Observed results

Biocidal properties of the modified fibers could be demonstrated after a chlorination reaction by exposing the grafted fibers to a diluted chlorine solution, with which the grafted hydantoin rings were converted to N-halamine structures. The polymeric N-halamines could provide powerful and rapid antibacterial activities against E. coli and S. aureus. Most of the fibers could completely inactivate a large number of bacteria (1 x 106 CFU) in a 10-30 min contact time. In addition, the anti-bacterial activities of these polymeric N-halamines could be easily recovered after usage by simply exposing to chlorine solution again.

Figure 6.3 reveals grafting yields on common fabrics using BPO as radical initiator and triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATAT) as a co-monomer in the grafting reactions [12]. These fabrics represent the most commonly employed fabric materials in institutional and consumer uses. The grafting reactions were almost quantitative for several fabrics. However, since BPO is very hydrophobic, it did not work as effectively on cotton fabrics as did hydrophilic radical initiators [12]. Table 6.3 shows the durability of the biocidal functions provided by the ADMH grafted fabrics. The biocidal functions on most hydrophobic fabrics were more durable than those on hydrophilic fabrics and could last for more than 15 washes without recharging. After 50 washes, the lost biocidal functions were fully recharged by a dilute chlorine washing.

The controlled radical grafting reaction also worked effectively on some high performance fabrics such as Nomex, Kermel, and Kevlar/PBI, which are often employed in firefighter and military uniforms. Shown in Figure 6.4 are

Table 6.3. Log reduction of E. coli after washing. (Journal of Applied Polymer Science © 2002)

Log reduction of E. coli (%)

Washing times

Nylon

PET

PP

Acrylic

Cotton

PET/Cotton

0

5

5

5

5

5

5

5

5

5

5

5

3

5

15

5

5

5

5

1

5

30

3

3

2

1

UDa

3

50

UD

1

1

1

UD

UD

50b

5

5

5

5

5

5

Note: contact time = 30 min (E. coli concentration: 105-106 CFU/mL; all of the samples were tested with machine washing following AATCC Test Method 124. AATCC standard reference detergent 124 was used in all of the machine-washing tests. a No reduction of E. coli was detected. b These samples were re-bleached after 50 times of washing.

Note: contact time = 30 min (E. coli concentration: 105-106 CFU/mL; all of the samples were tested with machine washing following AATCC Test Method 124. AATCC standard reference detergent 124 was used in all of the machine-washing tests. a No reduction of E. coli was detected. b These samples were re-bleached after 50 times of washing.

Figure 6.3. Influence of BPO concentration (wt%) on grafting yields [12]. (Journal of Applied Polymer Science © 2002) Grafting conditions: Padding bath contained ADMH, 4 wt%; TATAT, 1.5 wt%; the softener, 1.5 wt%; and different amounts of BPO. The fabrics were dipped and padded twice at a 100% expression, dried at 50 °C for 5 min, cured at 130 °C for 5 min (for PP, the fabric was cured at 105 °C for 5 min), washed, and dried

Figure 6.3. Influence of BPO concentration (wt%) on grafting yields [12]. (Journal of Applied Polymer Science © 2002) Grafting conditions: Padding bath contained ADMH, 4 wt%; TATAT, 1.5 wt%; the softener, 1.5 wt%; and different amounts of BPO. The fabrics were dipped and padded twice at a 100% expression, dried at 50 °C for 5 min, cured at 130 °C for 5 min (for PP, the fabric was cured at 105 °C for 5 min), washed, and dried grafting yields of ADMH on these fabrics. The reaction on Nomex was especially highly efficient with the grafting yields above 4%. This result may be caused by lower crystallinity of the polymer than the other two since the reaction could only occur in amorphous areas of the polymers. Since these fabrics are quite hydrophobic, the adsorption of ADMH on the polymers was relatively difficult, which may contribute to overall lower grafting yields and low biocidal functions on Kermel and Kevlar/PBI fabrics.

Hydrophobic properties may prevent hydrolysis of N -halamine structures on the fabrics. Thus, these fabrics all demonstrated quite durable biocidal to ¿3

BPO Concentration (Wt%)

BPO Concentration (Wt%)

Figure 6.4. Grafting yields on Nomex, Kernel, and Kevlar/PBI fabrics. (Journal of Applied Polymer Science © 2003) Padding bath contained: ADMH, 3 wt%; PEG-DIA, 2 wt%; and the softener, 1.5 wt%. The fabrics were dipped and padded twice at a 100% expression, dried at 50 °C for 5 min, cured at 140 °C for 5 min, washed, and dried.

functions, as shown in Table 6.4. The grafting reactions on Kermel and Kevlar/PBI fabrics were less effective, as observed by the low-active chlorine contents on the fabrics, and low biocidal efficacy.

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