Mechanical characteristics of low-density polyethylene and materials, perspective for applying in impervious structures | Статья в журнале «Молодой ученый»

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Рубрика: Технические науки

Опубликовано в Молодой учёный №2 (136) январь 2017 г.

Дата публикации: 13.01.2017

Статья просмотрена: 12 раз

Библиографическое описание:

Огородов Л. И., Лустина О. В. Mechanical characteristics of low-density polyethylene and materials, perspective for applying in impervious structures // Молодой ученый. — 2017. — №2. — С. 181-185. — URL https://moluch.ru/archive/136/38038/ (дата обращения: 11.12.2018).



Structure protection against groundwater and surface water (spring waters, precipitation and flood) is a topical branch in hydrotechnical, road, industrial and civil engineering. In the process of sumps, waste collectors, heaps and pool converters operation there is a danger of a leakage of ecologically unsafe substances, which differ from each other in composition and the degree of aggressiveness. Natural and artificial ponds rise the groundwater on adjoining territories, which prevents the economic activity of people. Impervious structures are used for ground and soil structures protection [1, 2]. Different ways of installation of impervious structure elements in soil, foundations, slopes, weirs and dams are known. Laying of the polymer panels on the slopes of the soil structures under the layer of the bulk material, trench and trenchless (vibratory) screen drives are applied. Polymer impervious screens, curtains and membranes are widely spread. Most of the film members were made and are made of low-density polyethylene (LDPE), but other polymer and composite polymer materials are becoming more and more popular [3–5].

Almost all materials have properties changing in time (ageing), especially characteristic it is for polymer and composite polymer materials [6–9], as well as steels and alloys [10]. The speed of ageing depends on sensitivity of a material to acting factors and their intensity. The properties changes can be reversible and irreversible. Reversible changes disappear almost entirely after external factors eliminated. The opposite situation takes place in irreversible changes. As we aim to predict the durability of ready-made materials, so we can define ageing as appearance of transformation during storage and exploitation.

The objectives of the present paper are:

  1. To estimate the impact of the long-term ageing under load on the mechanical characteristics of the LDPE samples.
  2. To compare the results of the experiment with LDPE samples stabilized with 2 % soot content under long-term ageing conditions and under influence of CHP ash.
  1. The estimation of the influence of the long-term ageing on mechanical characteristics of low-density polyethylene during storage and under load
    1. The samples and equipment

LDPE samples were made in laboratory complex in All-Union Scientific Research Institute of Hydraulic Engineering named after B. E. Vedeneev. The samples had a shape of a shoulder blade with 25 mm working part length and 3,5 mm width. The thickness was ranged from 0,048…,0,064 mm to 0,16…0,23 mm.

Samples of stabilized LDPE had a shape of a shoulder blade with 30 mm working part length, 3,5 mm width and thickness mm.

LDPE and stabilized LDPE samples were cut in the direction and cross-direction of the film extrusion.

Uniaxial sample tension tests were carried out using FPZ-100/1 and RMI-5 (РМИ-5) installations with different capture displacement speeds (v, mm/min.). Depending on the thickness, the samples were grouped in three, which then were tested and results of the experiment were presented as the mean values. The experiments with long-term loaded samples were held on one specimen. The dimensions of these samples were determined before tension test.

1.2. The results of tests

Mechanical characteristics (σρr– proportional limit, и — limit stress and deformation, — elastic modulus) of low-density polyethylene (LDPE) under tension (v = 50 mm/min., ) are shown in Table 1.

Table 1

Mechanical characteristics of LDPE in original state (the mean values of 3 samples)

Group of samples

In the direction of the film extrusion

In the cross-direction of the film extrusion

σpr, mPa

σρ, mPa

ερ, %

Ερ, mPa

σρr, mPa

σρ, mPa

ερ, %

Ερ, mPa

1

8,70

15,30

450

73,2

8,44

13,64

470

149,8

2

8,98

16,87

460

154,0

8,39

16,48

540

79,8

3

9,02

16,78

472

110,8

8,73

15,89

512

89,2

4

8,29

15,79

445

105,9

8,36

15,40

558

92,6

5

8,81

16,87

450

109,4

8,68

9,37

295

84,8

Mean

8,76

16,32

455

110,7

8,52

14,16

475

92,2

LDPE samples (in the direction of the film extrusion) have more stable mechanical properties and higher density than samples, made crosswise of the film extrusion.

Limit stress and the value of the elastic modulus are higher in samples cut in the direction of the film extrusion, than in samples cut in the cross-direction of the film extrusion. The influence of the sample thickness in specified range on LDPE mechanical characteristics (Table 1) is insignificant. The results of tension tests (V = 50 mm/min.) of LDPE samples (along of the extrusion) with thicknesses δ = 0,048…0,064 mm confirm this conclusion.

