Biodegradable polymers which when and why

However, with the increase in petroleum prices because of high demand and concern for the planet, the researchers began to study biopolymers. In Brazil, studies on biodegradable polymers were started in , through research on fermentative processes. Although it is still a recent observation, the Brazilian polymer market has good options with low environmental impact. The biodegradable plastic material can be used in several ways.

One of them is in medicine, in which polymers are used in the manufacture of implants, sutures, and bone fixations. Another advantage is that it is absorbed by the body in the same amount of time as tissue regeneration. A current example of a biodegradable polymer is polyhydroxyalkanoate PHA. Produced in bioreactors, it has bacteria that conserve biopolymers in cells. In the industry, a known alternative is green polyethylene PE , which besides having the same application as PE of fossil origin, captures CO2 from the atmosphere for production.

This type of biopolymer has been used in the production of automobiles, cosmetics, hygiene items, toys, and cleaning supplies. Polyamide PA are other examples of biodegradable plastics. As being polysaccharides, it is produced from corn, potato wheat or cassava.

In this case, the starch removed from the vegetables goes through a chemical process of destabilization and a rearrangement of molecules, generating the plastic. Injection, extrusion or blow moulding is suitable for processing PBS. Its applications include mulch film, cutlery, containers, packaging film, bags and flushable hygiene products.

Chemical structure of polybutylene succinate Okamoto et al. Because of the relatively low degradation rates, PBS can be copolymerized by adipate in order to increase the biodegradability. Poly butylene succinate- co -adipate PBSA is synthesized by the reaction of glycols with aliphatic dicarboxylic acids Fig. The succinic acid which is used to prepare this polymer is created by fermentation of sugar extracted from sugarcane or corn, therefore classifying it as a biobased material.

PBSA film has properties very similar to linear low-density polyethylene LLDPE and relatively high biodegradability, and is therefore suitable for a composting bag of kitchen waste Ren et al. Poly vinyl alcohol PVOH is the most readily biodegradable of vinyl polymers. It is readily degraded in waste-water-activated sludges. Unlike many vinyl polymers, PVOH is not prepared by polymerization of the corresponding monomer.

The monomer, vinyl alcohol, almost exclusively exists as the tautomeric form, acetaldehyde. PVOH instead is prepared by partial or complete hydrolysis of polyvinyl acetate to remove acetate groups Fig. It has a molecular weight of between 26, and 30,, and a degree of hydrolysis of PVOH is an odorless and tasteless, translucent, white or cream colored granular powder. It is used as a moisture barrier film for food supplement tablets and for foods that contain inclusions or dry food with inclusions that need to be protected from moisture uptake.

PVOH belongs to the water soluble polymers. In the context of the application, solubility and speed of solution are important characteristics. PVOH has excellent film forming, emulsifying and adhesive properties.

It is also resistant to oil, grease and solvents. It has high tensile strength and flexibility, as well as high oxygen and aroma barrier properties.

However these properties are dependent on humidity, in other words, with higher humidity more water is absorbed. The water, which acts as a plasticizer, will then reduce its tensile strength, but increase its elongation and tear strength. PVOH is the largest synthetic water-soluble polymer produced in the world. The prominent properties of PVOH may include its biodegradability in the environment. The generally accepted biodegradation mechanism occurs via a two-step reaction by oxidation of hydroxyl group followed by hydrolysis.

The isotactic material of PVOH preferentially degraded. The microbial degradation of PVOH has been studied, as well as its enzymatic degradation by secondary alcohol peroxidases isolated from soil bacteria of the Pseudomonas strain Jansson et al.

PVOH has been studied extensively because of its good biodegradability and mechanical properties. These properties have made PVOH as attractive material for disposable and biodegradable plastic substitutes. Its water solubility, reactivity, and biodegradability make it a potentially useful material in biomedical, agricultural, and water treatment areas, e.

Polyvinyl acetate, PVA , is a rubbery synthetic polymer. It is a type of thermoplastic and belongs to the polyvinyl esters family. Polyvinyl acetate is prepared by polymerization of vinyl acetate monomer free radical vinyl polymerization of the monomer vinyl acetate Fig.

