Effects of Recycled Fiber Fines on Hand Sheet Properties of Different Unbeaten and Beaten Pulps

In this study, 5, 10, and 15 % secondary fines of recycled pulp were added to unbeaten and beaten (28 ºSR) samples of recycled pulp, Turkish Calabrian pine (Pinus brutia Ten.) kraft pulp, and European aspen (Populus tremula L.) kraft pulp. The effects of the addition of fiber fines on hand sheets properties were evaluated. The addition of fiber fines to the unbeaten pulps improved the strength properties of hand sheets. The roughness of hand sheets was also decreased with the addition of fines. When fiber fines were added to the beaten pulps, the type of pulp strongly affected the paper strength properties. The strength properties of beaten pulps of Turkish Calabrian pine and European aspen were decreased with the addition of fiber fines, while the strength properties of beaten pulps of recycled pulp were increased. On the other hand, the air permeance of unbeaten and beaten samples was decreased with the addition of fiber fines. Consequently, the addition of fines to unbeaten and beaten pulps had a more pronounced effect on European aspen kraft pulp and recycled pulp than on Turkish Calabrian pine kraft pulp. Also, the strength of paper made of unbeaten recycled pulp with the addition of 15 % fines was higher than that of fines-free beaten recycled pulp.

. The diffi culty in dewatering produces a deceleration in the manufacturing process (Htun and de Ruvo, 1978;Taipale, 2010), causing an increase in the amount of energy required to dry the paper (Chen et al., 2009).
The effect of fi nes on paper properties of mechanical pulps (Mohlin, 1977; Moss and Retulainen, 1997;Lu, 1999;Luukko and Paulapuro, 1999;Rundlöf, 2002;Vainio et al., 2007;Asikainen et al., 2010;Chen et al., 2013;Moberg et al., 2014) and chemical pulps (Kibblewhite,1972;Lobben, 1977;Htun and de Ruvo, 1978;Hartman, 1984;Przybysz and Czechowski, 1985;Retulainen et al., 1993Retulainen et al., , 2002Retulainen, 1997;Ferreira et al., 2000;Krogerus et al., 2002a;Taipale et al., 2010) have been extensively studied. However, the infl uences of the addition of fi nes on the paper properties of the recycled pulps have seldom been reported. In general, fi nes (primary and secondary fi nes) of the recycled pulps are considered as undesirable for the strength properties, because the fi nes are produced from dried and hornifi ed fi bers. Mancebo and Krokoska (1985) noted that the fi nes of recycled pulp have a negative impact on paper strength as they act as fi ller material. The fi nes indicate the loss of bonding ability due to hornifi cation, and it is claimed that the effect is irreversible even with refi ning. Also, Szwarcsztajn and Przybysz (1977) found that fi nes and fi bers obtained from recycled paper hornifi ed, causing the loss of the paper strength. Quite the contrary, Hawes and Doshi (1986) noted that fi nes of recycled paper are effective in increasing the strength of hand sheets made from recycled paper. The recycled fi nes act like virgin fi nes, so the removal of fi nes causes a reduction in the bonding index (Htun and de Ruvo, 1978; Klungness and Sanyer, 1981;Rushdan, 2005). Recently, the effect of fi ne content and quality on the recycled chemical pulps was studied by Lee et al., (2011).
In this study, the effects of the addition of secondary fi nes to recycled pulp (5, 10, and 15 %) on hand sheet properties were evaluated. Three types of pulp were used, recycled pulp, Turkish Calabrian pine (Pinus brutia Ten.) kraft pulp, and European aspen (Populus tremula L.) kraft pulp, in order to determine the relationship between the addition of fi nes and the type of pulp. Also, two types of freeness level were used, unbeaten pulp and 28 ºSR pulp, in order to investigate the effect of fi nes on pulps at different freeness levels.

MATERIJALI I METODE
Unbleached recycled pulps used in this study were obtained from Oyka pulp mill in Turkey. Turkish Calabrian pine and European aspen wood samples were obtained from Bartin province of Turkey. The wood samples were debarked and chipped to 3 cm × 1.5 cm × 0.5 cm size for kraft pulping. The air dried wood chips were stored in dry conditions. The kraft cooking conditions of both species are given in Table 1.
