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60-441: In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote a change in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions , as well as other creative cross-linking methodologies. Although the term is used to refer to the "linking of polymer chains" for both sciences,

120-423: A permanent wave to hair involves the breaking and reformation of disulfide bonds. Typically a mercaptan such as ammonium thioglycolate is used for the breaking. Following this, the hair is curled and then "neutralized". The neutralizer is typically an acidic solution of hydrogen peroxide, which causes new disulfide bonds to form, thus permanently fixing the hair into its new configuration. Compromised collagen in

180-405: A smoke source to a wood fire. In cooking , lignin in the form of hardwood is an important source of these two compounds, which impart the characteristic aroma and taste to smoked foods such as barbecue . The main flavor compounds of smoked ham are guaiacol , and its 4-, 5-, and 6-methyl derivatives as well as 2,6-dimethylphenol. These compounds are produced by thermal breakdown of lignin in

240-426: A wound dressing since the U.S. Civil War . Cellulose acetate was first prepared in 1865. In years 1834-1844 the properties of rubber ( polyisoprene ) were found to be greatly improved by heating with sulfur , thus founding the vulcanization process. In 1884 Hilaire de Chardonnet started the first artificial fiber plant based on regenerated cellulose , or viscose rayon , as a substitute for silk , but it

300-545: A Nobel Prize for their discovery of catalysts for the polymerization of alkenes . Alan J. Heeger , Alan MacDiarmid , and Hideki Shirakawa were awarded the 2000 Nobel Prize in Chemistry for the development of polyacetylene and related conductive polymers. Polyacetylene itself did not find practical applications, but organic light-emitting diodes (OLEDs) emerged as one application of conducting polymers. Teaching and research programs in polymer chemistry were introduced in

360-423: A crucial part in conducting water and aqueous nutrients in plant stems. The polysaccharide components of plant cell walls are highly hydrophilic and thus permeable to water, whereas lignin is more hydrophobic . The crosslinking of polysaccharides by lignin is an obstacle for water absorption to the cell wall. Thus, lignin makes it possible for the plant's vascular tissue to conduct water efficiently. Lignin

420-507: A fibrous, tasteless material, insoluble in water and alcohol but soluble in weak alkaline solutions, and which can be precipitated from solution using acid. He named the substance "lignine", which is derived from the Latin word lignum , meaning wood. It is one of the most abundant organic polymers on Earth , exceeded only by cellulose and chitin . Lignin constitutes 30% of terrestrial non- fossil organic carbon on Earth, and 20 to 35% of

480-544: A lower redox potential than guaiacyl units. Because it is cross-linked with the other cell wall components, lignin minimizes the accessibility of cellulose and hemicellulose to microbial enzymes, leading to a reduced digestibility of biomass. Some ligninolytic enzymes include heme peroxidases such as lignin peroxidases , manganese peroxidases , versatile peroxidases , and dye-decolourizing peroxidases as well as copper-based laccases . Lignin peroxidases oxidize non-phenolic lignin, whereas manganese peroxidases only oxidize

540-675: A much wider range of properties than conventional cross-linked elastomers because the domains that act as cross-links are reversible, so can be reformed by heat. The stabilizing domains may be non-crystalline (as in styrene-butadiene block copolymers) or crystalline as in thermoplastic copolyesters. Alkyd enamels , the dominant type of commercial oil-based paint, cure by oxidative crosslinking after exposure to air. In contrast to chemical cross-links, physical cross-links are formed by weaker interactions. For example, sodium alginate gels upon exposure to calcium ions, which form ionic bonds that bridge between alginate chains. Polyvinyl alcohol gels upon

600-444: A renewable source of aromatic compounds for the chemical industry, with an addressable market of more than $ 130bn. Given that it is the most prevalent biopolymer after cellulose , lignin has been investigated as a feedstock for biofuel production and can become a crucial plant extract in the development of a new class of biofuels. Lignin biosynthesis begins in the cytosol with the synthesis of glycosylated monolignols from

