538 POLIMERY 2002,47, nr 7-B

EMO CHIELLINI-), PATRIZIA CINELLI, SALVATORE D'ANTONE, VASSILKA IVANOVA ILIEVAUniversiĘ of Pisa, Department of Chemistry & Industrial ChemistryVia Risorgimento 35, 56726 Pisa, Italy

Environmentally degradable polymeric materials (EDPM)in agricultural applications - an overview

Summary - Owing to their low production cbst, good physical propertiesand lightweight, plastic objects have slowly substituted glass, paper and me-tals in severai fieJds of application including agriculture. At the same time, thecurrent huge global production of plastics (200 million tons/year) has gene-rated an enormous environmental concerns, mainly related to the waste gene-ration by plastic packaging, which are responsible for 35-40% share of an-nuai plastics consumption. Where recovery of plastics is not economicallyfeasible, viable, controllable or attractive, plastics often remain as litter. This isthe case in most of agricultural applications of polymeric materiais. The mar-ket for biodegradable polymers is at this moment focusing on products inwhich biodegradability provides beneficial effects (e.g. waste-disposal, recy-cling) and a number of biodegradable materials are already being marketed orare close to market introduction and customer acceptance. This overview ismeant to provide an outline on the history and recent developments in biode-gradable polymeric materials applied in agricultural practices with particularreference to the mulching segment. Special attention has been devoted tomaterial based on renewable resources or utilization of waste products fromthe agroindustrial sector, thus suggesting cost-effective and environmentallysound solutions to specific social needs.Key words: environmentally degradable plastics, plastic waste, agriculturalapplications, mulching.

PLASTICS WASTE MANAGEMENT AND EPDM _GENERALREMARKS

The characteristics of strength and durability de-signed into plastics, in order to meet end-use require-ments, coupled with the problems associated with theirpost-consumption disposal, played a significant role inoffering new options alternative to plastics recycling andlandfilling practice. Particular effort has been devoted tooptions based on the recovery of plastic waste as rawmaterial or energy source and, whenever applicable(biodegradable materials), aią a biorecycling [1]. Severaltechnologies have been recognized as viable optionsalong with environmental degradation, such as recy-cling of plastic materials, including mechanical recy-cling, recycling to monomeric components followed byrepolymerization to the same or ner / polymeric mate-rial, recycling to hydrocarbon feedstocks by pyrolysis,direct incineration and composting. Each of these dis-

posal technologies is playing a role in polymer wastemanagement [2]. The choice among them depends onseveral factors, including available processing facilities,collection of waste material, cost of new polymers, pro-perty requirements, and specific service reponses.

Utilization of plastics in agriculture in the form o{mulch films, greenhouse components, irrigation tubesand general-purpose containers continue to generateplastic waste in large quantities. Currently, any systema-tic collection of plastic waste for recycling and/or dis-posal is rather expensive and limited only to certaincommunities. Moreover, when plastics are contaminatedwith soil, foods or other chemicals their recyciing israther difficult and for this reason only 2'k of the plasticwaste is nowadays recycled in the United States.

in the European Community legislation, directiveshave been so far issued on wastes [3] on dangerous'nrastes [4], on waste from packaging applications [5] inwhich waste has been classified depending on its originand its potential danger. This new classification has in-troduced a new category of "special wastes". Waste de-riving from agricultural and agrochemical activities has

-) To whom correspondence should be addressed,

chlmco@dcci.unipi.ite-mail:

POLIMERY 2002,47, nr 7-B 539

been placed in this category with the need of post-con-sumption reclamation and further treatment in control-led infrastructures, thus leading to substantial increaseof disposal costs, which in some cases may be evenhigher than the cost of the virgin material itself.

The biodegradability and utilization of agriculturalpolymeric materials is a topic rising in importance overthe last few years [6]. industries have started to developseveral products based on environmentally degradablepolymeric materials to be applied in agricultural prac-tices such as mulching films, green houses sheets, lami-nates, containers, seedling pots, and for applicationssuch as soil structurization and controlled release systemof chemicals (fertilizers, herbicides, growth stimulantsand pesticides).

