1. Nylon-12 / Sulfur Composite:
Structure, Thermal and Morphological Study
S. Vijay Kumar, Kishore Kumar Jena and Saeed M. Alhassan*
Department of Chemical Engineering, The Petroleum Institute PO Box 2533 Abu Dhabi, United Arab Emirates
MOTIVATION
N-12 E
N-12-S-2.5% N-12-S-5% N-12-S-10% N-12-S-20% N-12-S-30%
Extrudution condition
Temperature C
Cycles min
RPM / min
Sulfur
2.5 %
30 %
5 %
20 %
10 %
More than 70 million tons of elemental sulfur are produced world wide annually of which nearly seven million tons is in excess and majority of which is stored in powder form, or as compressed bricks
Only portion of elemental sulfur is used for the production of sulfuric acid, fertilizers, agrochemicals, cosmetics and in synthetic rubber
The abundance of elemental sulfur offers opportunities to develop new chemistry and processing methods to utilize sulfur as a novel feedstock for synthetic advanced materials.
Efforts to either modify or utilize elemental sulfur to create polymeric materials have been investigated by both polymerization and processing methods.
The preparation of nanocomposite materials with elemental sulfur is a new opportunity in materials chemistry that has not been extensively explored
OBJECTIVE
Figure Digital image of the Nylon-12/sulfur nanocomposites extruded samples with different sulfur loading
Exploration of structural and morphological properties of elemental sulfur as filler in Nylon-12 nanocomposites
RESULTS AND DISCUSSION
The distinct peak of more stable γ-phase of Nylon-12 appears at 2θ = 21.42° (d = nm). Incorporation of sulfur as filler disturb the crystalline region and increase the amorphous phase of Nylon-12. Sulfur completely diffused in to the Nylon-12 matrix in the melt state under the extrudution condition. During extrudution, the fast solidification of sulfur in the Nylon-12 matrix may inhibit the crystalline process of the polymer lamellae and hence hinders the growth of crystalline phase in the Nylon-12. Thus, with the increasing amount of sulfur total crystallinity of the Nylon-12 decreases.
The spectra of Nylon-12/sulfur composites are identical to that of Nylon. Since sulfur is IR inactive and no new peaks are appeared in the composite suggests that, the sulfur and Nylon did not undergo any chemical reaction.
Figure FTIR spectra of Nylon-12 and
Nylon-12/sulfur composites
Figure XRD of Nylon-12/sulfur composite with different sulfur loading
The peaks corresponds to the melting and crystallization of sulfur were not observed in Nylon-12 nanocomposites, which led us to conclude that sulfur is predominantly converted to its amorphous form and uniformly dispersed in Nylon-12 matrix. The percentage crystallinity in pure Nylon-12 is calculated to be 22.8%. The degree of crystallinity for the nanocomposites decreases with the increasing sulfur loading and the reaches the lowest crystallinity of 15.9 % for the highest sulfur loading of 30 wt %. However, the crystallization temperature (Tc) is largely remains unchanged with different sulfur loading.
The percentage crystallinity (Xc) can be calculated by
Xc =∆H/∆H0F
Table Melting temperature (Tm), crystallization temperature (Tc), enthalpy of melting (∆Hm), enthalpy of crystallization (∆Hc) and degree of crystallinity (χc)
Sl no
Sample Name
Tm in C
Tc in C
∆Hm J/g
∆Hc J/g
Xc in % 1
Pure Sulfur
106, 124 & 184
35.6
6.5, 37.7 & 4.5
-28.14 2
N-12
182
152.6
37.58
-47.73
22.81 3
N12_S-2.5%
181.5
149.0
35.39
-46.06
22.01 4
N12_S-5%
180
146.8
33.66
-45.59
21.79 5
N12_S-10%
174.8
152
32.23
-43.82
20.94 6
N12_S-20%
175.5
151.2
28.44
-37.08
17.72 7
N12_S-30%
173
152.1
23.78
-33.43
15.97
Figure DSC Thermogram of Nylon-12, sulfur and Nylon-12/Sulfur composites
Magnification 300X
N-12_S-2.5%
N-12_S-20% C S
CONCLUSIONS
Figure SEM mapping images of Nylon-12 and sulfur composite (Red -carbon and Green- sulfur)
This work shows for the first time; the use of elemental sulfur in composite formulations with no cross-reaction with host matrix. Composites were prepared using extrusion at temperature above sulfur polymerization temperature. Processing of sulfur and nylon proceeded without complication and without the need for modifications of either constituent. Sulfur loading up to 30 wt% was achieved. The sulfur loading decreases the overall crystallinity of the host polymer and also effects on the melt and crystallization temperature. The present study opens the door for further research on sulfur as filler in composite materials.
Figure shows the smooth surface of extruded samples. This indicates the uniform distribution of sulfur in the Nylon-12 matrix without any macro phase separation or aggregation of sulfur even at 30 wt% loading. Carbon-Sulfur mapping of composite with 2.5 and 20 wt% sulfur loading is also supports the uniform distribution and the formation of single phase composite
ACKNOWLEDGEMENTS
This work is funded by the Gas Subcommittee of Abu Dhabi National Oil Company (ADNOC) Research & Development.