There are many alternatives available to replace all the plastic that is used. Your email address will not be published. Your wishlist is empty. View Wishlist. Cart Cart 0. Order before 11am for Same Day Dispatch! Ph or Live Chat pm Mon — Fri. Shipping Calculated at Checkout. What is the most difficult material to recycle? Share 0 0 0. Comments 0. Leave a reply Click here to cancel the reply Your email address will not be published. Thus lignin is not a polysaccharide, but a complex substance consisting of aromatic structures with alkoxy and hydrocarbon substituents that link the basic aromatic unit into a macromolecular structure through carbon-carbon and carbon-oxygen bonds.
It is not heterogeneous both in chemical composition and molar mass. Lignocellulose is strong and tough, and provides physical, chemical and biological protection to the plant. Lignin is resistant to peroxidation see oxo-biodegradable polymers , as a result of the presence of many antioxidant-active phenolic groups, which act as protective agents against abiotic peroxidation and biological attack by peroxidase enzymes [ 43 - 45 ]. It is also present in some algae.
After the cellulose, it is the second most abundant organic polymer on earth, with about 50 million tons being industrially produced annually. It is the main humus-forming component, which provides nutrients and electric charges to the soils. Humus is slowly biodegradable by oxidase and peroxidase enzymes, produced especially by fungi.
Although basidiomycetous white-rot fungi and related litter-decomposing fungi are the most efficient degraders of lignin, mixed cultures of fungi, actinomycetes, and bacteria in soil and compost can also mineralize lignin [ 46 ].
The main industrial use of lignin is still the power generation, as biofuel. A biodegradable material based on lignin, obtained as a byproduct from the manufacture of paper, mixed with vegetable fibers, is manufactured by Tecnaro under the trade name of Arboform [ 47 ]. Its mechanical properties show high rigidity and low deformability. The amide linkages are readily degraded by enzymes, particularly proteases. Soy proteins have been used for edible films and even automotive parts, but proteins have not been consolidated as a thermoplastic of worldwide use [ 48 ].
Polyamino acids with free carboxylic groups, such as polyaspartic acid and polyglutamic acid, are excellent candidates for use as water soluble biodegradable polymers [ 40 ]. In addition to thermoplastics, other possible applications of proteins are in coatings, adhesives, surfactants and gelatin capsules for pharmaceutical uses. Natural rubber is poly 1,4-cis-isoprene , naturally synthesized by the rubber tree, Hevea brasiliensis , present in its milky sap or latex.
It is also synthesized industrially by polyaddition of isoprene. It partially crystallizes when stretched. Due to the long sequences of double bonds one per monomeric unit , this rubber has a high reactivity with oxygen, undergoing the peroxidation reactions, yellowing very quickly, and being biodegraded at a relatively high rate [ 1 ]. The hydrogen atoms attached to carbon atoms at the alpha position relative to the unsaturations are more reactive, or more labile [ 21 ].
Among the main applications are tires and tubes. Polyvinyl alcohol is a biodegradable polymer obtained by partial or complete hydrolysis of polyvinyl acetate PVA, of petrochemical origin to remove acetate groups Figure 2. The vinyl alcohol monomer almost exclusively exists as the tautomeric form acetaldehyde, which does not polymerize [ 49 ].
PVOH is the only water soluble biodegradable polymer, whose main chain consists only of carbon atoms. Solubility and biodegradability are imparted by the hydroxyl groups, that are capable of establishing hydrogen bonds with water. The partial hydrolysis leaves acetate residues, that allow PVOH solubility in cold water, and decrease the biodegradability. Even being an atactic polymer, with non-organized space distribution of the hydroxyl groups in the main chain, PVOH shows crystallinity, because the hydroxyl groups are small enough to accommodate within the crystal, not hindering it [ 49 ].
Annual production exceeds 1 million tons. Some major applications are: thickener in paint industry; paper coating, hair sprays; shampoos; adhesives; biodegradable products for the feminine hygiene; diapers bottoms; water soluble packaging films detergents, disinfectants, scouring powder, pesticides, fertilizer, laundry, etc. It is believed that the PVOH degrading microorganisms are not spread throughout the environment, and that they are predominantly bacteria and fungi yeasts and moulds [ 50 ].