Cooking was carried out in a 15-L electrically heated laboratory cylindrical-type rotary digester. After

UVOD
The fi nes are defi ned as the cellulosic fi ber fraction of a fi ber suspension which can pass through a 200 mesh (200 wires per inch) screen with a 14.5 % open area and 76.2 μm diameter in Bauer McNett classifi er (Meyers and Nanko, 2005). Therefore, the fi nes are sometimes named the P200 (Taipale, 2010). Also, the maximum and minimum fi ne length is detected as 0.2 mm and 0.072 mm, respectively (Meyers and Nanko, 2005). On the other hand, fi nes are extensively evaluated as all particles smaller than wood fi bers present in the furnish (Krogerus et al., 2002a). In accordance with this defi nition, fi nes may consist of various particles such as parts of wood cells, inorganic pigments and fi llers, colloidal resins and latex, salt crystals, precipitates, deposits, etc. (Taipale, 2010).
Fines are generally categorized as primary and secondary fi nes. Primary fi nes are present in the pulp prior to refi ning, whereas secondary fi nes arise during refi ning. Primary fi nes consist mainly of ray cells, parenchyma cells and middle lamella lignin. (Bäckström et al., 2008). Primary or secondary layers of cell wall are delaminated during refi ning, and they became detached from the fi bers. So-formed secondary fi nes incline to be slender and fl exible (Chen et al., 2009).
Primary and secondary fi nes contribute differently to the mechanical properties of paper (Htun and de Ruvo, 1978). For a given fi nes content, the effect of secondary fi nes on strength properties of the pulp are more pronounced than those of primary fi nes (Hawes and Doshi, 1986;Bäckström et al., 2008). Primary fi nes have a higher lignin content than kraft pulp fi bers (Retulainen et al., 2002). Secondary fi nes come mostly from the fi ber surface during refi ning, and they have a higher lignin content compared to the fi bers, but lower compared to the primary fi nes (Lindström and Nordmark, 1978). Secondary fi nes have about twice as much fi brils as primary fi nes (Krogerus et al., 2002b). In chemical pulp, the cellulose and hemicellulose content of fi nes is higher than in the fi ber fraction (Taipale, 2010). Also, the crystallinity of fi nes was lower compared to the long fi ber fraction (Waterhouse and Omori, 1993).
The term fi nes is extensively used in the papermaking process, and fi nes have a signifi cant infl uence on the behavior of the wet web and on all the properties of the fi nal sheet (Bäckström et al., 2008). Fines can help to fi ll in the voids between fi bers in the paper structure. Fibrillar fi nes can bring fi bers into closer contact with each other during the consolidation and drying of sheet (Johansson, 2008). In other words, fi nes increase inter-fi ber bonding by acting as a bridge between fi bers (Bäckström et al., 2008;Retulainen et al., 2002;Silveira et al., 1996). If there are more bonds, the segments between bonds are shorter and there are fewer free loops (Retulainen et al., 1993). Thus, a denser, stronger, and more uniform product is formed (Lin et al., 2007 The secondary fi nes were acquired by refi ning the recycled pulps in a Valley beater for 7 h with loading according to TAPPI T 200. The refi ned pulp was fractionated in a Bauer-McNett classifi er (TAPPI T 233) into fi ve fractions: R30, R50, R100, R200, and R300 mesh. Fines passing through a 200 mesh screen and retained by a 300 mesh were used as paper additive. The fi ber morphology of the different pulps and secondary fi nes was determined with light microscope. Some pulp properties and fi ber morphology of different pulps and fi nes are given in Table 2.
