**1.2 Recycling influence on pulp fibre quality**

Raw material source for paper production including usage of secondary fibres as well as ways of its obtaining varies continually. This fact represents basic and more and more difficult issue in paper production research.

Paper is nonhomogeneous network of pulp fibres. Except of fibres real papers contain also fillers, sizing agents, colours and other auxiliary materials. Paper properties are defined by properties of all used materials and technology of paper process. Describing this wide complex of variables is actually unreal. It is possible to partially describe the properties of laboratory testing sheets prepared under standard conditions or eventually of orthotropic paper made from pulp fibres on paper machine.

Description of fibres properties is based on the dimension characteristic and derived numeric parameters. This description is insufficient and only approximative. Dimensional analysis does not express fibres status and vanish the fine portion which influence significantly paper properties (Blažej and Krkoška, 1989).

Pulp fibres dimensions and physic-chemical properties are modified significantly by process of defibering, beating and refining, i.e. via mechanical effect of pulper and beating apparatus in aqueous medium. The interaction between pulp fibres and water is crucial at mentioned operations. The result reached by beating is influenced by fibres parameters (theirs origin, preparation method, drying method and deepness), mill parameters and beating process parameters (e.g. swelling level) (Hnětkovský, 1983a).

The characteristic differences of paper made by secondary fibres and freshly prepared fibres are similar to deviations between properties of paper made by fibres in wet and dry stage. Basic properties of fresh wet fibres change within drying process. Defibering and beating represent regeneration process. However this process is not complete, moreover it introduces additional destructive changes. Similar effect is observed during old paper defibering. Several fibres properties are changed irreversibly. Changes relevancy depends on the cycle count of fibres utilization (regeneration and usage for new paper production) and the way of paper products utilization (ageing destruction). The parameters used for the description of primary fibres paper properties are also suitable for the description of paper properties made by secondary fibres and fibre ageing changes (Blažej and Krkoška, 1989).

The fibres wear irreversibly and change theirs properties within the count of utilization cycles. Defibering and beating induce water absorption, swelling and partial regeneration of original properties. Repeated beating and drying during several production cycles provoke gradual decrease of swelling ability, which determine fibres bonding ability. Moreover a

Whereas the majority of mixed grades and OCC grades of recovered paper primarily find use in the production of packaging papers and board (84 %), almost all deinking grades

Waste paper participates in total paper production (60 %) mostly in Nederland and Great Britain. This limit is almost reached in Germany. Whereas Nordic countries that have sufficient wood raw material source are using only 10 – 15 % of waste paper as a secondary

Raw material source for paper production including usage of secondary fibres as well as ways of its obtaining varies continually. This fact represents basic and more and more

Paper is nonhomogeneous network of pulp fibres. Except of fibres real papers contain also fillers, sizing agents, colours and other auxiliary materials. Paper properties are defined by properties of all used materials and technology of paper process. Describing this wide complex of variables is actually unreal. It is possible to partially describe the properties of laboratory testing sheets prepared under standard conditions or eventually of orthotropic

Description of fibres properties is based on the dimension characteristic and derived numeric parameters. This description is insufficient and only approximative. Dimensional analysis does not express fibres status and vanish the fine portion which influence

Pulp fibres dimensions and physic-chemical properties are modified significantly by process of defibering, beating and refining, i.e. via mechanical effect of pulper and beating apparatus in aqueous medium. The interaction between pulp fibres and water is crucial at mentioned operations. The result reached by beating is influenced by fibres parameters (theirs origin, preparation method, drying method and deepness), mill parameters and

The characteristic differences of paper made by secondary fibres and freshly prepared fibres are similar to deviations between properties of paper made by fibres in wet and dry stage. Basic properties of fresh wet fibres change within drying process. Defibering and beating represent regeneration process. However this process is not complete, moreover it introduces additional destructive changes. Similar effect is observed during old paper defibering. Several fibres properties are changed irreversibly. Changes relevancy depends on the cycle count of fibres utilization (regeneration and usage for new paper production) and the way of paper products utilization (ageing destruction). The parameters used for the description of primary fibres paper properties are also suitable for the description of paper properties made by secondary fibres and fibre ageing changes (Blažej and Krkoška, 1989).

The fibres wear irreversibly and change theirs properties within the count of utilization cycles. Defibering and beating induce water absorption, swelling and partial regeneration of original properties. Repeated beating and drying during several production cycles provoke gradual decrease of swelling ability, which determine fibres bonding ability. Moreover a

(88 %) go to graphic paper production (Putz, 2000).

**1.2 Recycling influence on pulp fibre quality** 

difficult issue in paper production research.

paper made from pulp fibres on paper machine.

significantly paper properties (Blažej and Krkoška, 1989).

beating process parameters (e.g. swelling level) (Hnětkovský, 1983a).

fibres (Milichovský, 1994).

fibre shortening is observed within increasing count of utilization cycles. Mentioned modifications reflect in paper properties (Blažej and Krkoška, 1989).

Experiences gained during old paper utilization prove that these fibres show significantly different properties comparing to freshly prepared fibres (Blechschmidt, 1979; Nordman, 1976; Laivins and Scallan, 1993; Hubbe et al., 2007; Howard, 1990, 1994, 1995; Nazhad and Paszner, 1994; Phipps, 1994; Ackermann et al., 2000; Shao and Hu, 2002; Hubbe and Zhang, 2005; Nazhad, 2005). Fibre re-utilization creates extremely non-homogenous mixture of variously old fibres. Old paper is composed by all types of manufactured paper and board. Additional inhomogenity is caused by the presence of fibres used for several times but unequally (Attwood, 1983).

Pulp fibres are modified within the paper production by beating. Whereas the beating condition optimization is very important because of created fibrillation of fibre surface, release of fine portion and cell wall delamination. Paper rigidity increases during the beating. However recycled fibres repeated beating and drying lead to the decrease of interfibre bonding potential (Stürmer and Göttsching, 1979; Peng et al.,1994).

Göttsching (1976) detected by strength measuring at zero-span of jacks that recycled fires resistance does not change practically. Decrease of paper resistance made by recycled fibres could be explained as the consequence of inter-fibre bond strength decrease.

Decrease of bonding ability and strength of recycled fibres bring the improvement of several utility characteristics as increased velocity of dewatering and drying, air permeability, blotting paper ability, improvement of light diffusion, opacity, and dimensional stability of paper (Göttsching and Stürmer, 1975), which is linked with decreased fibres ability of swelling in contact with water (Ackermann et al., 2000).

Fibres swelling in width orientation and increase of wet fibre flexibility prove inner fibrilation caused by beating. Beating process creates submicroscopic areas in lamellar structure of kraft pulp fibre cell wall. Mentioned areas have tendency to close themselves semi-reversibly during drying (Jayme and Büttel ,1968; Paavilainen, 1993).