The degree of polymerization of polyvinyl acetate typically is to The ester groups of the polyvinyl acetate are sensitive to base hydrolysis and will slowly convert PVA into polyvinyl alcohol and acetic acid.

Under alkaline conditions, boron compounds such as boric acid or borax cause the polymer to cross-link, forming tackifying precipitates or slime Dionisio et al. PVA reportedly undergoes biodegradation more slowly. Copolymers of ethylene and vinyl acetate were susceptible to slow degradation in soil-burial tests. The weight loss in a day period increased with increasing acetate content. Because PVOH is obtained from the hydrolysis of PVA, which can be controlled easily in terms of the extent of hydrolysis and the sequence of PVA and PVOH, a controlled hydrolysis of PVA followed by controlled oxidation should provide degradation materials having a wide range of properties and degradability.

Polyvinyl acetate is a component of a widely used glue type, commonly referred to as wood glue, white glue, carpenter's glue, or PVA glue. The stiff homopolymer PVA, mostly the more soft copolymer a combination of vinyl acetate and ethylene, vinyl acetate ethylene VAE , is used also in paper coatings, paint and other industrial coatings, as binder in nonwovens in glass fibers, sanitary napkins, filter paper and in textile finishing Chandra and Rustgi, Chemical structure of poly vinyl acetate Chandra and Rustgi, Several factors affect extent of polymer biodegradation that most impotents of them are polymer structure, polymer morphology, molecular weight, Radiation and chemical treatments.

Natural macromolecules, e. It is not surprising, then, that most of the reported synthetic biodegradable polymers contain hydrolyzable linkages along the polymer chain; for example, amide enamine, ester, urea, and urethane linkages are susceptible to biodegradation by microorganisms and hydrolytic enzymes.

Since many proteolytic enzymes specifically catalyze the hydrolysis of peptide linkages adjacent to substituents in proteins, substituted polymers containing substituents such as benzyl, hydroxy, carboxy, methyl, and phenyl groups have been prepared in the hope that an introduction of these substituents might increase biodegradability Savenkova et al.

Since most enzyme-catalyzed reactions occur in aqueous media, the hydrophilic—hydrophobic character of synthetic polymers greatly affects their biodegradabilities. A polymer containing both hydrophobic and hydrophilic segments seems to have a higher biodegradability than those polymers containing either hydrophobic or hydrophilic structures only.

A series of poly alkylene tartrate s was found to be readily assimilated by Aspergillus niger. However, the polymers derived from C 6 and C 8 alkane diols were more degradable than the more hydrophilic polymers derived from C 2 and C 4 alkane diols or the more hydrophobic polymers derived from the C 10 and C 12 alkane diols.

In order for a synthetic polymer to be degradable by enzyme catalysis, the polymer chain must be flexible enough to fit into the active site of the enzyme. This most likely accounts for the fact that, whereas the flexible aliphatic polyesters are readily degraded by biological systems, the more rigid aromatic poly ethylene terephthalate is generally considered to be bioinert Chandra and Rustgi, One of the principal differences between proteins and synthetic polymers is that proteins do not have equivalent repeating units along the polypeptide chains.

This irregularity results in protein chains being less likely to crystallize. It is quite probable that this property contributes to the ready biodegradability of proteins. Synthetic polymers, on the other hand, generally have short repeating units, and this regularity enhances crystallization, making the hydrolyzable groups inaccessible to enzymes. It was reasoned that synthetic polymers with long repeating units would be less likely to crystallize and thus might be biodegradable; indeed, a series of poly amide-urethane s were found to be readily degraded by subtilisin Zilberman et al.

Selective chemical degradation of semicrystalline polymer samples shows certain characteristic changes. This is attributed to the eventual disappearance of the amorphous portions of the sample.

The effect of morphology on the microbial and enzymatic degradation of PCL, a known biodegradable polymer with a number of potential applications, has been studied. Scanning electron microscopy SEM has shown that the degradation of a partially crystalline PCL film by filamentous fungi proceeds in a selective manner, with the amorphous regions being degraded prior to the degradation of the crystalline region. The microorganisms produce extracellular enzymes responsible for the selective degradation.

