Evaluation of Rhododendron Luteum and Rhododendron Ponticum in Pulp and Paper Production

• In this study, Rhododendron luteum and Rhododendron ponticum were evaluated as raw material for pulp and paper production. 12 different sodium borohydride (NaBH 4 ) added cooking trials were performed for each sample and kraft method was used for pulp production. Pulp properties, such as yield, kappa number and viscosity, and physical properties, such as breaking length and burst index, were determined for each trial. Besides, the effects of active alkali and NaBH 4 on the pulp and paper properties were also examined. Optimum cooking conditions were obtained by using 18 % active alkali for NaBH 4 -free cooking experiments and 0.5 % NaBH4 and 18 % active alkali for NaBH4-added cooking experiments. In NaBH 4 -added pulping condition, the screened yield, kappa number and viscosity of R. luteum were found to be 43.4 %, 40.1 and 949 cm 3 /g 1 , respectively. The respec-tive values for R. ponticum were 41.9 %, 44.5 and 885 cm 3 /g 1 . The screened yields of R. luteum and R. ponticum increased by about 2.8 % and 5.3 %, respectively, with 5 % addition of NaBH 4 compared to NaBH 4 -free cooking experiments. Furthermore, with the addition of NaBH 4 , the kappa numbers decreased while the viscosity increased. The physical properties of the produced papers were also improved by using NaBH 4 in cooking liquor. According to the obtained results, it was found that R. luteum and R. ponticum species can be evaluated for pulp and paper production.


UVOD
In the second half of the twentieth century, especially with the increase of world population and the increase in demand for forest products due to rapid developments in technology, the decrease in forest areas led the forest products industry to search for raw materials as an alternative to wood (Oner and Aslan, 2002;Tutus et al., 2011). Non-wood and new wood products are one of the best alternative raw materials (Kaldor, 1992;Comlekcioglu et al., 2016). Due to the rapid increase in paper consumption in recent years, alternative fi brous materials have gained importance in the pulp and paper industry (Daud and Law, 2011). The search for new wood raw materials still continues in the world.
Rhododendron species, a valuable ornamental shrub, have been cultivated since the 18 th century. These species belong to the heath or Ericaceae family. Rhododendron, with about 1000 different species, extends from Southwest Asia to New Guinea. Some Rhododendron species are large species with a tree-type growth habit. It is evergreen or rarely deciduous. Turkish rhododendrons grow naturally up to 3000 m above the sea level. One of the most remarkable Rhododendron species in moist forest formations covering the northern coast of Turkey is R. luteum and the most common Rhododendron is R. ponticum. Fiber length, fi ber width, lumen diameter and cell wall thicknesses of R luteum and R. ponticum are approximately 0.9-1.0 mm, 17-19 μm, 7-9 μm and 3-4 μm, respectively. Besides, these species have high holocellulose (77-80 %) and alpha cellulose (47-48 %) contents, which are important carbohydrates for pulp and paper industry (Birinci, 2008;Camlibel, 2008).
Although they appear on the northern slopes of the mountains on the Black Sea coast, there are more species in the Eastern Black Sea Region (Avci, 2004). In many studies, Rhododendron species have generally been evaluated for the production of medium density fi berboard (MDF) (Akgul et al., 2012;Akgul and Camlibel, 2008;Ayrilmis et al., 2014). Besides, some studies have determined the chemical composition of some Rhododendron species (Birinci, 2008;Shrestha and Budhathoki, 2012).
The kraft method is the most commonly used method for obtaining pulp suitable for papermaking. Increasing the pulp yield in pulp production is very important for the pulp and paper industry in terms of cost and economy. Modifying the kraft cooking process, e.g. by adding NaBH 4 , is a way of increasing the pulp yield (Courchene, 1998 There is little information about the use of Rhododendron species in wood-based industries and there is no study on their use in pulp and paper production. The aim of this study was to evaluate Rhododendron luteum and Rhododendron ponticum stalks for pulp and paper production, using Kraft-NaBH 4 cooking methods.