Before the start of biodegradation, a period of acclimatization may be required. Acclimatization natural conditions and acclimation laboratory conditions are the adjustment process of an organism or a colony to an environmental change, normally occurring in short periods of time days or weeks.
The biodegradation mechanism consists of a random cleavage of 1,3-diketones, that are formed by the enzymatic oxidation of the secondary hydroxyls [ 51 ]. EVOH is a copolymer of ethylene and vinyl alcohol, obtained from ethylene and vinyl acetate, followed by hydrolysis. It is used as an oxygen barrier film in multilayer films for packaging. Its high cost limits its applications as a biodegradable material. The second group of biodegradable polymers is formed by hydro-biodegradable materials, i.
Therefore, the decomposition process of the polymer occurs in two stages: first, the molecules break up into small fragments by hydrolysis; and second, these fragments are biodegraded by microorganisms. In both stages, the presence of water is essential, both to chemically fragment the molecules, and to be consumed by microorganisms, that need much water in their cells. To this group belong the aliphatic i.
PCL can also be biodegraded directly by enzymes produced by microorganisms, without the initial stage of hydrolysis [ 24 ].
Polyesters are polymers in which the bonds between the monomers occur via ester groups. There are many types of natural esters, and their degrading enzymes - the esterases - are present everywhere, together with the living organisms. The ester bonds are generally easy to hydrolyze [ 20 ]. The group of biodegradable polyesters mainly consists of: a linear aliphatic i.
Polyhydroxyalkanoates PHAs are polyesters of several hydroxyalkanoates that are synthesized by many microorganisms as a carbon and energy storage material. The hydroxyalkanoates can be synthesized from natural substances such as sucrose e. Precisely for this reason, this material is rapidly biodegraded in various environmental conditions by many different organisms.
The molecular weight generally varies from 50, to 2,, g mol The monomers are all optical isomers R, the only ones capable of being hydrolyzed by depolymerases, in the isotactic form [ 53 ]. PHAs polymers and copolymers are semicrystalline, with the molecules conformed in helices in the crystalline lamellae, which form spherulites.
The native intracellular granules of PHAs with 0. PHAs are attacked by intracellular PHAs- depolymerases enzymes, but not extracellular depolymerases [ 54 , 55 ]. PHB is a biological storage material that is used by archaea, bacteria and fungi as feed source. There are more than 75 bacterial genera capable to synthesize PHAs, that are also produced by archaea, fungi, plants and animals, in the soils and aquatic bodies.
In addition to the well known 3-hydroxybutyrate, more than monomeric constituents have already been identified [ 53 , 56 ]. The PHB synthesis can occur, for example, as follows: the bacteria are inoculated in a small batch reactor, along with sucrose, other nutrients and water, pH is adjusted and the temperature is raised.
The growing colony is transferred to successively larger reactors. After the initial growth of bacteria, the competition period starts, with bacterial storage of PHB in the cytoplasm. The molecular weight increases continuously up to reactor cooling and addition of solvent, what will cause cell lysis and dissolve PHB, which is then purified and dried. The powder obtained in the extraction process is transformed into pellets in an extruder. At the same time nucleating agents and plasticizers are added to improve processability and mechanical properties.
There are also successful attempts to develop genetically modified plants to produce PHAs [ 40 ], but the products obtained are very expensive, not being accepted by the market. Blend-stabilizing copolymers, with an intermediate chemical structure, may be obtained by separated synthesis, by transesterification or by the action of peroxides on the two components.
A significant product is the copolymer poly 3-hydroxybutyrate-cohydroxy-valerate , or PHBV Figure 2 , which presents lower crystallinity and rigidity than PHB, increasing the flexibility and the elongation capacity [ 57 ]. Some applications are: tubes for seedlings, injection and blown moulded containers, and films [for example, obtained with PHBH, or poly 3-hydroxybutyrate-cohydroxy-hexanoate ]. For medical applications, the price of PHAs is already acceptable, although it is still too high for the commodity market, such as for packaging.
Some important aspects to be improved in PHB are: strong degradation during processing PHB undergoes -elimination reactions, which cleave molecules and form chains with terminal unsaturation [ 60 ].