This selectivity can be attributed to the less-ordered packing of amorphous regions, which permits easier access for the enzyme to the polymer chains. The size, shape and number of the crystallites all have a pronounced effect on the chain mobility of the amorphous regions and thus affect the rate of the degradation. This has been demonstrated by studying the effects of changing orientation via stretching on the degradation Chandra and Rustgi, Biodegradation proceeds differently from chemical degradation.

Also, it was found that the differences in degradation rates between amorphous and crystalline regions are not same. The enzyme is able to degrade the crystalline regions faster than can methylamine.

Quantitative GPC gel permeation chromatography analysis shows that methylamines degrade the crystalline regions, forming single and double transverse length products. The enzyme system, on other hand, shows no intermediate molecular weight material and much smaller weight shift with degradation.

This indicates that although degradation is selective, the crystalline portions are degraded shortly after the chain ends are made available to the exoenzyme. The lateral size of the crystallites has a strong effect on the rate of degradation because the edge of the crystal is where degradation of the crystalline material takes place, due to the crystal packing.

A smaller lateral crystallite size yields a higher crystallite edge surface in the bulk polymer. Prior to the saturation of the enzyme active sites, the rate is dependent on available substrate; therefore, a smaller lateral crystallite size results in a higher rate of degradation. The degradation rate of a PCL film is zero order with respect to the total polymer, but is not zero order with respect to the concentrations of the crystallite edge material. The drawing of PCL films causes an increase in the rate of degradation, whereas annealing of the PCL causes a decrease in the rate of degradation.

This is probably due to opposite changes in lateral crystallite sizes. In vitro chemical and enzymatic degradations of polymers, especially polyesters, were analyzed with respect to chemical composition and physical properties. It was found quite often that the composition of a copolymer giving the lowest melting point is most susceptible to degradation Vert, The lowest packing order, as expected, corresponds with the fastest degradation rate.

Oxidation also occurs, complicating the situation, since exposure to light is seldom in the absence of oxygen. Initially, one expects the observed rate of degradation to increase until most of the fragmented polymer is consumed and a slower rate of degradation should follow for the crosslinked portion of the polymer.

A study of the effects of UV irradiation on hydrolyzable polymers confirmed this. Similarly, photooxidation of polyalkenes promotes slightly in most cases the biodegradation. The formation of carbonyl and ester groups is responsible for this change Miller and Williams, Processes have been developed to prepare copolymers of alkenes containing carbonyl groups so they will be more susceptible to photolytic cleavage prior to degradation. The problem with this approach is that negligible degradation was observed over a two year period for the buried specimens.

Unless a prephotolysis arrangement can be made, the problem of plastic waste disposal remains serious, as it is undesirable to have open disposal, even with constant sunlight exposure. For polyglycolide and poly glycolide- co -lactide , the pH of the degradation solution decreased as the process proceeded. Increasing radiation dosage shortens the time of the early stage.

The appearance of the drastic pH changes coincides with loss of tensile breaking strength. Similar effects via enzymatic and microbial degradation remain to be demonstrated Chandra and Rustgi, There have been many studies on the effects of molecular weight on biodegradation processes. Most of the observed differences can be attributed to the limit of detecting the changes during degradation, or, even more often, the differences in morphology and hydrophilicity—hydrophobicity of polymer samples of varying molecular weight.

Microorganisms produce both exoenzymes [degrading polymers from terminal groups inwards ] and endoenzymes degrading polymers randomly along the chain. One might expect a large molecular effect on the rate of degradation in the ease of exoenzymes and a relatively small molecular weight effect in the case of endoenzymes. Plastics remain relatively immune to microbial attack as long as their molecular weight remains high. Many plastics, such as poly ethylene, poly propylene and poly styrene do not support microbial growth.

Low molecular weight hydrocarbons, however, can be degraded by microbes. However, these processes do not function well if at all in an extracellular environment, and the plastic molecules are too large to enter the cell.