Globally increased agricultural productivity has pro-moted the utilization of agricultural products in envi-ronmentally acceptable plastic materials. The usefulnessof a variety of agricultural coproducts as commodityplastics substitutes is under consideration of researchersin academies and industries [7]. The use of EPDM basedon agricultural wastes or crop surplus to be used in agri-culture applications or other merceologic commoditysegments appears as an exkemely promising approachfor contributing to the soiution of plastic waste manage-ment.

APPLICATION OF POLYMERIC MATERIALSIN AGRICULTURE

Polymeric materials started to be applied in agricul-tural practices from the sixties, mostly in replacing glassas greenhouses and tunnels covering. Thus, plasticsmade possible the introduction of mulching films, anovel agricultural technology not applied before the pro-duction of plastic films started. The polymeric materialsused consisted mainly of polyethylene and poly(vinylchloride).

All main classes of polymeric materials, i.e., plastics,elastomers, fibers, coatings, and water-soluble polymers,are presently utilized in applications including control-led release of pesticides, soil conditioning, plant protec-tion, seed coating, gel planting, water transport andpackaging [8]. New technology based on polyethylenehad especially a strong impact on the growing of softfruits and vegetables 19-121.

Although plastics in agriculture comprise less than2'/. of total plastic usage in Europe and about 4% in theUSA, much more is used in Mediterranean countries(Spain 87n, Israel 72"k) and in China (20%) where agri-culture is more intensive [10].

The assessment of structure-property-performancerelationships in polymer selection for agricultural ap-plications is of vital importance, including parameterssuch as strength, toughness, weathering, thermal ex-pansion, light and thermal transmission, biodegradabi-lity and permeability to oxygen, carbon dioxide, and

water. Table 1 summarizes main agricultural applica-tions of degradable polymeric materials of synthetic ori-gin mainly derived from fossil fuel feedstocks and ofnatural origin, derived from renewable resources.

T a b I e 1. Applications of degradable polymeric materials ina8riculture [13]

Application Polymeric materials

Plant growing sheets Polyethylene-)Poly(lactic acid)Poly(vinyl alcohol)StarchCelluloseLigninFruit by-productsSoy proteinPectinChitosan

Soil amendments Poly(amino acids)Polyes ters

Poly(vinyl alcohol)Carboxym ethylcellulose

Fertilizers and growth stimulants Proteic eluate from tanningindustry

Poly(aspartic acid)

Since research is aimed at developing polymers forapplications in which they offer unique advantages overthe competitive alternatives, interest in biodegradableplastics used in agriculture, has grown, as costs may bereduced by using photo-thermally or biologically de-gradable polymers, thus avoiding the labor intensiveand costly step of collection and sorting typical in recy-cling. With this point in mind degradable polymersbased on polyethylene started to be investigated sincethe 1970s [13-23] and led to the development of de-gradable materials, as recently reviewed by Scott [23],and listed in Table 2.

Much effort has been focused in recent years to de-velop environmentally compatible polymeric materials

T a b I e 2. Degradable materials based on polyolefins

Category Polymeric material Commercial name

Photolitic polymers Poiy(ethylene-co-carbo nmonoxide)

Poly(ethylene-co-vinylketone)

E-CO

Ecolyte

Oxodegradablepolymers

Polyethylene PlastorTDPAGPI)

Polyethylen/starchblends

PE-starch Coloroll,St LawerenceStarch

.) Photodegradable, thermally degradable.

540 POLIMERY 2002, 47, nr 7-B

by starting from renewable resources as an alternative topetroleum-based synthetic polymers. As an additionaladvantage, some renewables are comparatively less ex-pensive, environmentally friendly and naturally biode-gradable. Particularly, materials such as annual crops,agricultural waste and/or by-products are a good sourcefor the formulation of environmentally compatible poly-meric materials.

A more detailed description and categorization of thepolymeric materials used in specific segments of agricul-tural practices is reported below, by their specific appli-cations.

