Gypsum polymer composites 2008

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A Study on Constitution and Properties of Gypsum-Polymer Composites

Author: Hesham Abdel Rehim, MSc. Supervisor: Assoc. Prof., RNDr. Ondrej Gedeon, Ph.D.

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Gypsum is considered as one of the most common non-metallic minerals.

It consists of calcium sulphate dihydrate (CaSO4.2H2O).

It occurs in various forms such as Selenite, Alabaster, Satin spar, Rock gypsum and Gypsite.

It is the mother rock for different chemical industries and various applications.

When pure it contains 32.5 wt. % Lime (CaO), 46.6 wt. % sulphur trioxide (SO3) and 20.9 wt. % water.

It is one of the softest mineral, with a hardness of 2.0 on the Mohs’ scale of hardness (Phillips and Griffin1981).

Introduction

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Dehydration:

CaSO4.2H2O + Energy → CaSO4.½H2O + 1½ H2O

CaSO4.½H2O + Energy → -CaSO4 + ½H2O

Gypsum Technology

Rehydration:

CaSO4.½ H2O+ 1½H2O → CaSO4.2H2O + Energy

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1. Wall Lining

2. Roof Lining

3. Floors

4. Partitions

5. Ceilings

Living with gypsum ...

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The study aimed at the investigation of the effect of using three different vinyl-based polymers on

• The mechanical properties of the formed composites. • The microstructure of the formed composites. • Preliminary bioactivity of the formed composites.

Aim of the work

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Vinyl-based polymers

[ CH2CH ]n

OH

CH2COOH

[ CH2CH ]x [ CH2CH ]y [ CH2C ]z

OH COOCH3 COOH

[ CH2CH ]x [ CH2CH ]y [ CH2CH ]z

Cl COOCH3 OH

PVA

P(VA-co-VAc-co-It)

P(VC-co-VAc-co-VA)

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1. Assessment of the starting materials (Plaster & polymers).

2. Formation of different polymer/plaster composites.

3. Measuring of the mechanical properties.

4. Correlation with the microstructure.

5. Studying of the bioactivity of gypsum and gypsum- polymer composites.

Experimental WorkExperimental Work

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Type SiO2 R2O3 CaO MgO SO3 *H2O *CO2 NaCl

Wt. % 0.44 0.02 38.53 0.64 53.55 5.28 1.54 Trace

Mol % 0.43 8.96 x103 40.41 0.93 39.18 16.99 2.05 Trace

Normal Consistency

(%)

Setting Time (min)

Mechanical Properties

CompressiveStrength (MPa) Bending Strength (MPa)

46Initial Final one day 3 days 7 days one day 3 days 7 days

26’30” 30’00” 8.5±09 17.7±3 18.2±2 4.3±02 6.7±02 8.7±02

•H2O and CO2 were determined by weight loss at 240 and 1000 oC respectively.

XRF data of the tested plaster

Physicomechanical properties of the tested plaster

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Polymer/plaster wt. %

Compressive Strength (MPa) Bending Strength (MPa)

One Day 3 Days 7 Days One Day 3 Days 7 Days

0.00 8.5 ± 0.2 17.7 ± 0.2 18.2 ± 0.2 2.3 ± 0.2 6.7 ± 0.2 8.7 ± 0.2

0.25 10.8 ± 0.6 18.7 ± 0.8 22.2 ± 0.7 --- --- ---

0.5 10.9 ± 0.5 23.2 ± 1.0 25.0 ± 0.3 4.5 ± 0.1 10.8 ± 0.2 11.3 ± 0.2

1.0 12.9 ± 0.4 28.4 ± 0.4 28.5 ± 0.1 4.9 ± 0.1 13.1 ± 0.2 14.5 ± 0.2

2.0 9.2 ± 0.6 19.6 ± 1.2 22.8 ± 0.7 4.1 ± 0.1 10.4 ± 0.2 11.9 ± 0.4

3.0 8.6 ± 0.6 17.5 ± 0.4 22.0 ± 0.6 --- --- ---

4.0 7.6 ± 0.3 16.1 ± 0.3 19.5 ± 0.7 --- --- ---

PVA/plaster composites

Mechanical properties

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1 2 3 4 5 6 76

8

10

12

14

16

18

20

22

24

26

28

30

Com

pres

sive

str

engt

h (M

Pa)