This problem does not arise with natural molecules, such as starch and cellulose, because conversions to low molecular weight components by enzyme reactions occur outside the microbial cell. Photodegradation or chemical degradation may decrease molecular weight to the point that microbial attack can proceed, however Chandra and Rustgi, The upper limits of molecular weight, beyond which uptake and intracellular degradation do not occur, have not been established for all alkane-derived materials.

Very slow degradation of paraffins, PE glycols, and linear alkyl benzene sulphonates occurs when the length of the polymer chain exceeds 24—30 carbon atoms. It could be concluded from these amply documented results that alkane-based plastics with molecular weights exceeding — daltons i.

Decreasing molecules of this size to biologically acceptable dimensions requires extensive destruction of the PE matrix. This destruction can be partly accomplished in blends of PE and biodegradable natural polymers by the action of organisms, such as arthropods, millipedes, crickets, and snails Santerre et al. Synthetic polymers are gradually being replaced by biodegradable materials especially those derived from replenishable, natural resources.

More than the origin, the chemical structure of the biopolymer that determines its biodegradability. Use of such biopackagings will open up potential economic benefits to farmers and agricultural processors. The principal field regards the use of packaging films for food products, loose films used for transport packaging, service packaging like carry bags, cups, plates and cutlery, biowaste bags, in agricultural and horticultural fields like bags and compostable articles.

Bilayer and multicomponent films resembling synthetic packaging materials with excellent barrier and mechanical properties need to be developed. Cross-linking, either chemically or enzymatically, of the various biomolecules is yet another approach of value in composite biodegradable films. Sustained multidisciplinary research efforts by chemists, polymer technologists, microbiologists, chemical engineers, environmental scientists and bureaucrats are needed for a successful implementation and commercialization of biopolymer-based eco-friendly packaging materials.

Undoubtedly, biodegradation offers an attractive route to environmental waste management. Their development costs are high and yet they do not have the benefit of economic scale.

Bio-based polymers have already found important applications in medicine field, where cost is much less important than function. It seems very unlikely that biodegradable oil based polymers will be displaced from their current role in packaging application, where cost is more important for the consumer market than environmental acceptability.

Biopolymers fulfill the environmental concerns but they show some limitations in terms of performance like thermal resistance, barrier and mechanical properties, associated with the costs. Then, this kind of packaging materials needs more research, more added value like the introduction of smart and intelligent molecules which is the nanotechnology field able to give information about the properties of the material inside the package quality, shelf-life, safety and nutritional values.

It is necessary to make researches on this kind of material to enhance barrier properties, to incorporate intelligent labelling, to give to the consumer the possibility to have more detailed product information than the current system. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.

Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications. Edited by Rolando Chamy. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists.

Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Introduction In developing countries, environmental pollution by synthetic polymers has assumed dangerous proportions.

Natural biodegradable polymers Biopolymers are polymers formed in nature during the growth cycles of all organisms; hence, they are also referred to as natural polymers. Biopolymers directly extracted from biomass 2. Polysaccharides For materials applications, the principal polysaccharides of interest are cellulose and starch, but increasing attention is being given to the more complex carbohydrate polymers produced by bacteria and fungi, especially to polysaccharides such as xanthan, curdlan, pullulan and hyaluronic acid.

Thermoplastic starch Starch is the major polysaccharide reserve material of photosynthetic tissues and of many types of plant storage organs such as seeds and swollen stems. Cellulose and its derivatives At present, cellulose is the most abundant polymer available worldwide with an estimated annual natural production of 1. Fibers Lignocellolosic complex Plant fibers include bast or stem or soft sclerenchyma fibers, leaf or hard fibers, seed, fruit, wood, cereal straw, and other grass fibers.

Chitin and chitosan Chitin is a polysaccharide found in the shells of crabs, lobsters, shrimps and insects or can be generated via fungal fermentation processes. Gums Gums are a group of polysaccharides that can form gels in solution upon the introduction of counterions. Polypeptides Proteins Proteins can be defined as natural polymers able to form amorphous three-dimensional structures stabilized mainly by noncovalent interactions.