Mulches

In the past, mulch practice has been performed by theuse of natural materials such as straw and leaves to pro-vide an insulating layer around the roots of vegetablesand soft fruits. Actually, the use of plastic sheets or filmsin mulching is the largest single application of plastics inagriculture. Mulch controls radiation, soil temperatureand humidity, weed growth, insect infestation, soil com-paction, and the degree of carbon dioxide retention. Insome cases, weed control has been reported because ofsolar heating plastic fllms mulches (solarization). Notonly do mulch-grown crops mature faster, but alsoyields are increased and in most cases the product iseasy to harvest and cleaner with evident returns on theproduction costs [23].

Table 3 specifies examples of crop yields obtainedwith and without mulching as reported by Scott in hisrecent publication on the environmental impact of poly-mers [131.

T a b I e 3. The effect of mulching films on crop yields [131

Crop Location TreatmentYield ")

kgIncrcase

Musk melon Nelv Brunswick Bare groundMulched

62.7

92.6 47

Tomatoes Oregon Barc groundMulched

10.5

15.2 45

Bell peppcr Rio Grande Barc groundMulched

1356

OOJJ 389

") Referred to: 7 plant (mellon), 1 plant (tomatocs), t hectare (pepper).

The use of black mulching films with eiimination ofweeds and avoidance of soil compaction eliminates theneed for cultivation, thus preventing root damage andplants stunting or killing. Fertilizer and water require-ments are also reduced, the use of plastic mulches resultsin 50% saving of irrigation water and as much as 30ohsaving in nitrogenous fertilizers even in temperate cli-mates [13]. Low density polyethylene, poly(vinyl chlo-ride), polybuĘlene, and copolymers of ethylene with vi-

nyl acetate have been generally used for mulching. Justin 1998 the worldwide yearly consumption for polyethy-lene mulch film alone r /as around half million tons [24,251.

The fact that plastic do not degrade as fast as thepreviously used natural materials may sound as an ad-vantage because it ensures a coherent protective barrierbetween the roots of the plants and the environmentthroughout the growing life of the plant. If left in place,however, conventional plastic films can cause problemsduring harvesting or during cultivating operations inthe following year [26]. Thus, many soft fruit crops arenow hźirvested automatically with a procedure leavingstems and leaves on the ground. The presence of plasticfragments mixed with the crop residue may clog the en-gines of harvesting machines and turns automatic collec-tion into a difficult task. Removal and disposal are costlyand inconvenient. Attempts to promote collection sys-tems, recycling technology and applications for the recy-cled material deriving from mulching films have showna series of difficulties. Transportation of the long strips ofthe films, compaction and washing were found to be themost critical and labor intensive steps in the process,because of the films deterioration and the high level(30-40% by weight) of soil contamination [27]. More-over many landfills reject mulch films because of pesti-cide residues for which they must be treated as hazard-ous waste. Furthermore, nowadays the thickness ofmulching films can be as low as 8-10 Lrm that makesthem too fragile to be easiiy and efficiently collectedfrom the field after cropping.

Interest in the development of biodegradable or pho-todegradable films with short service lifetimes and even-tually controllable has grown. Degradable mulchesshould break down to small brittle pieces, to passthrough harvesting machinery without difficulty andshould not interfere with subsequent planting opera-tions. The induction time therefore must be variable,predictable, and reproducible [28]. Crop yields could beconsiderably reduced if the film degrades before end ofthe growing season. In addition, toxic residues are unac-ceptable, processing stability must not be affected byfilm components and storage must not modify the ulti-mate mechanical and physical product properties. Forthese reasons thin photo-biodegradable polyethylenefilms are presently used for crops, which are supposed tobe automatically harvested.

Table 4 presents some examples of biodegradablepolymers applied in mulching practices.

Photodegradable films have been proposed as de-gradable mulching films, such as poly(1-butene) [29].More recently, interest in the development of new pho-todegradable films has mounted in mainland China andTaiwan t30-321. As reported before, in these countriesthe plastic consumption for agricultural practice is veryhigh (20%) [33]. In such materials a polyolefin is blendedwith a modified starch as coupling agent, a photode-

POLIMERY 2002, 47, nr 7-B 547

grading agent, an oxidation accelerant, a self-oxidant,and a degradation controlling agent. In consequence, de-bris of the polyolefines tend to accumulate in the soilafter degradation and disintegration of the films.