Aging time (day)

0.0 wt.% 0.25wt.% 0.50wt.% 1.0 wt.% 2.0 wt.% 3.0 wt.% 4.0 wt.%


0 1 2 3 45

10

15

20

25

30

Co

mp

ress

ive

stre

ng

th (

MP

a)

Polymer concentration (Wt. %)

One day 3 days 7 days

1- Compressive strength with aging time

2- Compressive strength with polymer concentration

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Microstructure

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P(VA-co-VAc-co-It)/plaster composites

Polymer wt. %



0.0 8.5 ± 0.21 17.7 ± 0.18 18.2 ± 0.16 2.3 ± 0.16 6.7 ± 0.19 8.7 ± 0.23

0.2 8.8 ± 0.05 19.2 ± 0.14 19.7 ± 0.10 --- --- ---

0.4 9.2 ± 0.11 19.9 ± 0.15

20.8 ± 0.08 --- --- ---

0.6 9.5 ± 0.16 20.2 ± 0.05 21.5 ± 0.09 --- --- ---

0.8 9.9 ± 0.07 20.7 ± 0.11 21.7 ± 0.05 --- --- ---

1.0 10.1 ± 0.06 21.6 ± 0.09

22.3 ± 0.11 2.4 ± 0.05 6.4 ± 0.08 8.6 ± 0.11

1.2 10.4 ± 0.07 23.1 ± 0.00

23.2 ± 0.25 3.1 ± 0.09 7.1 ± 0.05 9.2 ± 0.08

1.4 9.3 ± 0.06 20.4 ± 0.13

21.4 ± 0.11 2.9 ± 0.09 6.7 ± 0.06 8.7 ± 0.11

1.6 9.1 ± 0.05 19.9 ± 0.08 20.9 ± 0.06 --- --- ---

2.0 8.0 ± 0.05 17.9 ± 0.07 19.1 ± 0.11 --- --- ---


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1 2 3 4 5 6 7 86

8

10

12

14

16

18

20

22

24

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0.0wt.% 0.2wt.% 0.4wt.% 0.6wt.% 0.8wt.% 1.0wt.% 1.2wt.% 1.4wt.% 1.6wt.% 2.0wt.%

Co

mp

ress

ive

stre

ng

th (

MP

a)

Aging time (day)




0.0 0.4 0.8 1.2 1.6 2.0 2.46

8

10

12

14

16

18

20

22

24

Co

mp

ress

ive

stre

ng

th (

MP

a)

Polymer concentration (Wt.%)


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Microstructure

Neat plaster

2.0 wt. %

1.2 wt. %

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Polymer wt. %



0.0 8.5 ± 0.21 17.7 ± 0.18 18.2 ± 0.16 2.3 ± 0.16 6.7 ± 0.19 8.7 ± 0.23

1.0 11.0 ± 0.12 18.0 ± 0.05 18.9 ± 0.08 --- --- ---

2.0 12.1 ± 0.06 18.8 ± 0.07 19.3 ± 0.05 --- --- ---

3.0 12.6 ± 0.09 19.2 ± 0.08 20.1 ± 0.06 2.6 ± 0.05 7.8 ± 0.11 8.1 ± 0.07

4.0 13.2 ± 0.05 19.9 ± 0.08 21.0 ± 0.16 2.9 ± 0.09 8.0 ± 0.19 8.9 ± 0.13

6.0 9.9 ± 0.08 17.8 ± 0.13 17.9 ± 0.05 2.9 ± 0.05 6.4 ± 0.12 6.8 ± 0.07

8.0 8.3 ± 0.06 17.3 ± 0.12 17.7 ± 0.09 --- --- ---

P(VC-co-VAc-co-VA)/plaster composites


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1 2 3 4 5 6 7

8

10

12

14

16

18

20

22

Co

mp

ress

ive

stre

ng

th (

MP

a)

Aging time (day)

0.0 wt.% 1.0 wt.% 2.0 wt.% 3.0 wt.% 4.0 wt.% 6.0 wt.% 8.0 wt.%



0 2 4 6 8

9

12

15

18

21

Com

pres

sive

str

engt

h (M

Pa)