Corn zein Zein comprises a group of alcohol-soluble proteins prolamins found in corn endosperm. Soy protein The major use of soybean in the food industry is as a source of oil, while soy protein concentrate and isolate are readily available as co-products of the oil processing industry Pszczola, Other proteins Prevalent types of plant and animal proteinous biopolymers have been discussed previously.

Biopolymers produced directly by natural or genetically modified organisms 2. Microbial polyesters The microbial polyesters are produced by biosynthetic function of a microorganism and readily biodegraded by microorganisms and within the body of higher animals, including humans. Polyhydroxyalcanoates PHAs Polyhydroxyalkanoates PHAs are a family of intracellular biopolymers synthesized by many bacteria as intracellular carbon and energy storage granules Fig.

Chem Eng J — Mater Horiz 4 3 — J Mater Chem A 3 9 — Polym Chem 5 8 — J Mater Chem B 4 2 — Nat Commun Mater 24 22 — Adv Funct Mater 24 32 — Green Chem 20 18 — Green Chem 20 11 — Macromolecules 28 18 — Michud A, Hummel M, Sixta H Influence of molar mass distribution on the final properties of fibers regenerated from cellulose dissolved in ionic liquid by dry-jet wet spinning.

Polymer —9. Green Chem 17 5 — J Mater Chem A 2 18 — Bioconjug Chem 28 5 — Sci Rep ACS Nano 11 6 — Biomacromolecules 19 8 — J Agric Food Chem 66 24 — ACS Nano 12 9 — Biomacromolecules 19 10 — ACS Omega 3 8 — Liu X, Gu X, Sun J, Zhang S Preparation and characterization of chitosan derivatives and their application as flame retardants in thermoplastic polyurethane.

Carbohydr Polym — Nature — Ind Eng Chem Res 53 13 — ACS Sustain. Eur Polym J — Bio Mater. Carbohyd Polym — Green Chem 20 9 — Westhues S, Idel J, Klankermayer J Molecular catalyst systems as key enablers for tailored polyesters and polycarbonate recycling concepts.

Adv 4 8. Mohammad Sahebjalal NC Twelve months dual antiplatelet therapy after drug-eluting stents-too long, too short or just right? Interv Cardiol 10 3 — Few polymers exhibit heterogeneous erosion. Most polymers undergo homogeneous erosion, means the hydrolysis occurs at even rate throughout the polymeric matrix. Generally these polymers tend to be more hydrophilic than those exhibiting surface erosion.

As a result, water penetrates the polymeric matrix and increases the rate of diffusion. In homogeneous erosion, there is loss of integrity of the polymer matrix. However, if a polymer is water soluble, that does not necessarily mean that it is biodegradable [ 4 ]. The release of drugs from the erodible polymers may occur by any of the mechanisms presented in fig. In mechanism 1, the drug is attached to the polymeric backbone by a labile bond, this bond has a higher reactivity toward hydrolysis than the polymer reactivity to break down.

In mechanism 2, the drug is in the core surrounded by a biodegradable rate controlling membrane. This is a reservoir type device that provides erodibility to eliminate surgical removal of the drug-depleted device. Mechanism 3 describes a homogeneously dispersed drug in the biodegradable polymer.

The drug is released by erosion, diffusion, or a combination of both. Fig 2: Schematic representation of drug release mechanisms In mechanism 1, drug is released by hydrolysis of polymeric bond. In mechanism 2, drug release is controlled by biodegradable membrane. In mechanism 3, drug is released by erosion, diffusion, or a combination of both. Historically, polyanhydrides were developed in textile industry during the first half of the 20 th century as alternate fiber materials.

The anhydride linkages of these polymers are, in general, more hydrolytically liable than the polyester bond. In order to achieve a surface eroding mechanism, polymers are generally prepared from very hydrophobic monomers in order to minimize water penetration into the bulk of the device6. By doing this, hydrolysis of liable anhydride linkages would be restricted to the outer exposed surfaces of the polymer device.

A wide variety of aromatic and aliphatic monomers are used to prepare surface eroding polyanhydride polymers [ 7 , 8 ]. Polymers with increasing hydrophobicity can be made from aromatic monomers including phthalic acid and various carboxyphenoxyalkanes such as poly[1-bis p -carboxyphenoxy methane] CPM , poly[1,3-bis p -carboxyphenoxy propane] CPP and poly[1,6-bis p -carboxyphenoxy hexane] CPH.