Different mixtures of unbeaten and beaten pulps of different fi bers (Turkish Calabrian pine, European aspen, and recycled fi ber) and secondary fi nes were used to prepare hand sheets and to determine the effect of fi nes on paper strength properties. Four levels of fi nes were used: 0, 5, 10, and 15 % of the dry weight of the fi bers (Table 3). More than 15 % fi nes were not used due to diffi culty in dewatering and drainage during papermaking. Freeness of fi nes added pulps (ISO 5267-1) was also determined. The hand sheets (70 g/ m 2 ) made by a Rapid-Kothen Sheet Former (ISO 5269-2) were conditioned (TAPPI T 402). Tensile index (ISO 1924-3), burst index (TAPPI T 403), tear index (TAPPI T 414), roughness (ISO 8791-2), apparent density (TAPPI T 220), and air permeance (ISO 5636-3) of the hand sheets were also determined.
The data of hand sheet properties were subjected to analysis of variance (ANOVAs) and Duncan test at a 0.05 probability level. The same lower case letter in all fi gures denotes that the difference in the average values

Pulp freeness 3.1. Sposobnost odvodnjavanja celuloze
Drainage, an important parameter in the paper manufacturing, restricts the production effi ciency of a paper machine (Norell et al., 1999). Important factors infl uencing wetness end drainage are pulp composition, average fi ber length, fi ber length distribution, fi nes content, charge level on the stock, and degree of stock hydration (Paradis et al., 2002). Fines have a detrimental effect on dewatering of the pulp suspension due to their high water holding capacity (Htun and de Ruvo, 1978;Hartman, 1984 Lu (1999) noted that the pulp containing 40 % of fi nes drains 10 times more slowly than fi nes-free pulp. Kibblewhite (1972) reported that the pulp freeness strongly affected the quality and quantity of fi nes. Seth (2003) noted that pulp freeness drastically decreases with the addition of fi nes. The effect of the addition of fi nes on pulp freeness of unbeaten and beaten pulps is given in Table 4. The pulp freeness was decreased with increasing fi nes ratio.

Vlačni indeks
Tensile index is one of the basic strength properties of paper. The effect of the addition of fi nes on tensile index of the unbeaten and beaten pulps was more pronounced in European aspen kraft pulp and recycled pulp than in Turkish Calabrian pine kraft pulp ( Figure  1). On the other hand, the effect of the addition of fi nes on tensile index of unbeaten pulps was more prominent than of beaten pulps. The effect was more pronounced at a higher level of addition. Lobben (1977) reported that the fi nes of chemical pulps had a considerable effect on strength properties depending on fi ber type and freeness level of pulp. The effect of the addition of fi nes was greater for a eucalypt kraft pulp than for a pine kraft pulp. Also, the effects were more pronounced in unbeaten pulps of long fi ber fraction.
As can be seen in Figure 1, the addition of 5, 10, and 15 % secondary fi nes to Turkish Calabrian pine unbeaten kraft pulps resulted in the increase in tensile index of 13.14 %, 20.22 %, and 29.68 %, respectively (p<0.05). The addition of 5, 10, and 15 % secondary fi nes to unbeaten European aspen kraft pulp resulted in the increase in tensile index of 55.22 %, 60.49 %, and 85.07 %, respectively. The addition of 5, 10, and 15 % secondary fi nes to recycled unbeaten pulps resulted in the increase in tensile index of 16.29 %, 36.80 %, and 43.49 %, respectively (p<0.05). Tensile index did not deteriorate with increasing addition of fi nes, and the more fi nes in hand sheet caused better bonding. These fi ndings can be attributed to the increase in fi ber-fi ber bonding area due to the fi lling of inter-fi ber gaps in the paper structure by fi nes. On the other hand, the addition of fi nes to fi ber suspension results in the decreased average fi ber length. However, tensile index of hand sheets did not decrease. This may be due to increasing fi ber-fi ber bonding thanks to the presence of fi nes, which overcompensated for the impaired tensile index caused by the decreasing average fi ber length.
