Effects of natural polymer acetylation on the anaerobic bioconversion to methane and carbon dioxide

The successful production of novel biodegradable plastic copolymers incorporating both synthetic plastic formulations, such as polystyrene, and naturally occurring biodegradable polymer components, such as cellulose, starch, or xylan, requires stable chemical bonding between these polymers. Modification of the natural polymers through acetylation of the available hydroxyl groups permits the formation of appropriate film-forming plastic copolymers. However, modification of natural polymers has been demonstrated to result in decreased attack by microbial catalysts. For this study, the abundant natural polymers cellulose, starch, and xylan were substituted with acetate to various degrees, and the effect of this modification on the anaerobic biodegradation was assessed using the biochemical methane potential (BMP) protocol. Significant reduction in anaerobic biodegradability resulted with all polymers at substitution levels of between 1.2-1.7. For the xylan acetate series, the trends for anaerobic biodegradation were in good agreement with reduced enzymatic hydyolysis using commercially available xylanase preparations.     

Environmental biodegradation of synthetic polymers I. Test methodologies and procedures

Biodegradation of synthetic polymers is an important property that is used in many applications. Evaluation of the extent of biodegradation has used different methods in recent years. For each environmental compartment, different approaches have to be made in order to obtain valuable data on biodegradability.This review describes validated and accepted methods based on standardized biodegradation tests, analytical tests, enzymatic tests or tests of physical properties to evaluate the biodegradability of synthetic polymers for different types of environmental compartments (e.g., soil, compost or aqueous media).Part II of this review will subsequently report on the environmental biodegradation of different groups of synthetic polymers.     

GRAFT COPOLYMERIZATION OF CELLULOSE,CELLULOSE DERIVATIVES,AND LIGNOCELLULOSE

Abstract

The growth of polymer science has led to the development of new materials in direct competition with natural materials, many of which have been in use since earliest times. This has caused researchers to look more critically at both natural and synthetic macromolecules in order to learn more about their underlying structures and their relation to the properties exhibited by the macromolecules. In this regard, chemical modifications have been devised to impart certain desirable properties of both natural and synthetic macromolecules, and their applications have become an integral part of such chemical modifications. Various chemical modifications (e.g., change of functionality, oxidative degradation, inter- and intramolecular gelation, graft copolymerization), have been practiced to add improved properties to the base polymers. However, among all these methods, modification of polymers via graft copolymerization has been the subject of much interest and has made paramount contribution toward improved industrial and biomedical applications.     

Selection,Characterization, and Biodegradation of Surgical Epoxies

A series of epoxy resins has been formulated on the basis of obtaining low water sorption, low water vapor permeability, retention of electrical properties, and resistance to biodegradation by the body. These resins have been tested for these properties both by accelerated aging in 100°C water and in vivo studies.

A literature survey was conducted on the biodegradation of surgical plastics with the findings that nylon lost 80% of its tensile strength after 3 years implantation while Orlon and Dacron deteriorated considerably less in a 2-year period. Teflon, Mastic, and Mylar showed almost no loss in tensile strength after 17 to 22 months.

The epoxies tested on this program showed no loss in strength after 6 months in vivo.

It appears that materials whose chemical structure contain bonds similar to those found in the body (such as amide groups) are susceptible to biodegradation whereas those such as Teflon which contain only C-C bonds or C-F bonds are not.

Two general types of biodegradation can occur on polymers: Attack starting at the end of a polymer chain and proceeding along the chain to produce monomeric fragments (as in polypropylene), and attack at regular intervals along a polymer chain where susceptible cross-linking groups are present to produce macromolecular fragments.

It has been postulated that attack on polymers takes place in the amorphous areas (if they are present) to leave the more crystalline areas of the material intact. Thus, with implantation, these types of materials become brittle.

Histology on the developed epoxies indicated that epoxies containing nonreactive hydrophobic diluents showed a greater foreign body reaction than normal epoxies without such diluents.     