High-molecular-weight polyanhydrides are usually synthesized by first converting the dicarboxylic acid monomer to mixed anhydride prepolymers using acetic anhydride followed by polymerization of prepolymers using polycondensation reaction in the melt.

Typically, homopolymers are not studied because they posed unfavorable characteristics rendering their handling and manufacture difficult. By varying the ratio of the hydrophobic moiety CPP and sebacic acid SA , controlled degradation rates, from days to years, have been achieved.

The release of number of drugs from polyanhydride matrices has been studied including p -nitroaniline, ciprofloxacin [ 8 ], cortisone acetate, insulin [ 9 ] and variety of proteins. Poly ortho esters have been under development since [ 10 , 11 ].

Poly ortho ester I, the first such polymer prepared, has been developed at Alza Corporation. Poly ortho ester I is hydrolysed when placed in an aqueous environment. The use of a crosslinked poly ortho ester to release 5- fluorouracil 5-FU and Luteinizing hormone releasing hormone LHRH analog intended for glaucoma filtration surgery and contraception, respectively, has been described [ 13 ].

The crosslinking density and a readily erodable component, 9,dihydroxystearic acid, in the polymer controls the release kinetics. A near-constant release is observed in some cases as a result of the increasing permeation rate caused by the cleavage of the crosslinking bonds.

Release of LHRH on the other hand follows a biphasic profile. The initial release corresponds to diffusional release, and later to the hydrolytic liberation of the protein that has been chemically bound to the matrix during fabrication. Studies focusing on the erosion characteristics of catalyzed poly ortho ester matrices [ 14 ] and the effect of crosslinking and base incorporation on the polymer degradation behavior, have also been reported [ 15 ]. Poly ortho ester III is a semisolid material that has been shown to be highly biocompatible and is currently being investigated as an adjunct to glaucoma filtering surgery and other ocular applications.

However, the polymerization is difficult to control and is not readily scaled up. Now-a-days poly ortho ester IV can also be easily prepared in a highly reproducible manner. It is currently under development for a variety of applications, such as ocular delivery, protein release, post-operative pain treatment and post-operative cancer treatment [ 16 ].

There are two major classes of phosphorus containg polymers, the phosphazenes and phosphoesters [ 17 ]. The class of phosphoesters based polymers includes polyphosphonates, polyphosphates and polyphosphites. The copolymer, poly lactide-co-phosphate exhibited faster degradation as the phosphate content increased.

The class of poly phosphazenes were first explored as drug carriers in to deliver naproxen [ 18 ]. Previous studies suggested that the degradation products of this polymer consist of ammonia, glycine or alanine, ethanol or benzyl alcohol, phosphate, and the side group substituents. It appears that polymers would be attractive candidates for pendant delivery system [ 19 ]. The first biodegradable synthetic polymer and bioabsorbable suture material was poly glycolic acid PGA , which appeared in belongs to this class [ 20 , 21 ].

The prospective applications include devices to treat cancer, drug addiction, and infection, as well as drugs for contraception, vaccination, tissue regeneration and cartilage tissue engineering. The use of PGA homopolymer is limited to suture material because of its high crystallinity and absence of practical solvent. There are two main routes to synthesize these aliphatic polyesters [ 22 ], polycondensation of bifunctional hydroxy acids and ring opening polymerization of cyclic esters monomers.

With regard to monomer synthesis, the synthesis of lactides and glycolide consists of two steps, Lactic acid or glycolic acid is first polycondensed to yield low molar mass oligomers.

Then, oligomers are thermally depolymerised to form the corresponding cyclic diester, which is recovered by distillation at low pressure. Catalysts such as zinc metal or zinc oxide are used in the second step to improve the yield. For polymer synthesis, the conversion of cyclic monomers to polymer chains requires the use of initiators or catalysts.

Two compounds are used industrially, namely Tin II 2-ethyl hexanoate stannous octoate and Zn metal.