Table 2

Mechanical characteristics (in the direction of the extrusion) of LDPE samples

Sample

δ, mm

σρr,mPa

σρ, mPa

ερ, %

1

0,052

7,19

14,32

275

2

0,051

8,13

13,93

240

3

0,054

8,59

16,97

360

4

0,064

7,55

16,09

395

5

0,048

8,47

15,40

295

Mean

0,054

7,98

15,34

317

LDPE samples (δ = 0,16…0,23 mm) were loaded by constant tensile load during 189–194 months (~16 years). In the first series of experiments (189 months), initial stresses of ageing under load σН were recorded. In the second series of experiments (194 months), beside σН, the relative deformation of LDPE samples was recorded in the beginning (εН) and in the end (εк) of ageing. Tables 3–5 show the results of experiments (σut — the durability limit under tension, εnt — deformations corresponding to the durability limit). Table 6 shows the data of the comparison of obtained results.

Table 3

Mechanical characteristics of LDPE (in the direction of the extrusion) after long-term (189 months) uniaxial compressive loading

Sample

σН, mPa

σρr, mPa

σρ, mPa

ερ, %

Ερ, mPa

1

0,87

2,93

10,55

336

132

2

1,31

5,77

16,16

503

138

3

1,76

5,77

14,01

470

137

4

2,18

5,84

12,59

298

142

5

2,63

5,49

13,86

483

133

Mean

-

5,17

13,43

418

136

Table 4

Mechanical characteristics of LDPE (in the direction of the extrusion) after long-term (194 months) uniaxial tensile loading

Sample

σН, mPa

εн, %

εк, %

σρr, mPa

σρ, mPa

ερ, %

Ερ, mPa

σut, mPa

εut,%

1

2,63

5,3

6,3

5,50

13,86

480

135

13,86

+

2

5,36

20,8

26,9

5,52

13,63

146

125

13,46

47,0

3

6,25

38,5

59,2

4,71

14,69

78

126

15,25

46,2

4

7,15

51,7

71,2

4,96

17,08

140

122

17,48

41,9

5

8,03

94,5

118,9

5,60

25,21

131

123

25,21

41,8

Mean

-

-

-

5,26

16,89

195

126

17,05

44,2

Table 5

Mechanical characteristics of LDPE (in the cross-direction of the extrusion) after long-term (194 months) uniaxial tensile loading

Sample

σН, mPa

εк, %

σρr, mPa

σρ, mPa

ερ, %

Ερ, mPa

σut, mPa

εut,%

1

0,85

2,4

4,96

12,80

707

85

8,41

27,3

2

2,56

5,6

4,54

12,20

572

80

8,65

-

3

4,26

10,0

4,56

10,88

480

72

-

-

4

5,11

24,4

3,75

14,69

540

58

10,31

57,8

5

5,95

21,2

4,04

17,69

487

95

12,69

42,5

6

5,95

30,4

3,96

12,07

224

65

12,24

52,1

Mean

-

-

4,30

13,39

502

81

10,46

44,9

Table 6

Mean values of LDPE mechanical characteristics in original state and after long-term ageing under the load

The sample direction

The sample state

σρr, mPa

σρ, mPa

ερ, %

Ερ, mPa

Direction of the extrusion

Original

8,76

16,32

455

111

Original (thin samples)

7,98

15,34

317

-

After loading 189 months

5,17

13,43

418

136

After loading 194 months

5,29

16,89

195

126

After loading σН< 3 mPa

5,22

13,50

428

136

After loading σН> 3 mPa

5,20

17,65

124

124

Cross-direction of the extrusion

Original

8,52

14,16

475

92

After loading 194 months

4,30

13,39

502

81

After loading σН< 3 mPa

4,75

12,50

640

82

After loading σН> 3 mPa

4,08

13,83

433

80

Let us consider the results of the LDPE stabilized by 2 % content of soot tests. Samples of the first series were kept in conditions of heated (without sunlight access) warehouse space during 17 years, and the samples of the second series — in the ash of Magadan CHP during the same time. The samples are oriented in the cross-direction of the extrusion. In each series of the tests, 3 samples were used. Table 7 shows results of the uniaxial tension tests and Table 8 shows their comparisons.

Table 7

Mechanical characteristics of stabilized LDPE samples

Series

V, mm/min.

I series

II series

σρr, mPa

σnt, mPa

εnt,%

Ερ, mPa

σρr, mPa

σut, mPa

εut,%

Ερ, mPa

1

0,4

2,5

8,7

20,3

140

6,4

9,5

20,0

100

2

2,0

3,0

10,0

20,3

180

7,0

10,7

20,8

120

3

20,0

3,5

11,4

18,0

200

7,7

12,1

19,2

135

4

100,0

4,0

12,4

18,0

240

8,5

13,2

12,5

185

Table 8

Comparison (in%) between the values of the LDPE mechanical characteristics of the second series and the first one

Mechanical characteristics

The deformation speed V (mm/min.)

