1 Introduction
2 Materials and methods
2.1 Surface morphology
2.2 Water absorption test
2.3 Dynamic vapour sorption
2.4 Calculation of moisture content
2.5 Porosity
2.6 Fourier transform infrared spectroscopy
2.7 Thermal analysis
3 Results and discussion
3.1 Characterisation of the surface morphology
3.2 Characterisation of surface chemistry
Wavenumber (cm−1) | Vibration | Source |
---|---|---|
3341 | O–H stretch | Polysaccharides |
2918 | C–H vibration | Polysaccharides |
2851 | CH2 stretch | Wax |
1742–1733 | C=O stretch in unconjugated ketone, carbonyl and ester groups | Hemicellulose, wax |
1605–1639 | C=C stretch | Lignin |
1630–1660 | −OH | Adsorbed water |
1424 | CH2 bending, C=C stretching in aromatic group, CH in plane deformation | Cellulose, lignin |
1373 | CH bending | Cellulose |
1319 | C–C stretch, CH2 vibration | Lignin, cellulose |
1027 | C–C, C–OH, C–H ring and side group vibration | Hemicellulose, pectin |
1000–1100 | Si–O–Si | Silica |
940–960 | Si–OH | Silica |
896 | C–O–C glycosidic stretch, O–H bending | Polysaccharides |
780–800 | Si–O–Si, SiOCH2CH3—incomplete hydrolysis of TEOS | Silica |
3.3 Water absorption
Coating layers | Eq. (5) parameters | |||
---|---|---|---|---|
a
|
b
|
c
|
R
2
| |
Uncoated | 1198.0 | 0.97 × 10−7 | 0.1327 | 0.9504 |
1 | 182.2 | 0.0033 | 0.334 | 0.9814 |
2 | 173.9 | 0.0006 | 0.2446 | 0.9975 |
5 | 93.89 | 0.0019 | 0.307 | 0.9821 |
8 | 72.81 | 0.0027 | 0.2978 | 0.9948 |
10 | 53.41 | 0.0066 | 0.2611 | 0.9365 |
3.4 Dynamic vapour sorption
3.5 Porosity
3.6 Thermal analysis
Samples | T5 (°C) | T50 (°C) | Tmax (°C) | Residue |
---|---|---|---|---|
Uncoated shiv | 50 | 325 | 329 | 17.5% |
Shiv—1 coat | 185 | 415 | 325 | 41.9% |
Shiv—10 coats | 180 | – | 334 | 63.5% |
Silica | 96 | – | 170 | 69.7% |