T a b I e 4. Biodegradable polymeric materials used in mulchingpractices

Synthetic polymers Natural / artificial polymers

Photodcgradable polyethylenePoly(vinyl alcohol)Poly(lactic acid)Poly(hydroxy butyratc)Poly(hydroxy alcanoates)

Poly(caprolactone)

Starch, cellulose, kraft paperPectin, fruit (pit and seed), chitinWheat gluten, cereals wasteWood, sugar beet, bagasseSoy protein, gelatin, protein

hydrolizateCellulose esters

Crosslinked amino acid

In another approach, degradable mulching filmswere prepared by biending synthetic polymers withnatural filiers such as starch. Films based on starchblended with: polyethylene [sł], oo1u,rrinyl alcohol)[35], poiy(ethylene-co-acrylic acid) (EAA) [36-38] andpoly(vinyl chloride) (PVC) [39] were then developed.Thus, in some of these materials only the starch compo-nent was degraded while the continuos matrix repre-sented by the synthetic polymer rvas accumulating inthe environment. In starch-polyethylene films, frag-ments resulting from film deterioration, may requiredecades to completely biodegrade; moreover, the effectof long term soil exposure to polyhydrocarbon debris islargely unknown [40]. For these reasons the interestmoved toward blends based on starch and syntheticpolymers, which are also biodegradable such as poly(vi-nyl alcohol) [47,42], polycaprolactone (Materbi) [43] andother synthetic polyesters.

Advantages resulting from the use of material fromrenewable resources as fiilers in blends with syntheticdegradable polymers have induced interest in a widegroup of natural polymers, such as lignocellulosic mate-rials, pectins, chitin, animal and vegetal sources.

Poiy(vinyl aicohol) has been biended with pectin [44,451, chitin [46, 471, sugar cane bagasse and fruit juiceextraction by-products such as apple and orange wastes[48], soy protein [49], gelatin [50,51].

Use of biodegradable thermoplastic polymers fromrenewable resources as the continuous matrix is also fo-cusing recent research activity [52-56]. Several patentshave been filled for and issued dealing with polyestercompounds from renewable resources for agriculturalfilms production, also in blends with natural polymers157-5e).

Up to now, such polyesters were produced biotech-nologically from refined raM/ materials (e.9. glucose andsodium propionate). For example, polyhydroxyal-kanoates (PHAs) can be produced from saccharides, al-

cohols, and low molecular weight fatty acids. Polyesterscan be produced by a much cheaper method startingfrom agricultural wastes (e.9. molasses, maltose, glycerolphase from biodiesel production, whey), as long as thesematerials have a known composition and are availablein appropriate quantities [60J.

Mulching practice based on the use of recycled mate-rials has also attracted interest as an alternative to plasticfilms usage [61]. Therefore, farmers sometimes use or-ganic mulches such as paper, leaves, straw. Kraft papercoated with polymerized vegetable oils has been re-cently proposed as biodegradable mulch 162,631.

Films and/or laminated films produced with naturalpolymers have been also the object of research activity.Thus, films have been claimed as fabricated by chitosanand pectin [64], starch and pectin [65], soy protein andstarch 166,671.

Composite films have been developed in our labora-tories based on natural and synthetic degradable poly-mers blended with waste agricultural materials. Mate-rials such as sugar cane bagasse have been blended withnatural polymers such as gelatin waste from pharma-ceutical industry. Prepared composites had mechanicalproperties [68] and degradation times [69] interesting foragricultural applications. Thus, animal and vegetableprotein based materials possess an intrinsic agronomicvalue because of their fairly high nitrogen content(70-12'/.).

Similarly, interesting properties have been reportedfor composites films based on poly(vinyl alcohol) andwaste products from orange and apple juice extraction1701.

Other applications

Plastic films and sheets have been found suitable forapplication in greenhouses [8]. Plastics are lightweight,and appreciably durable materials, permitting a numberof structural designs to be implemented, including air--supported buildings, which turn to be less expensiveand more easily maintained than glass greenhouses.