660-471: A substance under vacuum and at high temperature) with tetramethylammonium hydroxide (TMAH) or cupric oxide has also been used to characterize lignins. The ratio of syringyl lignol (S) to vanillyl lignol (V) and cinnamyl lignol (C) to vanillyl lignol (V) is variable based on plant type and can therefore be used to trace plant sources in aquatic systems (woody vs. non-woody and angiosperm vs. gymnosperm). Ratios of carboxylic acid (Ad) to aldehyde (Al) forms of

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720-562: A wide range of other chemistry sub-disciplines like organic chemistry , analytical chemistry , and physical chemistry . Many materials have polymeric structures, from fully inorganic metals and ceramics to DNA and other biological molecules . However, polymer chemistry is typically related to synthetic and organic compositions . Synthetic polymers are ubiquitous in commercial materials and products in everyday use, such as plastics , and rubbers , and are major components of composite materials. Polymer chemistry can also be included in

780-523: Is 63.4% carbon, 5.9% hydrogen, 0.7% ash (mineral components), and 30% oxygen (by difference), corresponding approximately to the formula (C 31 H 34 O 11 ) n . Lignin is a collection of highly heterogeneous polymers derived from a handful of precursor lignols. Heterogeneity arises from the diversity and degree of crosslinking between these lignols. The lignols that crosslink are of three main types, all derived from phenylpropane: coniferyl alcohol (3-methoxy-4-hydroxyphenylpropane; its radical, G,

840-497: Is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls , especially in wood and bark , because they lend rigidity and do not rot easily. Chemically, lignins are polymers made by cross-linking phenolic precursors. Lignin was first mentioned in 1813 by the Swiss botanist A. P. de Candolle , who described it as

900-471: Is a highly crosslinked polymer that comprises the main structural material of higher plants. A hydrophobic material, it is derived from precursor monolignols . Heterogeneity arises from the diversity and degree of crosslinking between these lignols. Intrastrand DNA crosslinks have strong effects on organisms because these lesions interfere with transcription and replication . These effects can be put to good use (addressing cancer) or they can be lethal to

960-437: Is a radical-radical coupling, is catalysed by oxidative enzymes . Both peroxidase and laccase enzymes are present in the plant cell walls , and it is not known whether one or both of these groups participates in the polymerisation. Low molecular weight oxidants might also be involved. The oxidative enzyme catalyses the formation of monolignol radicals . These radicals are often said to undergo uncatalyzed coupling to form

1020-405: Is achieved through a more environmentally viable process than generic plastic manufacturing. Lignin removed by the kraft process is usually burned for its fuel value, providing energy to power the paper mill. Two commercial processes exist to remove lignin from black liquor for higher value uses: LignoBoost (Sweden) and LignoForce (Canada). Higher quality lignin presents the potential to become

1080-471: Is colored, it yellows in air, and its presence weakens the paper. Once separated from the cellulose, it is burned as fuel. Only a fraction is used in a wide range of low volume applications where the form but not the quality is important. Mechanical, or high-yield pulp , which is used to make newsprint , still contains most of the lignin originally present in the wood. This lignin is responsible for newsprint's yellowing with age. High quality paper requires

1140-547: Is commonly used to prepare antibody-hapten conjugates for antibody development. An in-vitro cross-linking method is PICUP ( photo-induced cross-linking of unmodified proteins ). Typical reagents are ammonium persulfate (APS), an electron acceptor, the photosensitizer tris-bipyridylruthenium (II) cation ( [Ru(bpy) 3 ] ). In in-vivo crosslinking of protein complexes, cells are grown with photoreactive diazirine analogs to leucine and methionine , which are incorporated into proteins. Upon exposure to ultraviolet light,

1200-463: Is derived from the coniferyl alcohol , which gives rise to G upon pyrolysis. In angiosperms some of the coniferyl alcohol is converted to S. Thus, lignin in angiosperms has both G and S components. Lignin's molecular masses exceed 10,000 u . It is hydrophobic as it is rich in aromatic subunits. The degree of polymerisation is difficult to measure, since the material is heterogeneous. Different types of lignin have been described depending on

