Studying the Degradation of Three Polymers under Different Chlorine Concentrations and Exposure Times

Abstract

Due to chlorine's ability to kill bacteria and fungi through a chemical reaction, chlorine solutions are commonly used to clean and disinfect numerous public facilities, although these actions are also dependent to the equipment present in those facilities. Accordingly, the interest in studying its effect when in contact with different materials is obvious. This study was carried out through accelerated degradation tests and various analysis methods (optical microscope, scanning electron microscope, and tensile tests). The objective was to observe the wear presented by three polymeric materials, polyvinyl chloride (PVC), high-density polyethylene (HDPE), and polypropylene (PP), when exposed to chlorine's action in swimming pools and drinking water treatment plants. The resulting effect depends on the chlorine content and the type of contact between the chemical agent and the material. The aim was to select the material less likely to be affected by chlorine through tests and analyses, allowing a longer component life. The use of certain more resistant polymeric materials can drastically reduce maintenance, reducing fundamental factors such as costs, the downtime of municipal facilities, and also the risk to public health. It was concluded that PVC has the most stable behaviour overall when in contact with chlorine solutions.

Keywords: HDPE; PP; PVC; chlorine action; municipal facilities; polymeric degradation; polymers.

Figure A1

EDS of the red zone in the second image of the PVC sample.

Figure A2

EDS of the red zone in the second image of the HDPE sample.

Figure A3

EDS of the second image of the PP sample.

Figure 1

PVC (A), HPDE (B), and PP (C) visual inspection after 3 weeks of immersion in 100% NaClO.

Figure 2

Mass variation recorded after three weeks for all samples.

Figure 3

Mass variation recorded after three months for all samples.

Figure 4

OM images of the PVC (A), HPDE (B), and PP (C) samples not immersed in NaClO concentration at 100× magnification.

Figure 5

OM images of the PVC samples submitted to accelerated degradation at 100× magnification ((A)—sample submitted to 2% NaClO concentration for three weeks; (B)—sample submitted to 100% NaClO concentration for three weeks; (C)—sample submitted to 2% NaClO concentration for three months; (D)—sample submitted to 100% NaClO concentration for three months).

Figure 6

OM images of the HDPE samples submitted to accelerated degradation at 100× magnification ((A)—sample submitted to a concentration of 2% NaClO for three weeks; (B)—sample submitted to a concentration of 100% NaClO for three weeks; (C)—sample submitted to a concentration of 2% NaClO for three months; (D)—sample submitted to a concentration of 100% NaClO for three months).

Figure 7

OM images of the PP samples submitted to accelerated degradation with 100× magnification ((A)—sample submitted to a concentration of 2% NaClO for three weeks; (B)—sample submitted to a concentration of 100% NaClO for three weeks; (C)—sample submitted to a concentration of 2% NaClO for three months; (D)—sample submitted to a concentration of 100% NaClO for three months).

Figure 8

SEM images of the PVC sample with 200× magnification after three weeks (A) and three months (B) of immersion. (C) EDS graph of the red zone in (B).

Figure 9

SEM images of the HDPE sample with a 2000× magnification after three weeks (A) and three months (B) of immersion. (C) EDS graph of the red zone in (B).

Figure 10

SEM images of the PP sample with a 200× magnification after three weeks (A) and three months (B) of immersion.

Figure 11

Tensile tests of PVC samples ((A)—control sample; (B)—sample immersed for three weeks in 5% NaClO; (C)—sample immersed for three weeks in 100% NaClO; (D)—sample immersed for three months in 5% NaClO; (E)—sample immersed for three months in 100% NaClO).

Figure 12

Stress–strain curve graphs for the PVC tensile tests for the control sample and the samples immersed in 5% NaClO and 100% NaClO for three weeks (A) and three months (B).

Figure 13

Tensile test HDPE samples ((A)—control sample; (B)—sample immersed for three weeks in 5% NaClO; (C)—sample immersed for three weeks in 100% NaClO; (D)—sample immersed for three months in 5% NaClO; (E)—sample immersed for three months in 100% NaClO).

Figure 14

Stress–strain curve graphs for the HPDE tensile tests for the control sample and the samples immersed in 5% NaClO and 100% NaClO for three weeks (A) and three months (B).

Figure 15

Tensile test of PP samples ((A)—control sample; (B)—sample immersed for three weeks in 5% NaClO; (C)—sample immersed for three weeks in 100% NaClO; (D)—sample immersed for three months in 5% NaClO; (E)—sample immersed for three months in 100% NaClO).

Figure 16

Stress–strain curve graphs for the PP tensile tests for the control and the samples immersed in 5% NaClO and 100% NaClO for three weeks (A) and three months (B).