Greenhouses must allow transmission of solar radia-tion to soil and plants and must also be able to retain there-irradiated infrared energy at night. Plastics used forthe manufacturing of greenhouse components must beimpermeable to radiation between 7 and 55 pm in theinfrared region and possibly must have insulating ca-paciĘ, LlV-stabiliry fungi resistance, and COz and waterpermeability.

Polymers utilized for greenhouse enclosures can beboth rigid as well as flexible including poly(vinyl chlo-ride), polyethylene, ethylene/vinyl acetate copolymers(EVA), poly(ethylene terephthalate), poly(methyl metha-crylate), polycarbonate, polystyrene, styrene / acryloni-trile copolymers (SAN), and may include also celluloseand a variety of fiber-reinforced composites, which havebeen considered for this purpose.

542 POLIMERY 2002, 47, nr 7-B

Plastics used in greenhouses must be resistant to theenvironment, so stabilization is extremely important inthe cost competing with glass usage. This constitutes avery active area of research focused on improvement inthe durability of polyethylene against deterioration bylight and heat.

The capacity of certain polymers to hold water allowsfor their spraying and blowing alone in slurries withother mulching materials and nutrients for seed coatingor soil conditioning.

In seed coatings a hydrophilic polymer is usuallycoated directly onto the seed surface. After planting, thepolymer absorbs water and thereby increases the rate ofgermination as well as the percentage of germinatedseeds. However, depending on the application, the typeof polymeric coatings can be varied to delay germina-tion, inhibit root growth, control pests, fertilize, and bindthe seed to the soil. Agar, water-soluble cellulose ethers,such as carboxymethyl-, hydroxyethyl-, and hydroxy-

methylcellulose, and hydrolyzed starch-g-polyacryloni-trile copolymers (HSPAN) have been studied to thegreatest extent in seed coating. HSPAN coatings havebeen applied to a variety of seeds, including soybeans,cotton, corn, sorghum/ sugar beet, and a number ofvegetables [711.

Polymers may also be present as tackifiers to helpholding the mulch in place once applied. In some cases,a type of thatch is formed that protects seeds and soilagainst erosion. Hydrophilic polymers, such aspoly(acrylamide), poly(vinyl alcohol), carboxymethyl-cellulose, and HSPAN have been used as soil conditio-ners in fechniques called hydro-mulching [8, 71.,72).

The effect on the environment deriving from the useof fertilizers is also an issue of global concern. Biode-gradable polymers such as thermally synthesized poly-aspartate [73] have been proposed for this application.

Kolomaznik et ąI. l74l ProPose protein hydrolysatefrom tanning industry for use as an organic nitrogenous

Company

BayerBioplastic, Inc.

Biotec

Bird-X inc./Eco Turf Inc.

BSL.)

Cargill Dow ChemicalsChronopol Inc.

DuPontEastmanIdroplast

Kemira Agro OyMarshall Plastic Film, IncMetabolix, Inc.MonsantoNATCO h)

Nova Chcm Ltd.

NovamontNovon

Poly ExpertPPI, Inc.i)

Solvay Sa

TPS, Inc.j)

Union Carbidc Corp.

Materials

Polyester amidePCLU), StarchTPStarch b)

Cellulose acetatePCL-StarchDegra-Novon@

Starch acetatePLA.t)PLAd)Polyester resins

Copopolyesters of diacids and glycolsPVA")PVA")nsDegra-Novon@PHAs)PHAWheat-starchSuper absorbentCarboxymethyl derivatives of chitosanCarboxymethyl derivatives of chitosanPCL-starchModlfied starch, other chemicalsModified PVAStarchNovon Starch based polymerPCL alloysUrcthane acrylics, styrene, vegetable oilsPCLPVAPCL

"' PCL = Polycaprolacto,,e, b'TPStarch = Thermoplastic starch,') BSL = Buna Sow Leuna Olenfinverbund, J) PLA = Poly(lactic acrd), ") PVA =

Poly(vinyl aicońoll, 0 ns = not specified, g) PHA ='Polyhydroxyalkanoates, h) NATCO = Natural Absorbcnt Technology Co', i) PPT, Inc. = Planel

Polymer Tcchnologics, Inc., I'TPS, lnc. = Texas Polymer Services, Inc.