0,4

2,0

20,0

100,0

σρr

+156,0

+133,0

+120,0

+112,0

σnt

-9,2

+7,0

+6,1

+6,4

εnt

+1,5

+2,5

+6,7

-30,6

Ερ

-28,6

-33,3

-32,5

-22,9

Table 9 shows the results of uniaxial tension tests of LDPE samples (stabilized with 2 % soot content) in original state (I) and after ageing (II) during 18 years. The deformation speed was 50 mm/min.

Table 9

Mechanical characteristics of stabilized LDPE in original state and after 18 years of ageing in natural storage conditions

The direction of the sample cutting

σρ, mPa

Change,

%

ερ, %

Change,

%

I

II

I

II

In the direction of the extrusion

14,9

16,8

+ 12,8

476

633

+ 33

In the cross-direction of the extrusion

12,9

11,8

- 8,5

552

575

+ 4,2

Conclusions

The film of the examined polyethylene of low density (LDPE) in original state has stable mechanical characteristics with some anisotropy related to the direction of the extrusion.

The LDPE long-term ageing (16–17 years) under load in heated warehouse space conditions decreases the proportional limit on 45 % (average), besides the values of the elastic modulus increases on 22 % in the direction of the film extrusion and decreases on 12 % in the cross-direction of the extrusion. The LDPE ageing under load with tensile stresses less than 3 mPa decreases limit stresses under short-term uniaxial tension up to 17 %. The LDPE ageing under load with tensile stresses higher than 3 mPa increases limit stresses under short-term uniaxial tension (in the direction of the extrusion) on 8 % with the deformation decrease more than triple. For samples cut in the cross-direction of the film extrusion the changes are insignificant.

The mechanical characteristics of unstabilized and stabilized by 2 % soot content LDPE are insignificantly different. Natural ageing during 18 years in heated warehouse space conditions of stabilized LDPE does not lead to significant changes of limit stresses and deformations under uniaxial tension.

The influence of the Magadan CHP ash during 17 years does not change significantly the stabilized LDPE mechanical characteristics. The change of the elastic modulus (the average decrease on 29 %) has to be considered in calculations of film impervious structure elements.

References:

  1. The researching problems in the field of creating non-subterranean impervious structures of retaining structures / A. L. Goldin, V. P. Lysenko, G. V. Borisov, V. G. Radchenko // The materials from hydrotechnical conferences: Non-subterranean impervious structures and waterproof of energy structures / B. E. Vedeneev VNIIG. 1990.P. 6–13.
  2. Glebov V. D. Polymer film impervious structures of hydrotechnical subterranean structures. Synopsis thesis, doctor. L.: 1982. 52 p.”
  3. Ogorodov L. I., Pavlov P. A., Glebov V. D. The resistance of long-term high-density polyethylene destruction. The application to the estimation of the waterproof resource / The problems of modifying asphalt polymer structures of hydrotechnical structures: The materials from hydrotechnical conferences. L.: Energoatomizdat, 1986. P. 110–113.
  4. Khrulev V.M Perspective waterproofing and soil stabilizing polymer materials // University news. 1998. № 4–5. P. 139–140.
  5. Ogorodov L. I. The estimation of the operability of materials used in road and hydrotechnical construction // Topical issues of modern road construction and economy: The materials of the All-Rusian scientific-practical conference. Vologda: VoGTU, 2002. P. 109–111.
  6. Pavlov N. N. Plastic ageing under natural and artificial conditions. M.: Chemistry, 1982. 224p.
  7. Kirillova E. I., Shulgina E. S. Ageing and stabilization of thermoplastics. L.: Chemistry, 1988. 240 p.
  8. Pavlov P. A., Ogorodov L. I. Long-term resistance of polymer and composite materials considering the long-term ageing // Mechanics of composite materials. 1991. № 4. P. 692–696.
  9. Lysenko V. P., Ogorodov L. I., Pavlov P. A. Accounting of long-term natural ageing of polymer materials and estimation of long-term resistance of hydrotechnical structure film elements // Non-subterranean impervious structures and waterproof of energy structures. L.: Energoatomizdat. 1990. P. 140–147.
  10. Yamaleyev K. M., Abramenko L. A. Deformational ageing of tube steels during operation of the main oil pipelines // The durability issues. 1989. № 11. P. 125–128.
Основные термины (генерируются автоматически): LDPE, CHP, VNIIG.


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