Micro void system in pine cellulose

Cellulose, which originates in the plant cells as a porous material, subsequently may undergo different changes. Incrustations and phenomena connected with drying are the most important among these changes. It is impossible to predict what the physical state should be after the cellulose is further isolated and purified. Electron microscopy in the past has been surprisingly ineffective in unequivocally resolving the question of porosity of cellulosic materials. Indirect methods, such as the various density and absorption determinations, usually yield controversial results. In the present work, slash and loblolly pine pulp fibers were preswelled in different swelling media, sectioned, stained with phosphotungstic acid, and investigated with an electron microscope. Some regular patterns of voids became discernible along with numerous distortions and introduced artifacts. Essentially two types of enlarged micro pores were found: round holes and elongated fissures. Both features are believed to represent interstitial spaces among the different structural units of cellulose. The round openings could represent interstices among fibrils and fibrillar bundles. The fissures are openings between the individual lamellae. In the finished pulp some of the micro voids are apparently still filled, either partially or completely, with different foreign materials, such as hemi, lignin, and resin residues.