This is a consequence of the high crystallinity and the large spherulites formed, since the crystals nucleate slowly but grow fast. The PHAs may undergo simultaneously hydrolytic, oxidative and enzymatic degradation. The PHAs degrading microorganisms are widely distributed in the environment. Just as bacteria and archaea, fungi are also excellent decomposers [ 59 ]. In addition to their high degradative potential, many fungi have remarkable capacity to expand on the substrate surface, surrounding it with their hyphae, which release extracellular enzymes close enough to achieve the substrate [ 59 ].
PHAs are biodegradable in windrow composting, soil or marine sediments. The enzymes which are involved in the degradation of PHAs are depolymerases, hydrolases which may be intra- or extracellular and endo- or exoenzymes The enzymes may be classified as intra- or extracellular according their action inside or outside the cell, and also as endo- or exoenzymes, according their action inside or at the end of the substrate molecule.
They are usually induced enzymes whose expression is repressed in the presence of other carbon sources such as glucose and organic acids. PCL is a biodegradable polyester obtained from raw materials originating from petroleum, through ring opening polymerization of the lactone with suitable catalysts Figure 2.
It has good resistance to water and organic solvents. PCL is a polymer stable against abiotic hydrolysis, which occurs slowly with molecular weight decrease.
Its melting temperature is low, as its viscosity, facilitating its thermal processing. PCL may present spherulitic structure. It is a soft and flexible polymer, that may be used in blends with other biodegradable polymers, such as starch. A major global manufacturer is Solvay Capa, 5, t per year. Some applications are foamed food trays, bags, bioabsorbable medical items, replacement of gypsum in the treatment of broken bones, etc.
PCL may be degraded by many microorganisms, including bacteria and fungi, that are spread by soils and water bodies [ 56 ]. However, an initial stage of abiotic hydrolysis appears to be necessary [ 61 ].
The rates of hydrolysis and biodegradation depend on molecular weight and crystallinity [ 40 ]. Pronounced biodegradation occurs with molecular weights below about 5, g-mol Abiotic and biotic degradation take place preferentially in the amorphous phase. Enzymes from the two major classes of excreted esterases - lipases and cutinases - are able to degrade PCL and its blends [ 62 ]. Biodegradation causes surface erosion, without reduction of molecular weight [ 54 ].
PLA is an aliphatic polyester, derived from renewable resources, e. It is a polymer produced from lactic acid Figure 2 , which is obtained from the fermentation of various carbohydrate species: glucose, maltose and dextrose from corn or potato starch; sucrose from beet or sugar cane; and lactose from cheese whey [ 63 ].
The lactic acid monomer may be obtained by fermenting carbohydrate crops such as corn, sugar cane, cassava, wheat and barley, being eventually converted to lactide by means of a combined process of oligomerization and cyclization, with the use of catalysts. Mitsui used a solvent based process to remove water azeotropically in the condensation polymerization process.
Neste has obtained high molecular weight PLLA i. All the others use the dimer lactide process, with lactide ring opening polymerization. In the process using lactides, the additional step of dimerization of lactic acid increases production costs, but improves the control of molecular weight and end groups of the final polymer [ 38 ].
Through the stereochemical control of lactic acid ratio of D- and L- optical isomers , one can vary the crystallinity of PLA and also rate of crystallization, transparency, physical properties and even the biodegradation rate.
DL-PLA is used when it is important to have a homogeneous dispersion of the active species in the single-phase matrix, such as in devices for controlled release of drugs in the same manner that PLAGA copolymers. L-PLA is preferred for applications where mechanical strength and toughness are required, such as in sutures and orthopedic appliances.
The mechanical properties are somewhat higher than those of polyolefins in general. PLA is a hard material, similar in hardness to acrylics as methyl methacrylate. Because of its hardness, PLA fractures along the edges, resulting in a product that cannot be used. To overcome these limitations, PLA must be compounded with other materials to adjust the hardness [ 65 ]. The low glass transition temperature see Table 2 is the reason for the limited resistance of PLA to heat, making PLA inadequate for hot drink cups, for example.
PLA is suitable for frozen food or for packages stored at ambient temperatures. It is a polymer with consolidated use in the medical area, due to its biocompatibility and biodegradability in the human body. PLA-based resins may be modified to adapt to many applications, from disposable food-service items to sheet extrusion, and coating for paper [ 40 ]. The abiotic degradation of PLA takes place in two stages: a diffusion of water through the amorphous phase, degrading that phase; and b hydrolysis of crystalline domains, from the surface to the center [ 61 ].