T a b I e 5. Companies involved in the manufacturing of agricultural products using biodegradable polymers

BAK 1095@

-TMŁnvarBioplastoBioflex@

@DroPur

Turffaks@^ ,,@SCOnaCCll

EcoPLAHeplonrNtBiomax@Eastar BioAgriBag@

SoilBag@f)

ns

NS

nsBiopol@E-ZTurPóSta-WctlvNutri Save@

Phero Release@

MaterBirMDegra-Novon@Aqua-Novon@Poly-Novon@nsEnviroPlastic@EnviroPlastic@

CAPA@6OOTMvlnex

TONE@

Films and sheets

Mulch filmsFilms and sheets

Plant pots.Trays for cultivating plants

Turf and erosion controlFilms, flower potsMulch fims, green houses pots

Plant growth stimulant, filmsMulch containers, plant pots

Seed mats, root coversChemicals distributionWrap plant roots

Controlled releaseAgricultural filmsLawn and leaf bags, filmsMulch films, plant potsBiodegradable seeded grass

Mats for instant lawnsCoating for fruit and vegetables

Delivery device for pheromones for pest controlMulch films, nursey potsMulch filmsSanitary applicationsMulch filmsMulch filmsMulch filmsControlled release of fertilizersControlled release of fertilizersPackaging for chemicalsMulch films, pots, controlled release of chemicals

POLIMERY 2002,47, nr 7-B 543

fertilizer or fertilizer component, and use in the manu-facturing of biodegradable polymers for agriculturesowing tapes.

Table 5 summarizes some examples of companies in-voived in the manufacturing of agricultural products us-ing biodegradable polymers and the relative recom-mended application.

CONCLUSIONS

Modern agricultural technology is ever more de-manding for agrochemical materials and manufacts thatare ecocompatible and attainable at a reasonably com-petitive price. In that respect, introduction of biodegrad-able polymeric materials in a large variety of agriculturalapplications appears to be a viable solution, proviCedthese materials may be derived from cheap raM/ mate-rials and eventually from agroindustrial waste or a suit-able combination of natural resources and fossil fuel.

The extremely active academic and industrial re-search on the use of biodegradable polymers for agricul-tural applications has led to the introduction of severalproducts on the market. These products based on biode-gradables are supposed to be applied in agriculturalpractices such as mulching films, green house sheets,laminates, containers and for application as soil struc-turization and controlled release of chemicals such asfertilizers, herbicide.

The number of biodegradable items for agriculturalapplication entitled to enter the market is going to in-crease also in consideration of the role and impact thatthe so cailed "biological agriculture and horticulture"are going to assume in the near future.

REFERENCES

[1] Doane W. M.: l. Polym. Mater.7994,1'1'.,229.l2lFeIlH.: Macromol. Symp., 7998, 127, 7. [3] Council Directive97/156{EEC of 18 March 1991 amending Directive75/442/EEC on waste, http://europa.eu.int/ [4] CouncilDirective 97 / 689 /EEC of 12 December 1991 on hazard-ous waste, http://europa.eu.int/ [5] European Parlia-ment and Council Directive 94/ 62/EC of 20 December7994 on packaging and packaging waste, http/leuropa.eu.int/ 16l "Agricultural and Synthetic Poly-mers. Biodegradability and Utilization" (Eds. Grass J. E.,Swift G.), ACS Symposium Serie 433, Washington DC1990. l7l "Polymers from Agricultural Coproducts"(Eds. Fishman M. L., Friedman R., Huang S. J.), ACSSymposium Serie 575, Washington DC 7994. [8] McCor-mick C. L.: "Agricultural Applications" Chapter in: "En-cyclopedia of Polymer Science and Engineering", Vol. 1,

2nd Ed., ]ohn Wilet & Sons, New York 1984. l9l GileadD., Scott G.: "Developments in Polymer Stabilization"(Ed. Scott G.), Elsevier Applied Science Publisher, Lon-don 7982, Chapter 4. [10] Scott G.: Trends in Polym. Sci.7997 , 5, 367 .

