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Table 1 Paper composite formulation a
The intrinsic viscosity was determined in dilute solutions using eqn (4), where h sp / c is the reduced viscosity and k h is the Huggins constant.
No Sample name Wood pulp bres (%) CA bres (%) KA bres (%)
1 HBKP 2 CA25 3 CA50 4 CA75 5 KA25 6 KA50 7 KA75
100
0
0 0 0 0
2 c
(4)
h sp / c = [ h ] + k h [ h ]
75 50 25 75 50 25
25 50 75
Then, the obtained intrinsic viscosity was used to estimate the molecular weight of alginate using the Mark – Houwink equation (eqn (5)), as follows:
0 0 0
25 50 75
[ h ] = KM v a
(5)
a CA: commercial alginate and KA: kelp alginate.
K and a values depend on the polymer and solvent-temperature systems. The study by Clementi et al. 23 proposed empirical relationships for [ h ] and the average molecular weight ( M w ) so the eqn (6) becomes:
was prepared in the spinning process from commercially available sodium alginates fabricated into bres for compar- ison. In contrast, seaweed calcium alginate bres and sargassum calcium alginate bres were both alginate samples obtained from previous samples and fabricated into bres. 2.6 Preparation of laboratory sheets Wood pulp bres and calcium alginate bres were used in the formation of laboratory sheets. A total of 27 g of dry HBKP was weighed and immersed in water for 1 day. Then, the wet pulp was dispersed well with a disintegrator for 5 min. The dis- integrated pulp was sieved, collected, and subjected to beating to enhance the mechanical strength of the laboratory sheets, by swelling and increasing the exibility of bres. In the beating process, pulp was put into a mill house of a PFI mill and rotated 5000 times. Subsequently, 7.8 L water was then added to the beaten pulp, and the pulp was dispersed well with a mixer in a bucket. Consequently, a nal pulp concentration of 0.15% was reached, and then 800 mL of pulp suspension was taken per sheet. To obtain a composite of paper, we designed the exper- iment by adding calcium alginate bres, as shown in Table 1. The wet sheets were dried at RT for 24 h. Finally, the laboratory sheets were prepared for further evaluation. 2.7 Capillary viscometry: viscosity and molecular weight The kinematic viscosity ( v ) was determined using a Cannon- Fenske routine viscometer with a 0.1 M NaCl aqueous solu- tion as a solvent. For each sample, ve measurements were made at 25 °C ± 0.1 °C according to Torres et al. 22 Alginate solutions (30 g L − 1 ) were prepared by stirring at RT for 4 h. A er measuring the absolute viscosity of the solvent ( h 0 ) and alginate solutions ( h s ), the relative viscosity ( h r ) and speci c viscosity ( h sp ) were calculated according to eqn (1) and (2):
a 0.984 ,
(6)
[ h ] = 0.023 M v
where [ h ] is the intrinsic viscosity given in dL g − 1 and M in kilodaltons. The M w values for alginates from L. japonica and S. polycystum were estimated from the intrinsic viscosity data.
2.8 Analysis of functional properties by Fourier transform infrared spectroscopy (FTIR) FTIR spectra of sodium alginate and paper sheet composites were recorded using a FTIR spectrometer (FT/IR-6100, JASCO Corporation, Japan) combined with an ATR (PRO ONE PKS-Z1, JASCO Corporation, Japan) spectrometer with a Ge prism (PKS- G1, JASCO Corporation, Japan) as a reference in the range of 500 – 4000 cm − 1 to examine the possible changes in functional groups induced by various treatments. 2.9 Analysis of surface morphology by eld emission scanning electron microscopy (FESEM) The surface morphologies of the calcium alginate bres and paper composites were analysed using FESEM (SU8020, Hitachi, Japan) with an accelerating voltage of 5 kV. All samples were coated with platinum (Pt) through sputtering for electro- conductivity before observation.
(1)
h r = h s / h 0
(2)
h sp = h r − 1
The intrinsic viscosity is a measure of the hydrodynamic volume occupied by the macromolecule at in nite dilution in a speci c solvent at a given temperature and is de ned by the Huggins equation (eqn (3)) as follows: ½ h ¼ lim c / 0 h sp c (3)
Fig. 3 A paper frame used for gluing a single fi bre specimen.
602 | RSC Sustainability , 2025, 3 , 599 – 610
© 2025 The Author(s). Published by the Royal Society of Chemistry
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