1260-416: Is digested by " Alteromonas-like sub-group " bacteria symbionts in the typhlosole sub-organ of its cecum . Pyrolysis of lignin during the combustion of wood or charcoal production yields a range of products, of which the most characteristic ones are methoxy -substituted phenols . Of those, the most important are guaiacol and syringol and their derivatives. Their presence can be used to trace

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1320-498: Is measured. The more crosslinking, the less swelling is attainable. Based on the degree of swelling, the Flory Interaction Parameter (which relates the solvent interaction with the sample), and the density of the solvent, the theoretical degree of crosslinking can be calculated according to Flory's Network Theory. Two ASTM standards are commonly used to describe the degree of crosslinking in thermoplastics. In ASTM D2765,

1380-594: Is present in all vascular plants , but not in bryophytes , supporting the idea that the original function of lignin was restricted to water transport. It is covalently linked to hemicellulose and therefore cross-links different plant polysaccharides , conferring mechanical strength to the cell wall and by extension the plant as a whole. Its most commonly noted function is the support through strengthening of wood (mainly composed of xylem cells and lignified sclerenchyma fibres) in vascular plants. Finally, lignin also confers disease resistance by accumulating at

1440-462: Is sometimes called guaiacyl), sinapyl alcohol (3,5-dimethoxy-4-hydroxyphenylpropane; its radical, S, is sometimes called syringyl), and paracoumaryl alcohol (4-hydroxyphenylpropane; its radical, H, is sometimes called 4-hydroxyphenyl). The relative amounts of the precursor "monomers" (lignols or monolignols) vary according to the plant source. Lignins are typically classified according to their syringyl/guaiacyl (S/G) ratio. Lignin from gymnosperms

1500-780: Is treated with a crosslinking reagent . In vulcanization , sulfur is the cross-linking agent. Its introduction changes rubber to a more rigid, durable material associated with car and bike tires . This process is often called sulfur curing. In most cases, cross-linking is irreversible, and the resulting thermosetting material will degrade or burn if heated, without melting. Chemical covalent cross-links are stable mechanically and thermally. Therefore, cross-linked products like car tires cannot be recycled easily. A class of polymers known as thermoplastic elastomers rely on physical cross-links in their microstructure to achieve stability, and are widely used in non-tire applications, such as snowmobile tracks, and catheters for medical use. They offer

1560-416: The amino acid phenylalanine . These first reactions are shared with the phenylpropanoid pathway. The attached glucose renders them water-soluble and less toxic . Once transported through the cell membrane to the apoplast , the glucose is removed, and the polymerisation commences. Much about its anabolism is not understood even after more than a century of study. The polymerisation step, that

1620-606: The native state . Common crosslinkers include the imidoester crosslinker dimethyl suberimidate, the N-Hydroxysuccinimide -ester crosslinker BS3 and formaldehyde . Each of these crosslinkers induces nucleophilic attack of the amino group of lysine and subsequent covalent bonding via the crosslinker. The zero-length carbodiimide crosslinker EDC functions by converting carboxyls into amine-reactive isourea intermediates that bind to lysine residues or other available primary amines. SMCC or its water-soluble analog, Sulfo-SMCC,

1680-484: The wood used in the smokehouse. The conventional method for lignin quantitation in the pulp industry is the Klason lignin and acid-soluble lignin test, which is standardized procedures. The cellulose is digested thermally in the presence of acid. The residue is termed Klason lignin. Acid-soluble lignin (ASL) is quantified by the intensity of its Ultraviolet spectroscopy . The carbohydrate composition may be also analyzed from

1740-525: The 1940s. An Institute for Macromolecular Chemistry was founded in 1940 in Freiburg, Germany under the direction of Staudinger. In America, a Polymer Research Institute (PRI) was established in 1941 by Herman Mark at the Polytechnic Institute of Brooklyn (now Polytechnic Institute of NYU ). Polymers are high molecular mass compounds formed by polymerization of monomers . They are synthesized by