The ester linkages are broken randomly. A semicrystalline material such as poly L-lactate presents a hydrolysis rate much lower than that from an amorphous material, such as poly D,L-lactate , with half-lives of, respectively, one or a few years, and a few weeks. The hydrolysis is self-catalyzed by the acidity of the resulting carboxylic groups [ 66 ]. PLA can not directly be degraded by microorganisms, but requires first abiotic hydrolytic degradation, so that the microorganisms mainly bacteria and fungi, which form biofilm can metabolize the lactic acid and its oligomers dissolved in water.
Abiotic hydrolysis takes place at temperatures above the glass transition temperature, i. Thus PLA is fully biodegradable in composting conditions of municipal waste plants, although it may need a few months to several years to be degraded under conditions of home composting, soil or oceans [ 35 , 63 , 67 ]. Furthermore, the PLA degrading microorganisms are not widespread in the environment [ 20 , 61 , 67 ]. The polymer passes the tests of compostability, provided that the thickness of the parts do not exceed around mm.
The extracellular enzymatic degradation consists of two steps: a the enzyme is adsorbed on the polymer surface, through its binding site; and b ester bonds are cleaved through the catalytic site of the enzyme [ 61 ]. The polymer chain ends are attacked preferentially. The biodegradation rate is a function of the crystallinity and the content of L-monomers [ 68 ].
Some enzymes proteases that may degrade PLA are proteinase K, pronase and bromelain. It is the simplest linear polyester, consisting only of a methylenic group between the ester linkages. It may be synthesized in a way quite similar to that of PLA, by the ring opening polymerization of glycolide, that is the cyclic dimer of glycolic acid.
Glycolate is copolymerized with lactate in order to obtain a copolymer with appropriate stiffness and elongation capacity known as PLAGA. The biodegradation of the PGA is usually faster than that of PLA, although an initial stage of abiotic hydrolysis appears to be necessary, since the polymer has a phase in the crystalline state and another in the amorphous glassy state [ 61 ].
PGA and its copolymers with lactic acid have very important medical applications: body absorbable sutures; ligaments reestablishment, through resorbable plates and screws; drugs of controlled release; grafting of arteries; etc.
Although the homopolymers PGA and D-PLA are not biodegradable, copolymers of glycolic acid and D-lactic acid, which may still contain L-lactic acid, are usually biodegradable by lipase enzymes [ 67 ].
The degradation of PGA seems to follow the same steps of PLA: diffusion of water into the amorphous region, with degradation and erosion; hydrolytic attack of the crystalline region; and biodegradation of monomers and oligomers dissolved in water. The aliphatic-aromatic polyesters have petrochemical origin, and are generally produced through traditional polycondensation reactions. They consist of aliphatic chain segments residues of 1,4-butanediol, and of adipic or succinic acid , which provide flexibility, toughness, and biodegradability and aromatic segments residues of terephthalic acid and 1,4-butanediol , which impart mechanical strength and rigidity.
PET, an aromatic polyester, decomposes very slowly in recalcitrant aromatic oligomers [ 69 ]. The degradation of the aliphatic-aromatic polymers may be oxidative, hydrolytic and enzymatic.
Elsewhere, governments are setting their own agendas towards the same goal. Companies have no choice but to follow new protocols. Fortunately, some are even leading the way, and they should be applauded. This is about eradicating plastic waste and pollution at the source, which is the mission of the New Plastics Economy Global Commitment , led by the Ellen MacArthur Foundation.
These companies include large consumer brands, plastic packaging producers and resource management specialists. One such company is Veolia. They are advising clients on limiting the production of all waste, but especially plastic waste. Their efforts are aimed at turning plastic into a secondary raw material and developing circular economy loops with manufacturers. You can find out who the Global Commitment signatories are here. Choose the businesses you want to be in bed with based on their environmental efforts and policies.
Doing so will show businesses that it is indeed environmentally and economically viable to take a stance and more importantly, effect change. Landfill is exactly what it sounds like.
However, the amound of land available is limited and suitable sites often fill up rapidly. Incineration of polymers releases a lot of heat energy, which can be used to generate electricity. However, there are problems with incineration. Carbon dioxide is produced, which adds to global warming.
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