Previous studies revealed that the recycled fi nes act like virgin fi nes, causing an increase in the bonding index (Hawes and Doshi, 1986; Htun and de Ruvo, 1978; Klungness and Sanyer, 1981;Rushdan, 2005). In this study, the recycled fi nes did not act as a fi ller as found in other studies (Szwarcsztajn and Przybysz, 1977;Manchebo and Krokoska, 1985). Asikainen et al., (2010) noted that tensile index increased with the addition of 10 % and 20 % primary fi nes to CTMP from 22.5 Nm/g to 26.8 Nm/g and 31.0 Nm/g, respectively. Retulainen (1997)  In the beaten samples of Turkish Calabrian pine and European aspen kraft pulp, the addition of fi nes had not a statistically signifi cant effect on tensile index of hand sheets (p>0.05) (Figure 1). The tensile index of recycled beaten pulps increased with the addition of 5, 10, and 15 % of secondary fi nes by 10.96 %, 22.47 %, and 34.47 %, respectively (p<0.05). These results can be attributed to better response to beating of virgin (fl exible) fi bers than recycled (stiff) fi bers due to differences in their fi ber morphology. Tensile index of has also been reported by several authors (Mohlin, 1977;Hartman, 1984;Lee et al., 2011). Quite the contrary, tear index decreased with the addition of fi nes (Waterhouse, 1994). Tear index of Turkish Calabrian pine unbeaten kraft pulp decreased with the increasing addition of fi nes, while it increased for European aspen unbeaten kraft pulp and unbeaten recycled pulp (Figure 2). This result may be explained as follows. Tear index depends on several factors, including fi ber length, wall thickness, inter-fi ber bonding, fi ber strength, etc. Fines contribute to tear index by increasing inter-fi ber bonding due to their good fl exibility and large surface area. Thus, tear index of short fi ber European aspen and recycled pulp samples was increased with the addition of fi nes. As fi nes content increased, the average fi ber length and wall thickness decreased. Also, the larger gaps between long fi bers of Turkish Calabrian pine were not suffi ciently fi lled by fi nes, resulting in lower inter-fi ber bonding than samples without fi nes. Hence, tear index of Turkish Calabrian pine sample was decreased with the addition of fi nes.
In beaten pulps, tear index of Turkish Calabrian pine and European aspen kraft pulps decreased with the addition of 5, 10, and 15 % secondary fi nes by 6.37 %, 11.67 %, 11.14 % and 4.15 %, 10.65 %, 11.95 %, respectively (p<0.05) (Figure 2). Quite the contrary, the addition of 5, 10, and 15 % secondary fi nes to recycled unbeaten pulp resulted in the increase in tear index of 5.39 %, 10.56 %, and 4.46 %, respectively (p<0.05). These results showed that the effect of fi nes addition on tear index was more prominent than beating. For example, tear index of recycled unbeaten pulp was increased by beating up to 28 ºSR from 4.03 mNm 2 /g to 4.26 mNm 2 /g. However, with the addition of 15 % fi nes, tear Turkish Calabrian pine and European aspen pulp samples was increased with beating to 28 ºSR by 110.97 % (from 39.12 Nm/g to 82.53 Nm/g) and 134.70 % (from 35.33 Nm/g to 82.92 Nm/g), respectively, while in recycled pulp samples this increase was only 34.15 % (from 25.71 Nm/g to 34.49 Nm/g). The lower tensile index increase in beaten recycled pulp was compensated with the addition of fi nes (Figure 1). On the other hand, tensile index of unbeaten recycled pulp (36.89 Nm/g), with the addition of 15 % fi nes, was higher than that of fi nes-free beaten recycled pulp (34.49 Nm/g).

Tear index 3.3. Indeks cijepanja
The effect of the addition of fi nes on tear index of hand sheet depends on the type of pulp and the amount of fi nes added. Tear index of Turkish Calabrian pine unbeaten kraft pulps decreased with the addition of 5, 10, and 15 % secondary fi nes by 11.17 %, 17.04 %, and 27.99 %, respectively (p<0.05). Quite the contrary, tear index of European black pine unbeaten kraft pulp and recycled unbeaten pulp increased with the addition of 5, 10, and 15 % secondary fi nes by 19.25 %, 22.99 %, 25.93 % and 12.40 %, 17.61 %, 9.42 %, respectively (p<0.05). These results showed that the addition of fi nes had a positive effect on tear index of hand sheets obtained from short fi bers compared to long fi bers ( Figure 2). This result is consistent with previous work (Hawes and Doshi, 1986), which showed that tear index increased with the addition of 20 % secondary fi nes to recycled pulp from 8.7 mNm 2 /g to 9.95 mNm 2 /g. Ferreira et al., (2000) noted that tear index increased from 9.5 mNm 2 /g to 10.2 mNm 2 /g when fi nes were removed from fi ber suspension. The positive correlation between tear index and fi nes addition  index of recycled unbeaten pulp was increased from 4.03 mNm 2 /g to 4.41 mNm 2 /g. On the other hand, when 15 % fi nes were added to unbeaten recycled pulp (4.41 mNm 2 /g), tear index was higher than that of fi nes-free beaten recycled pulp (4.26 mNm 2 /g).

