1. Novel semihydrophilic modified montmorillonites
for polymeric composites
Magdalena Zdanowicz, Tadeusz Spychaj, Krzysztof Kowalczyk West Pomeranian University of Technology in Szczecin, Polymer Institute ul. Pulaskiego 10, Szczecin,
INTRODUCTION
RESULTS
Layered aluminosilicates are known as nanofillers for polymeric materials (cast compositions, films, adhesives and coatings), allowing to enrich e. g. their good mechanical and barrier properties. High compatibility and dispersion in the polymer matrix are key factors affecting improvement of the composites final properties. Due to hydrophilic character of pristine aluminosilicates they are organo-philized before an introduction into polymer matrix.
Commercial montmorillonites treated with organic ammonium salts are commonly intended for hydrophobic systems and exhibit low affinity and degree of dispersion in semihydrophilic and hydrophilic polymers e.g. polyurethanes (or polyols for synthesis), thermoplastic starch, poly(vinyl alcohol) [1,5].
This work presents results of sodium montmorillonite (Bentonit Specjal, ZGM Zebiec) modification with prepared novel semi-hydrophilic salts of different molecular weight, including two ammonium cations and few hydroxyl groups (Fig. 1).
Table 1. Characteristics of unmodified sodium montmorillonite (MMT-Na) and MMT-Na modified with semihydrophilic diammonium salts
Sample
Molecular weight [g/mol] M*
[g/mol]
d-spacing
[nm]
Bulk density
[g/cm3]
Content of
organic salt
[%]
Filtration
MMT-Na —
1.14
0.60
TEE
1176.4
262
4.91
0.47
41.8
TEH
1144.7
230
4.29
0.36
21.9
TGE6
1555.5
641
3.97
0.42
25.1
TGE8
1765.4
851
4.16
0.39
27.5
*Approximated value of molecular weight of chain between ammonium cations
Figure 2. XRD patterns for pristine purified MMT-Na, montmorillonite ogranophilized with TEE and TEH diammonium salts (A) and montmorillonite organophilized with TGE6 and TGE8 (B)
d-spacing
Figure 1. Scheme of the MMT-Na organofilization through cation exchange
Figure 3. The dependence viscosity/
rotational speed of suspensions:
A – MMT-Na/glycerol
B – Cloisite 30B/ glycerol
C – TEE/glycerol
Water slurries of sodium montmorillonite (MMT-Na) have been purified using centrifuge separator. Organophilization was performed for 2 h at 60°C. Washed, dried, powdered and sieved semihydrophilic organomontmorillonites (OMMT) were analyzed using XRD for measurement of interlayer spacing (X’pert Pro, PANalytical). Description of ammonium modifiers and OMMT obtained are given in Table 1 and Figure 2.
Suspensions of MMT-Na, prepared OMMT’s, as well as, suspensions of commercial organomontmorillonite Cloisite 30B in glycerol have been prepared and their rheological features evaluated comparatively (using Brookfield D-VIII viscometer with plate-cone measurement system). Viscosity measurements of clay/glycerol systems were carried out at 25±1°C with increasing (from 1 to 50 rpm) and decreasing (from 50 to 1 rpm) rotational speed (Fig. 3). Concentration of MMT-Na or OMMT in suspensions were 12 wt. %.
EXPERIMENTAL
CONCLUSIONS
MMT modified with analysed diammonium salts reached large interlayer distances (up to 4.91 nm) in comparison with either pristine sodium montmorillonite (1.14 nm) or semihydrophilic commercial OMMT organophilized with monoammonium salt.
Ability for filtration - parameter important from technological viewpoint - seems to be satisfied for some of OMMT raw products.
Rheological features for the compared montmorillonite/dispersions of OMMT-TEE differ from these of MMT-Na and Cloisite 30B.
References
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