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

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

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.

3.2: Characterization of the graft copolymer

3.2.1: FTIR spectrum

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

METHOD

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

Characterization of the grafted copolymer

Jar test

Graft copolymerization of acrylamide onto chitosan

Settling rate

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

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

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

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

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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.

3.3.3. Monomer concentration

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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%

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).

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 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.

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.

graft copolymer, chitosan-g-PAM had a broader flocculation window than chitosan

Group 3:

  1. AKMAL SYAHMI BIN HASLAN (A174610)
  2. FARAH HANIM SYAHIRAH BINTI AYOB (A174668)
  3. NUR' ATIKAH BINTI ZAKARIA (A174803)
  4. NUR FATIN HANANI BINTI RAZALI (A174838)
  5. NAZIRAH BINTI MOHD NAZRI RETHINASAMY (A174936)
  6. MOHAN A/L KUMARAN (A175012)
  7. 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