Experiments with PP-beta in chlorinated water revealed a significantly reduced FCG resistance, most likely caused by enhanced local crack tip aging.

In many world regions, water is polluted with bacteria, viruses and parasites, and disinfection of contaminated water is required as a prevention of waterborne diseases. Chlorine is the most widely utilized and the most affordable water disinfectant, as it is easy to use and highly efficient against different kinds of waterborne pathogens. In this context, it is well known that polyolefins in general exhibit a significant degree of aging when exposed to water disinfectants. However, for the case of polypropylene (PP), little information is available on how the aging behavior and crack growth resistance in chlorinated water environments is affected by the material morphology. Hence, the aging behavior and crack growth resistance of two commercial PP random copolymer pipe grades was systematically investigated. One of the PP grades was of a conventional alpha-nucleated type (PP-alpha), whereas the other was specifically beta-nucleated (PPbeta). Material exposure and testing was performed at an elevated temperature of 60°C, and under environmental conditions of non-chlorinated and chlorinated water, the latter containing 5 mg/l chlorine. In addition to global aging and fatigue crack growth (FCG) experiments, tensile tests and DSC experiments were conducted. While for the microsized specimens of PP-alpha the exposure to chlorinated water at 60°C resulted in significant embrittlement after 1000 h, beta-nucleated PP-R exhibited a high resistance to chlorinated water exposure. In the FCG experiments, PP-beta turned out to be superior to PP-alpha under non-chlorinated water environment. Furthermore, in chlorinated water crack growth rates for PP-beta were found to be higher than in non-chlorinated water.

Related keywords : nucleation effects; aging; fatigue crack growth resistance; polypropylene pipe grades; chlorinated water.
Please note that the whole article content is available on PPCA website onlySource : 2018 Las-Vegas


Related papers

CHARACTERIZATION OF POST-USE POLYETHYLENE AND POLYPROPYLENE RECYCLATE BLENDS FOR PIPE APPLICATIONS

Author(s) : Markus Gall, Reinhold W. Lang, Joerg Fischer, Ansgar Niehoff, Steven Schmidt 2018 Las-Vegas

Despite recent efforts in promoting the utilization of recycled polymeric materials for more diverse and more advanced applications, there are still significant knowledge gaps with regards to the applicability of certain recyclate types for specific “re-use” purposes. When it comes to pipe applications, for...

FATIGUE CRACK GROWTH TESTING IN CHLORINATED WATER AT ELEVATED TEMPERATURES - TEST EQUIPMENT AND TEST PROCEDURE

Author(s) : Joerg Fischer, Patrick R. Bradler, Reinhold W. Lang 2018 Las-Vegas

In the present paper, a novel test system for conducting fatigue crack growth (FCG) experiments under superimposed mechanical-environmental conditions is presented. FCG experiments were performed on a polypropylene (PP) grade and a short-glass fiber reinforced polyamide 66 (PA-GF) grade as model materials. The...

A NOVEL PROCEDURE FOR CHARACTERIZING FATIGUE CRACK GROWTH IN CRB SPECIMENS VIA AN OPTICAL TECHNIQUE

Author(s) : Joerg Fischer, Paul J. Freudenthaler, Patrick R. Bradler, Reinhold W. Lang 2016 Berlin

Cyclic tests with cracked round bar (CRB) specimens have been used for some time to characterize the slow crack growth behavior of polyolefin pipe grade materials. In fact, most recently a standardized test procedure for cyclic CRB testing has been released in ISO 18489. To obtain kinetic data for cyclic crack growth...

FATIGUE CRACK GROWTH RESISTANCE OF POLYPROPYLENE IN CHLORINATED WATER AT DIFFERENT TEMPERATURES

Author(s) : Joerg Fischer, Patrick R. Bradler, Reinhold W. Lang, Gernot M. Wallner 2016 Berlin

The present paper aims to study the crack growth resistance of a black-pigmented polypropylene pipe grade when exposed to elevated temperatures and various environmental media (air, deionized water, ionized water with a specific chloride content, and chlorinated water) under the simultaneous application of cyclic...

QUALITY AND PERFORMANCE ASSESSMENT OF IN-PLANT AND POST-USE PE RECYCLATES FOR PIPE APPLICATIONS

Author(s) : Reinhold W. Lang, Patrick R. Bradler, Joerg Fischer, Dominik Poehlmann, Steven Schmidt, Ansgar Niehoff 2016 Berlin

In the present paper, a highly effective test and characterization concept for polymer recyclate materials is proposed and validated. Based on the proposed methods, a study was carried out to investigate the potential of in-plant and post-use PE recyclates from various applications to be utilized in PE recyclate...

STRAIN HARDENING MODULUS: A MEASURE FOR RANKING TIME TO FAILURE OF RANDOM POLYPROPYLENE PIPE MATERIALS

Author(s) : Rieky Steenbakkers, Linda Havermans, Patrick Voets, Jonathan Rabiei, Rudy Deblieck 2016 Berlin

The resistance to Slow Crack Growth of HDPE is related to the strain hardening modulus as determined from a tensile test at 80 °C. Correlatio ns between traditional methods (e.g. Full Notched Creep Test, Notched Pipe Test) and other accelerated tests (e.g. fatigue testing) show that the same failure mechanism is...

Total overview of developments in PVC-O in size and couplers.

Author(s) : Paul van Doesburg, Berend Stel, Rob Spekreijse 2016 Berlin

PVC-O is the accepted pipe solution for the future. Worldwide, more and more countries go in the direction of PVC-O. The main applications for PVC-O at this moment are potable water, wastewater, irrigation and gas. PVC-O is produced for many years from the 80’s until 2007 the sizes were in majority small (mainly...

A Risk Based Approach to Prioritizing Aldyl Piping Replacements in Gas Distribution Systems

Author(s) : Dr. Ken Oliphant, William Luff, Dr. Peter Angelo, Patrick Vibien 2014 Chicago

Managing aging pipeline infrastructure is an important part of overall pipeline risk management. The critical risk management questions for an aging infrastructure are: how quickly should replacement occur and what parts of the system should be prioritized for replacement. To answer these questions it is necessary to...

An Assessment of the Approach to Validate Polyethylene Pipe in Potable Water Systems

Author(s) : Dr. Ken Oliphant, Patrick Vibien, Dr. Michael Conrad, Sarah Chung 2014 Chicago

A new methodology has been developed to validate the performance of polyethylene piping materials in potable water applications. The methodology is based on several research programs which examined a standardized accelerated test methodology (ASTM F2263 Standard Test Method for Evaluating the Oxidative Resistance of...

Evolution of Piping Systems-A Brief History of Innovation

Author(s) : Riccardo Barbone, Georg Fischer 2014 Chicago

This short paper reviews the major milestones in the history of piping systems. A special emphasis is given to the sources and reasons for innovation. Starting with nature as a basis and discovering the basic laws of hydraulics, man has been driven to innovate by emulating nature. The political and social forces that...

Members of the Association

BOREALISBOROUGEINEOS O&PIRPCKorea Petrochemical IND. Co., LTDLyondellBasellPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE
TOP