Indeks pucanja
In unbeaten pulps of all types of pulp, the addition of fi nes caused an increase in burst index ( Figure  3). The highest increase in burst index was determined in European aspen kraft pulp. The addition of 5, 10, and 15 % secondary fi nes to Turkish Calabrian pine kraft pulp resulted in the increase in burst index of 14.34 %, 30.43 %, and 42.60 %, respectively (p<0.05). The increase of burst index in European aspen kraft pulp and recycled pulp was found to be 26.73 %, 57.75 %, 67.91 % and 10.48 %, 33.87 %, 37.09 %, respectively (p<0.05). The burst index of hand sheets increased linearly with increasing proportion of fi nes (Figure 3). These fi ndings can be ascribed to increasing inter-fi ber bonding due to higher surface area of fi nes than fi bers. The surface area of fi nes ranges from 10 to 50 m 2 /g, while the surface area of fi bers is around 1 m 2 /g (Retulainen et al., 1993). Hawes and Doshi (1986) reported that burst index increased with the addition of 20 % secondary fi nes to recycled pulp from 1.39 kPam 2 /g to 3.86 kPam 2 /g. Ferreira et al., (2000) noted that burst index decreased from 6.9 kPam 2 /g to 5.0 kPam 2 /g when fi nes were removed from fi ber suspension. Other authors reported that burst index increases with the addition of fi nes (Mohlin, 1977 In beaten pulps, the addition of 5, 10, and 15 % secondary fi nes to Turkish Calabrian pine kraft pulp resulted in burst index loss of 1.93 %, 6.21 %, and 3.64 %, respectively (p<0.05). Quite the contrary, the addition of secondary fi nes to European aspen kraft pulp resulted in a statistically insignifi cant increase of burst index, (p>0.05). On the other hand, an increase in burst index of 12.12 %, 20 %, and 43.03 %, respectively (p<0.05), was observed in recycled pulp with the addition of 5, 10, and 15 % secondary fi nes. In beaten pulps, the relationship between burst index and fi nes addition is drastically different depending on the type of pulp (Figure 3). These results can be explained by increased inter-fi ber bonding that acts as a bridge of fi nes between hornifi ed and stiff recycled fi bers. Thus, the strength of paper made from recycled fi bers with low bonding capacity increases with the addition of fi nes. Along with the beating, the decrease in fi ber length and the improved fi ber fl exibility and plasticity increase the bonded area between fi bers. Thus, the paper structure became more compact and burst index increased. Also, the mobility of fi nes may be lower in the wet sheet of collapsed, swollen, and externally fibrillated fi bers compared to the more open structure in a wet sheet of unbeaten fi bers (Hartman, 1984).
In the virgin pulp samples, freeness level of pulp had a more signifi cant effect on burst index than the fi nes content. For example, burst index of Turkish Calabrian pine kraft pulp was increased with beating up to 28 ºSR from 2.30 kPam 2 /g to 4.67 kPam 2 /g. However, burst index of Turkish Calabrian pine unbeaten kraft pulp was increased from 2.30 kPam 2 /g to 3.28 kPam 2 /g with the addition of 15 % fi nes. In the recycled pulp sample, the effect of freeness level of pulp and fi nes addition on burst index was similar. Burst index of recy-    cled pulp was increased with beating up to 28 ºSR from 1.24 kPam 2 /g to 1.65 kPam 2 /g. However, burst index of recycled unbeaten pulp was increased from 1.24 kPam 2 /g to 1.70 kPam 2 /g with the addition of 15 % fi nes.

