Waste and Biomass Valorization
span compressive (SCT) strength was measured according to DIN 54518:2004 [64], the tensile strength according to ISO 1924-2:2009 [65] and the tear strength according to ISO 1974:2012-09 [66]. All instruments used for aforementioned measurements were manufactured by FRANK-PTI Gmbh (Birkenau, Germany). The indices were calculated according to TAPPI T 220 [67].
∑ ( n i l i ) ∑ n i
(2)
L ( n ) =
2 i
∑ ( n i l
)
(3)
L ( lw ) =
∑ n i
n i = number of fibers in the specified fiber class, l i = fiber length in specified class [mm]
Results and Discussion
− 1 ) ∗ 100%
Curl i = (
Lc i Lp i
(4)
Fiber Morphology
∑ ( n i ∗ Curl i ) ∑ n i
Key parameters of the fiber morphology of the waste MDF fibers following steam refining treatments of different sever- ity are presented in Table 2 and compared to recycled pulp samples from industrial corrugated paperboard producers. The SR-MDF (B) fibers show widths of 30.1 μm to 31.8 μm and length weighted fiber lengths of 0.87 mm to 1.00 mm in comparison to widths of 24.1 μm to 25.0 μm and length weighted lengths of 0.72 mm to 0.86 mm of the SR-MDF (A) fibers. These differences support the presumption of the different ratios of softwood and hardwood fibers in the cor- responding samples, as softwood fibers are usually longer and wider than hardwood fibers [55, 68]. A more severe steam treatment led to a slight reduction in fiber length, while the fiber width and the amount of fines material was mostly unaffected for both SR-MDF sample sets. However, differences in behavior between the SR-MDF sample A and B can be seen in the amount of fiber kink and curl measured. While the amount of fiber curl and kinks were mostly unaffected for the SR-MDF (B) sample, except for a slight increase at the very highest severity degree, a distinct increase in fiber curl and kinks can be observed for
(5)
Curl ( n ) =
Lc i = true contour fiber length [mm], Lc p = projected fiber length [mm], Curl i = Fiber curl of specified fiber class [%]
( n 10 − 20 ◦ + 2 ∗ n 21 − 45 ◦ + 3 ∗ n 46 − 90 ◦ + 4 ∗ n 90 + ◦ ) Lc i
Kink i =
(6)
∑ ( n i ∗ Kink i ) ∑ n i
(7)
Kink ( n ) =
n x-y = Numbers of kinks with a kink angle between x° to y°, Kink i = Number of kinks of specified fiber class [1/mm]. Laboratory paper sheets of about 75 g/m 2 were produced with a Rapid-Köthen sheet forming machine (FRANK-PTI, Birkenau, Germany) as described by ISO 5269-2:2004 [62] and conditioned for at least 24 h at (23 ± 1) °C and (55 ± 2) % relative humidity before physical testing. The brightness was measured according to TAPPI T525 [63] with an ELREPHO 450X from Datacolor (Rotkreuz, Switzerland). The short
Table 2 Influence of the treatment severity on the fiber morphology of the steam treated waste MDF samples in comparison to morphological characteristics of recycled pulp
Sample
Severity L(n)
L(lw) (mm)
Width Fines
Fiber Curl
Kink index
(Log R 0 )
(mm)
(μm)
(%)
(%)
(1/m)
SR-MDF (A)
2.5 2.8 3.1 3.4 3.7 4.0 2.5 2.8 3.1 3.4 3.7 4.0
0.54 0.86 0.46 0.75 0.47 0.76 0.49 0.78 0.48 0.76 0.46 0.72 0.56 0.96 0.55 1.00 0.56 0.96 0.53 0.95 0.50 0.93 0.50 0.87 0.53 1.09 0.55 1.09
25.0 24.7 24.2 25.0 24.8 24.1 30.3 30.1 31.6 30.9 30.8 30.1 22.1 20.7
5.0 8.0 7.1 6.5 6.7 6.9 5.4 6.1 5.3 6.3 7.8 6.7 5.3 5.1
6.2 6.2 6.9 7.4
356 306 365 434 603 723 296 241 265 256 269 381
10.0 11.4
SR-MDF (B)
5.2 5.0 4.8 5.0 5.3 5.9
RP RP
#1 – #2 –
20.1 16.9
1528 1062
1 3
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