[11] Gilead D.: "Degradable Polymers: Principles andApplications" (Eds. Scott G., Gilead D.), Chapman &Hall: London1.995, Chapter 10. [12] Fabbri A.: "Degrad-able Polymers: Principles and Applications" (Eds. ScottG., Gilead D.), Chapman & Hall: London 1995, Chapter11. [13] Scott G.: "Polymers and the Environmen{' RSCPaperbacks, UK7999,p.Ża.U,a] Guillet E' J.: "Polymersand Ecological Problems", Plenum Press, New York7973. [751Scott G.: l. Polym. Sci. Symp. 7976,57,357.1761Omichi H.: "Degradation and Stabilization of Polyole-fins" (Ed. Allen S. N.), Applied Science Publisher, Lon-don 1983, Chapter 4.llTl "Chemistry and technology ofbiodegradable polymers" (Ed. Griffin I. G. L.), BlackieAcademic and Professional, London 1994, Chapters1-3. [18] Scott G.: "Biodegradable Plastic and Poly-mers" (Eds. Doi Y., Fukuda K.), Elsevier Science BV, Am-sterdam 1994,p.79.119) Scott G.: Polym. Deg.}tab.2000,68, 1. [20] Scott G.: "Degradable Polymers: Principlesand Applications" Chapman & Hall, London 1995,Chapter 9.

[21] Guillet l: Plast. Eng. 7974, Aug, 47. [22] Wiles D.M., Cermak B. E., Gho J. G., Hare C. W.: l. Enuironm.News 1998, 8, No.6' [23] Scott G.: Biamącromolecules 2,

2007, 675. [24] Fabbri A.: "Le Materie Plastiche e l'Am-biente", AISTM, Grafis Edizioni, Bologna 1990. [25] Jen-sen M. H.: Presentation at theZ7th National AgricuituralPlastics Congress, 7998. 126) Dever M., Lambdin P. L.,Ownley B. H., FairN. B.: Bio/Environmentally Degrad-able Polymer SocieĘ 5th annual meeting, NashvilleSept. 22,7996. I27) Llop C., Perez A.: Mąkromol. Chem.,Macromol Symp.7992,57,115. [28] Gilead D.: Chemtec1985, 15, 299. I29l Potts J. E., "Plastic EnvironmentaliyDegradable" Chapter in: "Kirk-Othmer Encyciopedia ofChemical Technology" ,3rd ed., Suppl. Vol., john Wilet &Sons' New York 1984, p.626' l30] Chi:ną Pątent 7 793 026A (1998).

I3I] Chiną P atent 7 239 725 A (7999).[32] Chiną P ąten t 7

235 774 A (1999). t33] u. S. Pątent 4 076 777 (7977)' I34]Otey F. H., Mark A.M., Mehltretter C. L., Russell C. R.:lnd. Eng. Chem. Res, 7974, 13,90. [35] Lahalih S. M.Akashah S. A, Al-Hajjar F. H: lnd. Eng. Chem. Res.,7987,26,2366. [36l otey F. H, Westhoff R. Ę Russell C.R.: lnd.Eng. Chem. Res. 7977 ,16,305. [37] Otey F. H., Westhoff R.P., Doane W. M.: lnd. Eng. Chem. Res. 7980, 19,592. [38]Otey F. H., Westhoff R. P., Doane W M.: lnd. Eng. Chem.Res. 1987,26,7659. [39] Westhoff R. P., Otey R. H.,Mehltretter C. L., Russell C. R.: Ind. Eng. Chem. Prod. Res.Dea. 7974, 13, 1.23. [40] Albertsson A.C., Karlsson S.:

I. Appl. Polym. Sci. 7988, 35, 7289.[41] Lawton J. L., Fanta G.F.: Carbohydr. Polym.7994,

23,275. [42] Chen L., Imam S. H., Gordon S. H., Green R.Y.: l. Enairon. Polym. Degr. 1.997,5,777. [a3] http://wwwmaterbi.itlwelcomeSi.html [44] Coffin D. R., Fish-man M. L.: l. AppL Polym. )ci.7994,54,7377. [45] CoffinD. R., Fishman M. L., Ly T. V.: I. Appl.Polym. 9ci.1996,57,71,.1461Nishio Y., Hratani T., Takahashi T., Manley R. S.