Prividna gustoća
As the addition of fi nes increased, the apparent density of the hand sheets increased linearly as shown in Figure 4. The highest increase in apparent density was determined in Turkish Calabrian pine kraft pulp. The addition of 5, 10, and 15 % secondary fi nes to Turkish Calabrian pine kraft pulp resulted in an increase in apparent density of 3.51 %, 7.02 %, and 12.28 %, respectively (p<0.05). An increase in apparent density of 3.13 %, 4.68 %, 7.81 % and 7.55 %, 7.55 %, 11.32 %, respectively (p<0.05), was determined in European aspen kraft pulp and recycled pulp. This is consistent  with previous work (Lu 1999), which showed that the sheet density increased with the addition of 20, 30, and 40 % fi nes to mechanical pulp from 0.372 g/cm 3 to 0.511 g/cm 3 , 0.555 g/cm 3 and, 0.563 g/cm 3 , respectively.
Fines cause an increase in sheet density by fi lling the voids between the fi bers. In addition, Hawes and Doshi (1986) noted that the sheet density increased with the addition of 20 % secondary fi nes to recycled pulp from 0.549 g/cm 3 to 0.629 g/cm 3 . On the other hand, Ferreira et al., (2000) reported that sheet density decreased when fi nes were removed from fi ber suspension from 0.767 g/cm 3 to 0.708 g/cm 3 . The positive correlation between fi ne addition and sheet density has also been reported by other authors (Mohlin, 1977;Hartman, 1984;Hawes and Doshi, 1986;Waterhouse and Omiri, 1993;Lu, 1999;Bäckström et al., 2008;Lee et al., 2011;Moberg et al., 2014).
In beaten pulps of all types of pulp, the addition of fi nes had a statistically insignifi cant effect (p>0.05) on apparent density of hand sheets (Figure 4). These results indicated that the freeness level of pulp is more important for the apparent density than the content of fi nes. For example, apparent density of European aspen kraft pulp was increased with beating up to 28 ºSR from 0.64 g/cm 3 to 0.82 g/cm 3 . Whereas, apparent density of European aspen kraft pulp with the addition of 15% fi nes was increased from 0.64 g/cm 3 to 0.69 g/cm 3 .

Hrapavost
Hand sheet roughness was signifi cantly affected by fi nes. In unbeaten pulps of all types of pulp, roughness of hand sheets decreased with the addition of fi nes ( Figure 5). The effect of fi nes addition on roughness of  These results can be explained by the fact that fi nes act as a fi ller material in the paper structure. Positive effect of fi nes on surface smoothness was also reported by Waterhouse and Omiri (1993) and Lu (1999).

Air permeance 3.7. Propusnost zraka
In unbeaten pulps of all types of pulp, air permeance of hand sheets decreased dramatically with increasing addition of fi nes ( Figure 6). In Turkish Calabrian pines samples, the effect of fi nes on air permeance was more prominent than in other pulps. In Turkish Calabrian pine unbeaten kraft pulp, the addition of 5, 10, and 15 % fi nes caused an increase in air permeance of 9.24 %, 47.35 %, and 85.11 %, respectively (p<0.05). Air permeance of hand sheets of European aspen unbeaten kraft pulp and recycled unbeaten pulp decreased by 31.91 %, 67.54 %, 80.20 %, and  38.52 %, 67.57 %, 76.99 %, respectively (p<0.05), with the addition of 5, 10, and 15 % fi nes. Increasing the amount of fi nes in furnish also leads to decreased air permeance. Fines cause the decrease in air permeance by fi lling the voids of the fi ber network. In other words, air permeance ( Figure 6) tends to decrease with the addition of fi nes due to better conformity, reduction of spaces between fi bers and increase of resistance to air fl ow (Yasumura et al., 2012). Decreasing air permeance with the addition of fi nes can also be attributed to increasing apparent density with the addition of fi nes. At higher apparent densities, the pores in the sheet begin to close up due to better bonding. This led to the decrease in air permeance. Reduced air permeance retards moisture escape and slows the drying rate. Both factors contribute to decreased