Water repellency: The water repellent properties of the cotton
fabrics treated with (IB-N-SA) PDMS were evaluated and the grade
of water repellency of treated cotton fabric was 90. Furthermore,
the water contact angle of treated cotton fabric increased from
88.371 to 124.491 as shown in Fig. 1. The reason of the improvement
of water repellency was that (IB-N-SA) PDMS could react
with cotton fiber and the groups which oriented on fiber surface,
mainly methyl groups, formed a hydrophobic film, decreasing the
critical surface tension of cotton fabric [17].
Flame retardant performance: The flammable properties of
cotton fabrics were investigated and the results showed that the
LOI value of treated cotton fabric increased from 18.0% to 30.9%.
The upward burning behaviors of cotton fabrics were also determined
by the vertical burning test and the results demonstrated
that the untreated cotton fabric was completely destroyed while
the treated cotton fabric obtained shorter char length (3.8 cm),
shorter after-glow time (4 s) and no after-flame which indicated
that the flammability of cotton fabric was retarded by (IB-N-SA)
PDMS. The reason was that (IB-N-SA) PDMS decomposed during
degradation and produced the incombustible gases which can
dilute the concentration of the flammable gases and formed the
foamed-char layers. Furthermore, (IB-N-SA)PDMS also produced
silica and glassy char, which acted as a physical barrier and could
protect cotton fabric from heat and oxygen transfer.
Combustion behaviors: Cone calorimeter was employed to investigate
the combustion properties of cotton fabrics, the results are
shown in Fig. 2 and the critical data related to the combustibility are
presented in Table 1. The treated cotton fabric with (IB-N-SA) PDMS
obtained a remarkable reduction in heat release rate (HRR),
corresponding peak HRR (PHRR) and total heat release rate (THR) as shown in Fig. 2(a) and (b), and Table 1. It demonstrates that
(IB-N-SA) PDMS could retard the combustion of cotton fabric
effectively as evident by the extension of time to ignition (TTI,
15 s vs. 2 s) and the increase of FPI value (the ratio between TTI and
PHRR, 0.37 s m2
/kW vs. 0.01 s m2
/kW) as collected in Table 1. The
higher the FPI, the better is the flame retardancy of materials. EHC
(effective heat combustion) and Mass loss are also important
parameters that can reflect the combustibility of cotton fabrics as
shown in Fig. 2(c) and (d). It can be seen that EHC value of the
treated cotton fabric has decreased compared to untreated cotton
fabric (10.17 MJ/kg vs. 12.57 MJ/kg) which means the reduction of
heat released from volatile portion. The Mass loss value of treated
cotton fabric is much lower than untreated one's (5.51 g vs. 12.32 g)
and it indicates the incomplete combustion of cotton fabric. Lower
CO2/CO ratio suggested inefficient combustion of materials [18].
From Table 1, we can know that the CO2/CO ratio of treated cotton
fabric has decreased significantly (7.18 vs. 23.30). All these demonstrate
that the flame retardancy of cotton fabric have been enhanced
due to the employment of (IB-N-SA) PDMS.