Polymer concentration (Wt.%)



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Microstructure


1 wt. % 2 wt. % 3 wt. %

8 wt. %4 wt. % 6 wt. %

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Microstructure


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X- Ray diffraction


1 wt. % 8 wt. %

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Neat plaster

PVA/plaster1.0 wt. %

P(VA-co-VAc-co-It)/plaster1.2 wt. %

P(VC-co-VAc-co-VA)/plaster4.0 wt. %

28.5 MPa(56 %)

23.2 MPa(27 %)

21.0 MPa(15 %)

18.2 MPa

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0 2 4 6 8 10 12 140

100

200

300

400

500

600

700

800

900

1000

Con

cent

ratio

n (m

g/L)

P

Ca

C

once

ntra

tion

(mg/

L)

Soaking time (days)

Neat Gypsum Gypsum/PI Gypsum/PII Gypsum/PIII

0

10

20

30

40

50

60

70

80

90

100

Bioactivity of Gypsum and Gypsum-Polymer Composites

Ca and P concentrations

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0 2 4 6 8 10 12 147.50

7.55

7.60

7.65

7.70

7.75

7.80

7.85

7.90pH

Soaking time (days)

Neat Gypsum Gypsum/PI Gypsum/PII Gypsum/PIII


Variations in the pH of SBF solutions

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Neat plaster Gypsum after treatment in SBF followed by 1.5 SBF for a week (Low

Magnification)

Gypsum after treatment in SBF followed by 1.5 SBF for a week

(High Magnification)

Energy-dispersive x-ray analysis of the spot marked by

X in micrograph (c).

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Phase compositions of gypsum and gypsum-polymer composite solids after immersion in SBF and 1.5 SBF solutions for a week in each.

20 22 24 26 28 30 32 34 36 38 40

GGGGG

G

GG

G

GG

G

G G: GypsumHAp: Hydroxyapatite

HApPolymer III

Polymer II

Polymer I

Arb

itra

ry U

nit

s

2 (degrees)

No Polymer


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Scanning electron micrographs of gypsum composites containing a) polymer I, b) polymer II and c) polymer III after immersion in SBF for one week.


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Scanning electron micrographs of gypsum composites containing a) polymer I, b) polymer II and c) polymer III after immersion in SBF for one week, followed by 1.5 SBF for one week.


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SEM micrographs of a) Apatite spherolites grown on a gypsum/polymer II composite, and b) Detailedultrastructure of a spherolite grown on gypsum/polymer III composite.


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The purity of the tested gypsum plaster sample was calculated to be around 96 % CaSO4.½H2O with small amount of siliceous materials and carbonates. The carbonates were calculated to be 1.34 % of MgCO3 and 1.9 % of CaCO3.

The investigated gypsum plaster sample blended 46 % water and gave long setting time (30 min) with moderate mechanical properties, 8.7 and 18.2 MPa for bending and compressive strengths respectively.

PVA/plaster composites showed a 56% increase in the compressive strength achieving 28.5 MPa with the addition of only 1.0 % by weight of PVA.

The influence of addition of P(VA-co-VAc-co-It) to plaster at a slightly higher concentration; 1.2 wt. % showed a maximum compressive strength of 23.2 MPa, which is 27% higher than that of polymer-free gypsum.

Conclusions

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P(VC-co-VAc-co-VA)/plaster composites achieved a compressive strength value of 21.0 MPa, which is 15% higher than that of polymer-free gypsum (when the polymer added in 4.0 wt. %).

Findings showed a correlation between the polymer solubility as well as its chemical structure with its effect on the mechanical properties of the produced composites.

Selected gypsum-polymer composites with the highest mechanical properties were further evaluated for their preliminary bioactivity. SEM micrographs of the SBF-treated composites revealed the formation of bone-like apatite deposits on the composite surfaces as well as inside the open pores. Water insoluble copolymer P(VC-co-VAc-co-VA) showed the greatest extent of apatite coating.

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- Onderj Gedeon Doc.RNDr., Ph.D.- Aleš Helebrant Doc. Ing., CSc.- Jana Andertová Ing., CSc.- Jan Macháček Ing., Ph.D.- Dana Rohanová Dr. Ing.

Acknowledgement

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Thank you for your attention