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A Chitosan-based flocculant prepared with gamma-irradiation-induced…
A Chitosan-based flocculant prepared with gamma-irradiation-induced grafting
Results and discussion
3.1: Effect of acetic acid concentration and selection of extraction solution
Removal of homopolymer (PAM) with Soxhlet extraction method and their influences
ethanol - PAM cannot be dissolved
acetic acid-glycol - PAM was gelatiniform and difficult to dried
ethanol-water - PAM can be removed effectively, loose and easy to dried.
Invariable result was obtained because acetic acid concentration had no significant effect on the grafting percentage.
To evaluate the effects of acetic acid concentration on grafting percentage
3.2: Characterization of the graft copolymer
3.2.1: FTIR spectrum
at the band 1597/cm- characteristic peak of primary amine N-H vibration in chitosan disappeared in the spectra because it has been deformed. Grafting occurred at amide group.
at the peaks 1667/cm and 1616/cm- absorption of amide I and amide II of polyacrylamide occurred. Proves that it was successfully grafted onto chitosan backbone.
To confirm the occurrence of graft copolymerization
3.2.2 XRD Patterns
• The XRD pattern of chitosan showed two reflections falling at 2h = 10.4 and 20.1, respectively.
• The reflection at 2h = 10.4 was attributed to the hydrated crystals of low crystallinity and corresponded to the form I (Milot et al.,1998), while the reflection at 2h = 20.1 was identified as representative of the crystallinity of the form II (Wu et al., 2005). For the grafted polymer.
• The peak at 2h = 10.4 disappeared, whereas the peak at 2h = 20.1 decreased drastically, which could be attributed to the decrease in crystallinity.
• This suggests that the hydrogen bonding ability of chitosan was reduced after the grafting
of acrylamide onto chitosan backbone.
3.2.3 TGA
• Chitosan occurred lost in weight during stage 1 and 2.
At the first stage, weight loss is cause by loss of adsorbed and bound water.
• The thermal behavior of the chitosan-g-PAM was different from that of chitosan.
While for the second stage is cause by the decomposition of chitosan.
The differential TGA curve, abbreviated as DTG curve, suggests that the temperatures for the rapid weight loss at the two stages were 78 and 313 C, respectively.
3.3: Factors influencing grafting percentage
3.3.1. Total radiation dose
An experiment with 4 different dose rates were conducted
14.3 Gy/min
18.1 Gy/min
11.7 Gy/min
25.0 Gy/min
Constant dose rate
: Grafting % increased slowly with increase in total irradiation dose at initial radiation & increased rapidly
Initial stage [Chain initiation]
: Slow increase in grafting %, Then, it will slowly increase rapidly.
Beyond 600 Gy
: Solution viscosity increased & Grafting % peaked & varied slightly with increase irradiation dose.
3.3.2. Radiation dose rate
Grafting percentage was lower when: Irradiation dose rate was higher at the same total irradiation dose
3.3.3. Monomer concentration
Higher the presence of acrylamide concentration in polymerization medium, provide GREATER availability of acrylamide molecules with which chitosan macroradicals could react
RESULT: in Higher grafting percentage
3.4. Flocculation ability evaluation
THE FLOCCULATION ABILITY WAS EXAMINED WITH KAOLIN SUSPENSIONS OF 0.25% (w/v) at pH 4.0, 7.0 and 10.0
The flocculation ability of chitosan, polyacrylamide (PAM), chitosan-g-PDMC with Grafting percentage of 64%
chitosan, polyacrylamide (PAM), chitosan-g-PDMC had better flocculation ability than PAM
The flexible polyacrylamide chain grafted onto the rigid chitosan backbone increased the flocculant flexibility that favored the binding intensity between flocculants and colloids.
Then, the re-dispersion resulting from the competition of bridging could be avoided to some extent
The flocculation ability of chitosan-g-PAM with with different grafting percentages of 56% and 166%
chitosan-g-PAM showed excellent flocculation ability under acidic (pH 4.0) and alkaline conditions (pH 10.0).
The flocculation window of chitosan-g-PAM was broader than that of chitosan-g-PDMC, attributed to the fact that the re-dispersion resulted from the charge reversion in addition to the competition of bridging, when chitosan-g-PDMC was used as the flocculant.
graft copolymer, chitosan-g-PAM had a broader flocculation window than chitosan
3.5. Settling rate of flocs
The settling process of the kaolin floccules over time treated by various flocculants
the kaolin floccules from the suspension treated by the graft copolymer with a higher grafting percentage settled more rapidly
the graft copolymer with a higher grafting percentage was in favor of bridging among the kaolin suspended colloids.
BUT the suspension treated with chitosan observed under alkaline conditions has no clear interface between water and solid. BECAUSE chitosan had negligible flocculation ability in this case.
METHOD
Characterization of the grafted copolymer
XRD patterns were obtained with an X-ray diffractometer using graphite
monochromatized Cu Ka radiation
TGA of chitosan and the graft copolymer was performed using a thermal analyzer
Infrared spectra were recorded with an FTIR spectrometer using a potassium
bromide disc technique
Jar test
The transmittance of supernatant was measured with a spectrophotometer
The solution was settled for 5 min
The suspensions were immediately stirred
The flocculants were added into each of six 500 ml beakers with kaolin
suspension
Graft copolymerization of acrylamide onto chitosan
The solutions were placed in Pyrex glass vessels and irradiated
The sample solutions were precipitated in acetone and separated by filtration
The homopolymer formed in the reaction was removed through Soxhlet extraction
using ethanol-water for 24 h
The grafted copolymer was then dried in a vacuum oven at 50 C until a constant
weight was obtained
The solutions were deoxygenated by nitrogen bubbling for 30 min
The grafting percentage was calculated
Chitosan and acrylamide solution were prepared with 1.0% acetic acid solution
Settling rate
The flocculant was added into the cylinder with 100 ml kaolin suspension
The cylinder was inverted for 10 times
The height of the interval between the surfaces of the supernatant and the settling
solid bed was recorded over time
Material
Acrylamide, acetone, ethanol, glycol and acetic acid
Doubly distilled water
Chitosan
INTRO
Chitosan flocculent efficiency can decrease when it dissolved in only acidic solution - thus, chitosan modification must be done
Flocculent ability of the copolymer could be improved through grafting
Applications for wastewater treatment and sludge dewatering
Polyacrylamide (PAM), as an efficient flocculant, has been extensively used for
wastewater treatment and sludge dewatering
Chitosan is biodegradable and non-toxic
But, it is non-biodegradable, and has toxic residual
monomers,
Acrylamide was used as the grafted monomer
Chitosan, was modified to prepare an efficient flocculant using a
grafting method in acid– water solution
At the end, the jar test results demonstrated the superiority of chitosan-g-PAM over chitosan
and PAM as an efficient flocculant
Group 3:
AKMAL SYAHMI BIN HASLAN (A174610)
FARAH HANIM SYAHIRAH BINTI AYOB (A174668)
NUR' ATIKAH BINTI ZAKARIA (A174803)
NUR FATIN HANANI BINTI RAZALI (A174838)
NAZIRAH BINTI MOHD NAZRI RETHINASAMY (A174936)
MOHAN A/L KUMARAN (A175012)
NUR SYAFIQAH BINTI ABDUL JALAL (A175085)
Reference: Wang, J. P., Chen, Y. Z., Zhang, S. J., & Yu, H. Q. (2008). A chitosan-based flocculant prepared with gamma-irradiation-induced grafting. Bioresource Technology, 99(9), 3397–3402.
https://doi.org/10.1016/j.biortech.2007.08.014