1800-562: The H 2 O 2 required for the function of lignin peroxidase and other heme peroxidases . Bacteria lack most of the enzymes employed by fungi to degrade lignin, and lignin derivatives (aliphatic acids, furans, and solubilized phenolics) inhibit the growth of bacteria. Yet, bacterial degradation can be quite extensive, especially in aquatic systems such as lakes, rivers, and streams, where inputs of terrestrial material (e.g. leaf litter ) can enter waterways. The ligninolytic activity of bacteria has not been studied extensively even though it

1860-498: The Klason liquors, although there may be sugar breakdown products (furfural and 5-hydroxymethylfurfural ). A solution of hydrochloric acid and phloroglucinol is used for the detection of lignin (Wiesner test). A brilliant red color develops, owing to the presence of coniferaldehyde groups in the lignin. Thioglycolysis is an analytical technique for lignin quantitation . Lignin structure can also be studied by computational simulation. Thermochemolysis (chemical break down of

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1920-418: The addition of borax through hydrogen bonding between boric acid and the polymer's alcohol groups. Other examples of materials which form physically cross-linked gels include gelatin , collagen , agarose , and agar agar . Crosslinking is often measured by swelling tests. The crosslinked sample is placed into a good solvent at a specific temperature, and either the change in mass or the change in volume

1980-489: The average length of the polymer, the progress of reactions, and in what ways the polymer branches. Polymers can be classified in many ways. Polymers, strictly speaking, comprise most solid matter: minerals (i.e. most of the Earth's crust) are largely polymers, metals are 3-d polymers, organisms, living and dead, are composed largely of polymers and water. Often polymers are classified according to their origin: Biopolymers are

2040-429: The broader fields of polymer science or even nanotechnology , both of which can be described as encompassing polymer physics and polymer engineering . The work of Henri Braconnot in 1777 and the work of Christian Schönbein in 1846 led to the discovery of nitrocellulose , which, when treated with camphor , produced celluloid . Dissolved in ether or acetone , it becomes collodion , which has been used as

2100-499: The chemical understanding of polymers and was followed by an expansion of the field of polymer chemistry during which such polymeric materials as neoprene, nylon and polyester were invented. Before Staudinger, polymers were thought to be clusters of small molecules ( colloids ), without definite molecular weights , held together by an unknown force . Staudinger received the Nobel Prize in Chemistry in 1953. Wallace Carothers invented

2160-547: The cornea, a condition known as keratoconus , can be treated with clinical crosslinking. In biological context crosslinking could play a role in atherosclerosis through advanced glycation end-products (AGEs), which have been implicated to induce crosslinking of collagen, which may lead to vascular stiffening. Proteins can also be cross-linked artificially using small-molecule crosslinkers. This approach has been used to elucidate protein–protein interactions . Crosslinkers bind only surface residues in relatively close proximity in

2220-911: The degree of branching , by its end-groups , crosslinks , crystallinity and thermal properties such as its glass transition temperature and melting temperature. Polymers in solution have special characteristics with respect to solubility , viscosity , and gelation . Illustrative of the quantitative aspects of polymer chemistry, particular attention is paid to the number-average and weight-average molecular weights M n {\displaystyle M_{n}} and M w {\displaystyle M_{w}} , respectively. The formation and properties of polymers have been rationalized by many theories including Scheutjens–Fleer theory , Flory–Huggins solution theory , Cossee–Arlman mechanism , Polymer field theory , Hoffman Nucleation Theory , Flory–Stockmayer theory , and many others. The study of polymer thermodynamics helps improve

2280-467: The diazirines are activated and bind to interacting proteins that are within a few ångströms of the photo-reactive amino acid analog (UV cross-linking). Polymer chemistry Polymer chemistry is a sub-discipline of chemistry that focuses on the structures of chemicals, chemical synthesis , and chemical and physical properties of polymers and macromolecules . The principles and methods used within polymer chemistry are also applicable through

2340-480: The dry mass of wood. Lignin is present in red algae , which suggest that the common ancestor of plants and red algae may have been pre-adapted to synthesize lignin. This finding also suggests that the original function of lignin may have been structural as it plays this role in the red alga Calliarthron , where it supports joints between calcified segments. The composition of lignin varies from species to species. An example of composition from an aspen sample

