Chem

    Cards (164)

    • Hygroscopicity and dimensional changes in wood
      • Due to the presence of water-loving molecules
      • Cellulose is mainly responsible
    • Cellulose
      • Responsible for strength in the wood because of its high degree of polymerization and linear orientation
    • Hemicellulose
      • Acts as a matrix for the cellulose and increases the packing density of the cell wall
      • Actual role in wood strength is unknown, but closely associated with lignin
    • Lignin
      • Holds fibers together
      • Holds cellulose molecules together within the fiber cell wall
    • Wood serves as source of food for a number of organisms
    • Resistance or susceptibility to biodeterioration
      • Depends on the presence of toxic chemicals in the extractive and lignin contents
    • Variation in the color in wood is due to the characteristics of some extractable compounds
    • Species showing no color difference simply indicate that no dark-colored extractives have formed
    • The presence of high amount of ash may result to excessive dulling of cutting materials
    • Wood is organic in nature, i.e. biological in origin
    • Elemental composition showed carbon to be the dominant element together with hydrogen, oxygen and a trace of inorganic compounds
    • Elemental composition of wood
      • Carbon (49%)
      • Oxygen (44%)
      • Hydrogen (6%)
      • Nitrogen (0.1%)
      • Ash (Ca, Mg, CO3, Si) (0.2-0.3%)
    • The elemental constituents of wood are combined into a number of organic polymers
    • Classification of cell wall components
      • Primary cell wall components (carbohydrate or non-carbohydrate)
      • Secondary components (not essential but influence physical and chemical behavior)
    • The chemical components of the cell wall are not uniformly distributed in the cell wall
    • Distribution of chemical components in cell wall
      • Highest concentration of lignin in the compound middle lamella, decreasing in the secondary cell wall layers
      • Less than 10% of the primary wall is cellulosic
      • Highest amount of cellulose (more than 50%) in the S2 layer of the secondary wall
      • Lignin content is inversely related to total carbohydrates
      • Cellulose and hemicellulose tend to vary more or less directly
    • Cross-linking between lignin and polysaccharide in plant cell-wall determines physical, chemical, and biological features of lignocellulosic biomass
    • The first direct proof of covalent bonding between plant cell-wall polysaccharides and lignin was first identified using nuclear magnetic resonance spectroscopy
    • Carbohydrates are the most abundant class of organic compounds, produced through the process of photosynthesis
    • Carbohydrates
      Carbon of hydrates, also known as saccharides or sugars
    • Classification of carbohydrates
      • Complexity (mono, di, oligo, & polysaccharides)
      • Sugar Units (homopolymer, heteropolymer)
      • Size (triose, tetrose, pentose, hexose)
      • C=O function (aldose or ketose)
      • Reactivity (reducing and non-reducing)
    • Monosaccharide
      The most basic form of carbohydrates, cannot be broken down into smaller carbohydrate unit
    • Monosaccharides
      • Glucose
      • Fructose
      • Galactose
    • Disaccharide
      Sugar formed when two monosaccharides are joined by glycosidic linkage through condensation or dehydration synthesis
    • Disaccharides
      • Sucrose (glucose and fructose)
      • Maltose (2 glucose units)
      • Lactose (galactose and glucose)
    • Oligosaccharide
      Contains three to ten monosaccharide units
    • Oligosaccharides
      • Raffinose (galactose, glucose, fructose)
      • Stachyose (2 galactose, 1 glucose, 1 fructose)
    • Polysaccharide
      Composed of glucose sugar units, e.g. starch and cellulose
    • Cellulose and starch are identical in every aspect except the arrangement of bonds
    • Comparison of cellulose and starch
      • Cellulose: glucose units linked via β 1-4 glycosidic bonds
      • Starch: glucose units linked via α 1-4 and α 1-6 glycosidic bonds
    • Humans cannot digest cellulose as the enzymes cannot hydrolyze β linkages, but ruminants can utilize cellulose due to cellulase-producing microorganisms
    • Homopolymer
      Composed of just one type of sugar unit
    • Heteropolymer
      Composed of at least two types of sugar units
    • Cellulose is an example of a homopolymer, hemicellulose is an example of a heteropolymer
    • Aldehyde
      Functional group with a carbonyl (C=O) group at the end of a carbon chain
    • Ketone
      Functional group with a carbonyl (C=O) group in the middle of a carbon chain
    • Classification of carbohydrates by number of carbon atoms
      • Triose (3 carbons)
      • Tetrose (4 carbons)
      • Pentose (5 carbons)
      • Hexose (6 carbons)
    • Reducing sugar
      Has a hemiacetal group that can be oxidized, reacts with Tollen's, Benedict's or Fehling's reagents
    • Non-reducing sugar
      Does not have a hemiacetal group, cannot be oxidized, does not react with Tollen's, Benedict's or Fehling's reagents
    • Tollen's reagent test differentiates aldehydes and ketones, produces a silver mirror with aldehydes
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