papr5 - Raw Materials for Papermaking Lecture 5 PAPR 1000...

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Unformatted text preview: Raw Materials for Papermaking Lecture 5 PAPR 1000 Introduction to Pulp and Paper Manufacturer 1 Raw Material for Papermaking The most common raw material is wood trees softwood hardwood Other non-wood fiber materials are cotton, hemp, bamboo, corn husks, straws, and grasses etc. seasonality of annual crops which requires considerations of storing, cleaning, handling, and shipping 2 Raw Material for Papermaking This is where it starts. 3 Crown The crown consists of the leaves and branches at the top of a tree. The leaves are the food factories of a tree. They contain chlorophyll, which facilitates photosynthesis and gives leaves their green color. 4 Photosynthesis 6 H2O + 6CO2 ----> C6H12O6 + 6O2 5 Chorophyll 6 Trunk Supports the crown Consists of four layers of tissue Amazing system of pipelines (roots and leaves) Tubes carry water and minerals up from the roots to the leaves, and they carry sugar down from the leaves to the branches, trunk and roots. 7 Heartwood As a tree grows, older xylem cells in the center of the tree become inactive and die, forming heartwood. Because it is filled with stored sugar, dyes and oils, the heartwood is usually darker than the sapwood. The main function of the heartwood is to support the tree. 8 Xylem or Sapwood The xylem, or sapwood, comprises the youngest layers of wood. Its network of thickwalled cells brings water and nutrients up from the roots through tubes inside of the trunk to the leaves and other parts of the tree. As the tree grows, xylem cells in the central portion of the tree become inactive and die. These dead xylem cells form the tree's heartwood. 9 Cambium The cambium is a very thin layer of growing tissue that produces new cells that become either xylem, phloem or more cambium. Every growing season, a tree's cambium adds a new layer of xylem to its trunk, producing a visible growth ring in most trees. The cambium is what makes the trunk, branches and roots grow larger in diameter. 10 Bark The trunk, branches and twigs of the tree are covered with bark. The outer bark, which originates from phloem cells that have worn out, died and been shed outward, acts as a suit of armor against the world by protecting the tree from insects, disease, storms and extreme temperatures. In certain species, the outer bark also protects the tree from fire. 11 Phloem/Inner Bark The phloem or inner bark, which is found between the cambium and the outer bark, acts as a food supply line by carrying sap (sugar and nutrients dissolved in water) from the leaves to every living cell in the tree. 12 Roots A tree's roots absorb water and nutrients from the soil, store sugar and anchor the tree upright in the ground. The majority of the root system is located in the upper 12 to 18 inches of soil because the oxygen that the roots require to function properly is most abundant there. 13 Overview 14 The function and characteristics of various tree stem tissues Tissue Outer bark Phloem and Xylem Cambium Growth ring Earlywood Latewood Sapwood Heartwood Juvenile wood Function Physical and biological protection Conduction of food up and down the stem Thin layer of cells giving rise to all the wood and inner bark fibers. The tree stem grows outward One year's growth of wood Low density wood designed for conduction of water High density wood for strength to support the tree Conduction of sap (water, soil nutrients) up to the leaves Provides strength to support the crown The first 10 growth rings surrounding the pith. Usually 15 low density and relatively short fibers. Pulping Variables Moisture content Specific gravity Tension and compressive strength properties Chemical composition- cellulose, hemicellulose, lignin, and extractives Length of storage- amount of decay and extractives content Chip dimensions Wood species 16 Wood Classification Botanically, woods are classified into two major groups The gymnosperms are commonly called softwoods or conifers The angiosperms are the hardwoods or deciduous 17 Softwoods Wood, or trees from the Gymnosperms, a subdivision of the division Spermatophytes (plants with seeds) are known as softwoods. Gymnosperms are also called conifers. These trees retain their needles (leaves) in winter. Softwoods are characterized by relatively simple wood anatomy consisting of 90-95% longitudinal fiber tracheids 2.5-7 mm long and 25-60 micron wide, 5-10% ray cells, and 0.5-1.0% resin cells. 18 Hardwoods Wood, or trees from the Angiosperms, a subdivision of the division Spermatophytes are known as hardwoods. Angiosperms are also called broadleafs or deciduous. These trees loose their leaves in winter. Hardwoods have complex structures including vessel elements, fiber tracheids, libriform fibers, ray cells, and parenchyma cells. 19 Hardwood and Softwood Deciduous Usually bear broad leaves that are shed each autumn seeds are contained in a fruit wood is generally harder than wood from evergreens Conifer Leaves (needles) remain on the tree for two or more seasons seeds are contained in a cone wood is soft and resinous Conifers used are mainly spruce, fir and pine, whereas beech, birch, poplar and eucalyptus are the most important deciduous varieties used for paper. 20 Job of the Paper Engineer Determine the best way to remove the desired chemical components from the wood (cellulose, hemicellulose, lignin and resins) Understand wood chemistry Understand chemical reactions Understand engineering economics Understand unit of operations 21 22 Wood Fibers Softwood & Hardwood 23 Layers of Softwood Tracheid The cell wall is composed of a great number of microfibrils, as indicated by the fine lines in this diagram. A microfibril is a bundle of cellulose polymer chains. Orientation of microfibrils is very specific for each layer. As shown here, microfibrils of the S2 layer run more or less parallel to the long axis of the cell, 24 Layers of Softwood Tracheid whereas microfibrils of the S1 and S3 run more or less horizontally. Orientation of microfibrils in the primary wall is random. Minute structure of the cell wall largely determines properties of individual fibers as well as wood as a whole. 25 Microfibril Angle 26 Cellulose Polymer of anhydroglucopyranose Linear unbranched long chain polymer Degree of polymerization (DP): 3,00010,000 Partially crystalline structure Cellulose fiber provides structural integrity to tree 27 28 3-D Image of Cellulose 29 Hemicellulose Composed of combination of 5 and 6 carbon ring sugars Two main types: xylan and glucomannan Possesses side groups Amorphous DP range from 50 to 300 Supportive matrix for the cellulose microfibrils 30 31 Lignin Lignin is a class of complex, high molecular weight polymers whose exact structure varies It is an amorphous, i.e., not crystalline, polymer that acts as a binding agent to hold cells together Co-polymer of phenylpropanes Interunit linkages involve both ether and C-C bonds Molecular weight unknown, but very high Cross-linked net work polymer 32 Lignin 33 Extractives Large variety of low MW compounds Hydrophobic substance soluble in neutral, non-polar organic solvents. Include Phenols, glycosides, fatty acids, resin-acids, terpenes, tanins, etc. 34 Cellulose Fiber Characteristics The cellulose fibers used in making paper have certain inherent properties which enable them to form a web or sheet of paper hydrophilicity, which permits them to be readily dispersed in water a fine structure which permits fibrillation sufficient fiber length to form a highly entangled sheet of considerable strength the ability to form hydrogen bonds between fibers as the web dries, thus providing additional strength in the sheet of paper 35 Hydrogen Bond A hydrogen bond is a type of attractive intermolecular force that exists between two partial electric charges of opposite polarity. 36 ...
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