2400-413: The environment, lignin can be degraded either biotically via bacteria or abiotically via photochemical alteration, and oftentimes the latter assists in the former. In addition to the presence or absence of light, several of environmental factors affect the biodegradability of lignin, including bacterial community composition, mineral associations, and redox state. In shipworms , the lignin it ingests

2460-399: The extent of crosslinking and specificities of the crosslinking agents vary greatly. Crosslinking generally involves covalent bonds that join two polymer chains. The term curing refers to the crosslinking of thermosetting resins, such as unsaturated polyester and epoxy resin, and the term vulcanization is characteristically used for rubbers . When polymer chains are crosslinked,

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2520-426: The first synthetic rubber called neoprene in 1931, the first polyester , and went on to invent nylon , a true silk replacement, in 1935. Paul Flory was awarded the Nobel Prize in Chemistry in 1974 for his work on polymer random coil configurations in solution in the 1950s. Stephanie Kwolek developed an aramid , or aromatic nylon named Kevlar , patented in 1966. Karl Ziegler and Giulio Natta received

2580-494: The host organism. The drug cisplatin functions by formation of intrastrand crosslinks in DNA. Other crosslinking agents include mustard gas , mitomycin , and psoralen . In proteins , crosslinks are important in generating mechanically stable structures such as hair and wool , skin , and cartilage . Disulfide bonds are common crosslinks. Isopeptide bond formation is another type of protein crosslink. The process of applying

2640-435: The lignin polymer . An alternative theory invokes an unspecified biological control. In contrast to other bio-polymers (e.g. proteins, DNA, and even cellulose), lignin resists degradation. It is immune to both acid- and base-catalyzed hydrolysis. The degradability varies with species and plant tissue type. For example, syringyl (S) lignin is more susceptible to degradation by fungal decay as it has fewer aryl-aryl bonds and

2700-405: The lignin in lignocellulose , but others lack this ability. Most fungal lignin degradation involves secreted peroxidases . Many fungal laccases are also secreted, which facilitate degradation of phenolic lignin-derived compounds, although several intracellular fungal laccases have also been described. An important aspect of fungal lignin degradation is the activity of accessory enzymes to produce

2760-427: The lignols (Ad/Al) reveal diagenetic information, with higher ratios indicating a more highly degraded material. Increases in the (Ad/Al) value indicate an oxidative cleavage reaction has occurred on the alkyl lignin side chain which has been shown to be a step in the decay of wood by many white-rot and some soft rot fungi . Lignin and its models have been well examined by H and C NMR spectroscopy. Owing to

2820-520: The material becomes more rigid. The mechanical properties of a polymer depend strongly on the cross-link density. Low cross-link densities increase the viscosities of polymer melts . Intermediate cross-link densities transform gummy polymers into materials that have elastomeric properties and potentially high strengths. Very high cross-link densities can cause materials to become very rigid or glassy, such as phenol-formaldehyde materials. In one implementation, unpolymerized or partially polymerized resin

2880-437: The material properties of various polymer-based materials such as polystyrene (styrofoam) and polycarbonate . Common improvements include toughening , improving impact resistance , improving biodegradability , and altering a material's solubility . As polymers get longer and their molecular weight increases, their viscosity tend to increase. Thus, the measured viscosity of polymers can provide valuable information about

2940-444: The means of isolation. Many grasses have mostly G, while some palms have mainly S. All lignins contain small amounts of incomplete or modified monolignols, and other monomers are prominent in non-woody plants. Lignin fills the spaces in the cell wall between cellulose , hemicellulose , and pectin components, especially in vascular and support tissues: xylem tracheids , vessel elements and sclereid cells. Lignin plays

3000-586: The phenolic structures. Dye-decolorizing peroxidases, or DyPs, exhibit catalytic activity on a wide range of lignin model compounds, but their in vivo substrate is unknown. In general, laccases oxidize phenolic substrates but some fungal laccases have been shown to oxidize non-phenolic substrates in the presence of synthetic redox mediators. Well-studied ligninolytic enzymes are found in Phanerochaete chrysosporium and other white rot fungi . Some white rot fungi, such as Ceriporiopsis subvermispora , can degrade

