The base paper used for the tests was characterized by the initial value of Young's modulus at the level of 11,650 MPa. The coating of the paper caused an increase or decrease in the value of the considered parameter, depending on the grammage of the coating. The use of rods with numbers 4 - 7 contributed to a decrease in Young's modulus by 7 ÷ 14%. On the other hand, for rods 8 – 15 an increase in the parameter by 2 ÷ 12% was observed. Importantly, the increase in the coating grammage caused a proportional increase in Young's modulus (Tab. 2).
Table 2. Tensile properties of paper Mayer Rod number V T b V T W N/m Nm/g
E *
E b
E w
F B
W T b J/m 2
W T W
H T
N
%
J/g
kN/m Nm/g
MPa 9990 (237) 10790 (137) 10420 (230) 10790 (137) 11850 (276) 12170 (291) 12650 (237) 13070 (546)
13700 (380) 14870 (445) 14840 (320) 14870 (445) 16250 (519) 16960 (366) 17520 (368) 18570 (492)
105,9 (3,0) 113,8 (3,4) 110,5 (2,5) 113,8 (3,4) 117,4 (3,7) 123,2 (2,8) 130,3 (2,8) 133,2 (3,3)
136,4 (4,9) 145,4 (4,7) 145,6 (2,8) 145,4 (4,7) 159,6 (4,8) 166,5 (5,4) 172,1 (4,7) 183,0 (6,3)
2,76 (0,17) 2,75 (0,12) 2,77 (0,11) 2,75 (0,12) 2,68 (0,10) 2,78 (0,11) 2,89 (0,09) 2,83 (0,15)
232,0 (20,4) 249,7 (19,1) 250,4 (16,3) 249,7 (19,1) 261,6 (17,3) 293,5 (18,1) 322,6 (19,6) 321,4 (25,4)
1,79 (0,16) 1,91 (0,15) 1,87 (0,12) 1,91 (0,15) 1,91 (0,12) 2,13 (0,13) 2,40 (0,15) 2,31 (0,18)
1098 (26) 1187 (15) 1145 (25) 1187 (15) 1303 (29) 1339 (31) 1394 (26) 1438 (61)
8487 (194) 9056 (99) 8545 (173) 9056 (99) 9499 (216) 9729 (228) 10360 (217) 10316 (424)
4
5
6
7
8
9
12
15
Note: Extended deviation are given in brackets. CONCLUSIONS
On the basis of conducted research, it was found that the basic functional properties of paper depend on the pigment-adhesive mixture applied as a coating on the paper. The characteristics of the Cobb water absorption curve, as well as the results of tensile and structural parameters, indicate that the highest hydrophobicity, surface smoothing, and highest mechanical properties are achieved in papers with the highest coating weight. Interestingly, not all coatings increase the tensile parameters of the paper. The decrease in strength was observed for samples with the thinnest coatings, which may be caused by the uneven distribution of the mixture on the surface, resulting in local weaknesses in the paper structure. Therefor, the results of the test, suggest that the most effective migration of binding agents takes place in the thickest coatings. This leads to a homogeneous distribution of the binders in the dry film. Thus, not only increasing the number of coating agents but also controlling the uniformity of the formed coating structure is decisive in improving the performance of coated papers. Acknowledgment. This work was financially supported by the National Centre of Research and Development in Poland (Project NumberPOIR.01.01.01-00-0084/17 and POIR.04.01.04-00-0022/18). The authors are also grateful to Natural Fibers Advanced Technologies for allowing access to the company's R&D laboratory.
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