paper machine productivity (Seth, 2003). Lu (1999) reported that air permeance decreased with the addition of 20, 30, and 40 % fi nes to mechanical pulp from 2538 ml/min. to 922 ml/min., 124 ml/min., and 52 ml/min. respectively. Asikainen et al., (2010) noted that air resistance (Gurley method) increased with the addition of 10 % and 20 % primary fi nes to CTMP from 2.8 sec. to 7.7 sec. and 22.2 sec., respectively. On the other hand, Ferreira et al., (2000) noted that air permeance decreased when fi nes were removed from fi ber suspension from 54.5 ml/min. to 26 ml/min. Htun and de Ruvo (1978) reported that the removal of fi nes resulted in increased air permeability. The effect of fi nes on hand sheet air permeance has also been reported previously (Hartman, 1984 Regarding unbeaten pulp samples, air permeance of beaten pulps decreased with the addition of fi nes ( Figure 6). There was a linear correlation between fi nes addition ratio and air permeance of hand sheets. Air permeance of beaten kraft pulps of Turkish Calabrian pine and European aspen decreased by 50.79 %, 71.43 %, 86.51 %, and 37.08 %, 60.26 %, 78.80 %, respectively (p<0.05) with the addition of 5, 10, and 15 % fi nes. In the recycled beaten pulps, the addition of 5, 10, and 15 % fi nes caused an decrease in air permeance of 43.11 %, 59.89 %, and 85.33 %, respectively (p<0,05). For virgin pulps, the pulp freeness level had a more signifi cant effect on air permeance than the content of fi nes, and vice versa for recycled pulp. For example, when the 15 % fi nes were added to Turkish Calabrian pine kraft pulp, hand sheet air permeance decreased from 5756 ml/min. to 857 ml/min. However, hand sheet air permeance was decreased with beating up to 28 ºSR from 5756 ml/min. to 126 ml/min. On the other hand, in the recycled pulp, hand sheet air permeance was decreased with beating up to 28 ºSR from 4925 ml/min. to 2032 ml/min, while hand sheet air permeance was decreased from 4925 ml/min. to 1133 ml/ min with the addition of 15 % fi nes.

ZAKLJUČAK
Unless they are specifi cally removed, fi nes are present in any paper and infl uence its properties. In order to optimize the paper strength, it is important to control the fi nes content. In this study, the effect of fi nes on hand sheet properties was determined on dif-  ferent types of pulp (pine kraft pulp, aspen kraft pulp, and recycled pulp), as well as different pulp freeness levels (unbeaten pulp and 28 ºSR pulp). Based on the results, it can be concluded that secondary fi nes of recycled pulp have a signifi cant impact on hand sheet properties. The effect of fi nes on hand sheet properties correlates strongly with the type of pulp, freeness level of pulp, and amount of fi nes addition. The effect of the addition of fi nes on hand sheet properties of unbeaten pulps was more prominent than of beaten pulps. On the other hand, effect of fi nes on hand sheet properties of the unbeaten and beaten pulps was dependent on the type of pulp. In the unbeaten and beaten pulp samples, the effect of fi nes addition was more pronounced in European aspen kraft pulp and recycled pulp than in Turkish Calabrian pine kraft pulp. The differences in hand sheet properties became more visible with the increasing fi nes content. The highest paper strength increase rates were obtained from unbeaten pulps with 15 % fi nes. Paper strength of 15 % fi nes added unbeaten recycled pulp was higher than that of fi nes-free beaten recycled pulp. This demonstrates that it is possible to reduce the beating level by adding fi nes to recycled pulp. The results suggested that fi nes can be used as reinforcement for papermaking to improve the paper properties. In the papermaking process, fi nes can also be used as a potential control variable in order to obtain desirable paper properties. When the beating level and fi nes addition ratio are determined properly, refi ning energy requirements can be reduced, and paper strength can be improved.