3060-434: The polymerization process and can be modified by the additive of monomers. The additives of monomers change polymers mechanical property, processability, durability and so on. The simple reactive molecule from which the repeating structural units of a polymer are derived is called a monomer. A polymer can be described in many ways: its degree of polymerisation , molar mass distribution , tacticity , copolymer distribution,

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3120-434: The removal of lignin from the pulp. These delignification processes are core technologies of the papermaking industry as well as the source of significant environmental concerns. In sulfite pulping , lignin is removed from wood pulp as lignosulfonates , for which many applications have been proposed. They are used as dispersants , humectants , emulsion stabilizers , and sequestrants ( water treatment ). Lignosulfonate

3180-415: The sample is weighed, then placed in a solvent for 24 hours, weighed again while swollen, then dried and weighed a final time. The degree of swelling and the soluble portion can be calculated. In another ASTM standard, F2214, the sample is placed in an instrument that measures the height change in the sample, allowing the user to measure the volume change. The crosslink density can then be calculated. Lignin

3240-410: The site of pathogen infiltration, making the plant cell less accessible to cell wall degradation. Global commercial production of lignin is a consequence of papermaking. In 1988, more than 220 million tons of paper were produced worldwide. Much of this paper was delignified; lignin comprises about 1/3 of the mass of lignocellulose, the precursor to paper. Lignin is an impediment to papermaking as it

3300-439: The strong views espoused by Emil Fischer , his direct supervisor, denying the possibility of any covalent molecule exceeding 6,000 daltons. Cellophane was invented in 1908 by Jocques Brandenberger who treated sheets of viscose rayon with acid . The chemist Hermann Staudinger first proposed that polymers consisted of long chains of atoms held together by covalent bonds , which he called macromolecules . His work expanded

3360-444: The structural and functional materials that comprise most of the organic matter in organisms. One major class of biopolymers are proteins , which are derived from amino acids . Polysaccharides , such as cellulose , chitin , and starch , are biopolymers derived from sugars. The poly nucleic acids DNA and RNA are derived from phosphorylated sugars with pendant nucleotides that carry genetic information. Synthetic polymers are

3420-664: The structural materials manifested in plastics , synthetic fibers , paints , building materials , furniture , mechanical parts, and adhesives . Synthetic polymers may be divided into thermoplastic polymers and thermoset plastics . Thermoplastic polymers include polyethylene , teflon , polystyrene , polypropylene , polyester , polyurethane , Poly(methyl methacrylate) , polyvinyl chloride , nylons , and rayon . Thermoset plastics include vulcanized rubber , bakelite , Kevlar , and polyepoxide . Almost all synthetic polymers are derived from petrochemicals . Lignin Lignin

3480-601: Was also the first family of water reducers or superplasticizers to be added in the 1930s as admixture to fresh concrete in order to decrease the water-to-cement ( w/c ) ratio, the main parameter controlling the concrete porosity , and thus its mechanical strength , its diffusivity and its hydraulic conductivity , all parameters essential for its durability. It has application in environmentally sustainable dust suppression agent for roads. Also, lignin can be used in making biodegradable plastic along with cellulose as an alternative to hydrocarbon-made plastics if lignin extraction

3540-417: Was first described in 1930. Many bacterial DyPs have been characterized. Bacteria do not express any of the plant-type peroxidases (lignin peroxidase, Mn peroxidase, or versatile peroxidases), but three of the four classes of DyP are only found in bacteria. In contrast to fungi, most bacterial enzymes involved in lignin degradation are intracellular, including two classes of DyP and most bacterial laccases. In

3600-428: Was very flammable. In 1907 Leo Baekeland invented the first polymer made independent of the products of organisms , a thermosetting phenol - formaldehyde resin called Bakelite . Around the same time, Hermann Leuchs reported the synthesis of amino acid N-carboxyanhydrides and their high molecular weight products upon reaction with nucleophiles, but stopped short of referring to these as polymers, possibly due to

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