MATERIJALI I METODE
R. luteum and R. ponticum species were obtained from Akdamar Village of Akçaabat district of Trabzon province in Turkey. The chemical compositions of R. luteum and R. ponticum were determined in a previous study (Birinci, 2008) and are presented in Table 1 with some wood and non-wood species.
According to Table 1, the chemical composition of Rhododendron species is similar to that of hardwoods species. Rhododendron species show similarities among themselves. However, the lignin content of R. ponticum was higher than that of R. luteum. Due to their high holocellulose contents, it was concluded that Rhododendron species were considered suitable for pulp and paper production.
The samples were chipped and air dried. 12 cooking trials were applied on each species, using Kraft-NaBH 4 method given in Table 2 in order to determine optimum pulping conditions.
Cooking trials of the species were applied in a rotary digester with a 15-liter capacity and high pressure resistant. After cooking processes, the pulps were washed with tap water until the black liquor was removed, and the washed pulps were transferred to 0.15 mm slotted screen. Screened pulp and screen reject yields were calculated after the screening process. The kappa numbers and viscosity of the screened pulps were determined according to TAPPI T 236 om-13 and TAPPI T 230 om-08, respectively (Anonymous, 1998).
The pulps were beaten to 25 ±3 o SR (Schopper Riegler) freeness level in the hollander beater according to TAPPI T 200 sp-96. Ten test papers were produced from the pulps obtained from each cooking trial. The breaking lengths and burst indices of the papers .........Birinci, Tutuş, Çiçekler: Evaluation of Rhododendron Luteum and Rhododendron...
were determined according to TAPPI T 494 om-01 and TAPPI T 403 om-91, respectively (Anonymous, 1998). In order to determine the effects of active alkali and NaBH 4 , the optimum cooking parameters were used.

REZULTATI I RASPRAVA
The yield and chemical properties of R. luteum and R. ponticum pulps used in this study are presented in Table 3.
The screened yield and viscosity of R. ponticum was found lower than that of R. luteum by about 5.6 % and 15.5 %, respectively. The kappa numbers of R. ponticum and R. luteum were determined as 49.24 and 45.74. According to these results, R. luteum is more suitable for pulping production than R. ponticum. The effects of NaBH 4 on the properties of Rhododendron pulp are shown in Figure 1.
With the addition of NaBH 4 to the cooking liquor, the yield and viscosity of the pulps increased and kappa numbers decreased. NaBH 4 was effective on the screened yields as it had the ability to stop peeling reactions occurring in cellulose chains (Istek and Ozkan, 2008;Tutus and Cicekler, 2016). NaBH 4 removes the lignin from the pulp i.e. selective lignin delignifi cation occurs, while increasing the viscosity by preserving   The breaking lengths and burst indices of R. luteum and R. ponticum papers used in this study are given in Table 4.
According to Table 4, the breaking lengths and burst indices of the R. ponticum papers were found to be higher than those of R. luteum. It is clearly seen that the physical properties of the papers improve with the increase of active alkali and NaBH 4 ratios ( Figure 2).
Many studies have reported that boron compounds prevent peeling reaction during cooking, resulting in less damage to carbohydrates and therefore improved physical and optical properties of the papers   Tables 3 and 4, optimum cooking conditions for the two species in NaBH 4added cooking experiments were determined by using 0.5 % NaBH 4 and 18 % active alkali (Cooking No: 7).

ZAKLJUČAK
In this study, pulp and papers of R. luteum and R. ponticum species were produced by using Kraft-NaBH 4 method and their properties were examined. As a result of this study, it was determined that the chemical properties of R. luteum and R. ponticum, such as yield, kappa and viscosity, were found to be better for pulp and paper industry. Besides, when the physical properties of the produced papers are examined, it is seen that they are suitable for the production of many paper types. The short-fi ber pulps obtained from R. luteum and R. ponticum can be mixed with long-fi ber pulps in certain proportions and evaluated for the production of many paper types. Since 70 % of short-fi ber raw materials are used for the production of writing-printing paper, the possibility of using R. luteum and R. ponticum species for the production of different types of quality paper is quite high. Breaking length / duljina lomljenja, km Burst indeks / indeks pucanja, kPa·m 2 ·g -1