J.: Macromolecules 1989, 22, 2547. I47l Mucha M.,

544 POLIMERY 2002,47, nr 7-8

Piekielna J., Wieczorek A; Macromol. Symp.7999, 144,391. t48l Chiellini E., Cinelli P., Imam S. H.: "BiorelatedPolymers - Sustainable Polymer Science and Technolo-

By" (Eds. Chiellini E., Gil H., Buchert J., Braunegg G.;Van der Zee M.), Gatenholm P. Kluwer Plenum Press.Publ. 2001. [49] Zhang Y., Ghasemzadeh S., Kotliar A.M., Kumar S., Presnell S., Williams L. D.: /. Appl. Polym.Sci. 7999, 7'1., 11.. [50] Chiellini E., Cinelli P., Corti A.,Kenawy E. R., Fernandes E. G., Solaro R.: Mącromol.9ymp.2000,152,83.

[51] Kenawy E. R., Cinelli P., Corti A., Miertus S.,

Chiellini E:. Macromol. Symp.7999,'1.44,351. [52] PCT Int.Appl. WO 2000029460 (2000). [s3] PCT Int. Appl. WO9963007 (1999). t54l PCT Int. Appl. WO 2000011063(2000). [55] Ger. Oft'en.DE 79 972996(2000). [56] PCT Int.Appl. WO 9945067 (1999). [57] PCT Int. Appl. wO 9 946332 (1,999). [58] Iannace S., Nocilla G., Nicolais L.: Eur.Conf. Compos. Mater.: Sci., Technol. Appl.,8th, Volume7,2000,631. [59] PCT Int. Appl. WO 2000011064 (2000).

[60] Braunegg, G., Genser K., Bona R., Haage G., Schel-Iauf F., Winkler E .; Macromol. Symp. 1999, "144,375.

[61] Anderson D. F., Garisto M. A., Bourrut f. C.,Schonbeck M. W., Jave R., Wurzberger A., De Gregorio

R: l, Sustain. Agric. 1995, 7, 39. 162l Shogren R. L.: J . Appl,Polym. Sci.1.999,73,2't59. [63J Shogren R. L.; /. Sustain,Agrił,2000,76,33. t64] u.s. Patent 5 91'9 574 (1'999)' 165lU.S. Patent 5 451 673 (1995). [66J Otaigbe J. U.: 56thAnnu. Tech. Conf. - Soc. Plast. Eng., Yol. 2, 7998, 1.777.

[67] Otaigbe J. U, Goel H., Babcock T., Jane J.: l. Elasto-mers Plast. 1.999, 3'1.,56. t68l Chiellini E., Cinelli P., Fer-nandes E. G., Kenawy E. R., Lazzeri A.: Binmącro-molecules2001.,2,806. [69] Chiellini E., Cinelli P., Corti A.,Kenawy E. R: Polym. Degrad. Stab. 2001.,73, 549. 1701Chiellini E., Cinelli P., Imam S.H., Mao L., Bbmauo-molecules 2007, 2, 7029.

[71] Fanta G. F., Bagley E. B.: "Starch, Graft Copoly-mers", Chapter in: "Encyclopedia of Polymer Scienceand Technology", Suppl .Yol'Ż, Wiley-Interscience, NewYork7977,p.665. [72] Stefanson R. C.: SoiI9ci.7975,119,426. t73) Ross R. J., Sanders f. L.: Bio/EnvironmentallyDegradable Polymer Society,Sth annual meeting, Nash-ville sept. 22, 1.996. [74] Kolomaznik K., Mladek M.,Langmaier F., Janacova D., Taylor M.: |. Am. LeątherChem. Assoc. 2000, 95,55.