Biodegradable composite films based on waste gelatin

Gelatin, a naturally occurring polymer, is currently used in various applications comprising manufacturing of pharmaceutical products, x-ray and photographic films development and food processing. However, gelatin scraps generated in the different manufacturing processes may constitute a concern for the environment. Basically speaking, waste disposal deriving from plastics based on synthetic as well as semisynthetic polymeric materials, is becoming an increasingly difficult problem for their unfavorable volume-to-weight ratio and extremely wide variability of type, shape and composition of post consume plastic items that hinder the way to a general unique option for a simple and economically feasible management. As a partial solution to the global issue of plastic waste, in recent years much interest has been devoted to the formulation of environmentally degradable plastic items. Biodegradable mulching films were formulated from blends and composites based on waste gelatin and other natural waste such as sugarcane bagasse or synthetic materials such as PVA. Also, crosslinked films were produced using external or inherent crosslinker. The films were produced either by casting method or spraying on soil surface. The composites were submitted to biodegradation trials. The results showed that the films were biodegradable and the crosslinking could delay and predeterminate their biodegradation rate and extent.     

Polymer Waste Management–Biodegradation,Incineration, and Recycling

Abstract

Increasing volumes of synthetic polymers are manufactured for various applications. The disposal of the used materials is becoming a serious problem. Unlike natural polymers, most synthetic macromolecules cannot be assimilated by microorganisms. Although polymers represent slightly over 10% of total municipal waste, the problem of nonbiodegradability is highlighted by overflowing landfills, polluted marine waters, and unsightly litter. Existing government regulations in Europe and anticipated regulations in the United States will greatly limit the use of polymers in large volume applications (packaging, water treatment, paper and textile sizing, etc.) unless acceptable means of waste management are available. Total management of polymer wastes requires complementary combinations of biodegradation, incineration, and recycling. Biodegradation is the most desirable long-term future solution and requires intensive research and development before it becomes practical. On the other hand, incineration and recycling can become operational in a relatively short time for the improvement of the situation at present and in the near future.     

Macromolecular Architecture-Nature as a Model for Degradable Polymers

Abstract

Nature usually combines polymers with short degradation times with polymers having long degradation times in an energy and material optimized process involving hierarchical systems. Sometimes a natural system of polymers has evolved to degrade in a month, sometimes in many years. The building blocks of the plant and animal kingdom are biopolymers which are either oxidizable or hydrolyzable. In natural composites, combinations of the two are common, e.g., in wood. Current trends in polymer research and marketing of plastics indicate an increasing demand for the development of a diversity of degradable polymer products with a predetermined service-life. We identify four main routes to design degradable polymers. The goal is to tailor-make a material which is more susceptible to environmental degradation factors (e.g., hydrolysis, biodegradation, photooxidation). The most convenient route is to use cheap synthetic bulk polymers and add a biodegradable or photooxidizable component. A more expensive solution is to change the chemical structure by introducing hydrolyzable or oxidizable groups in the repetitive chain of a synthetic polymer. The third route to degradable polymers is to use biopolymers or derivatives of these where the bacterial polyhydroxyalkanoates are perhaps the most studied material of them all. The fourth route is to tailor-make new hydrolyzable structures e.g., polyesters, polyanhydrides, and polycarbonates.     

The Challenge for High Polymers in Medicine,Surgery, and Artificial Internal Organs

High polymers are used in medicine, surgery, or artificial organs in three ways: 1) to construct complete artificial replacements for human organs, 2) to repair, sustain, or augment function of normal organs, and 3) to provide a biochemical function.

Artificial hearts, heart lung machines, and artificial kidneys are examples of artificial organs that man is designing and building to replace natural organs. Plastics are used widely in their construction. Plastics offer a variety of properties needed for these applications, including ease of fabrication, chemical inertness, and nontoxic properties, and a wide range of physical properties in hardness, flexibility, and permeability.

Externally, as adjuncts or assists to natural organs, there are many applications of plastics in present use from clothing to glasses to dentures. Internally, the applications include vascular prostheses, check valve balls for heart valves, encapsulating resins for pacemakers, meshes and foams for reconstructive surgery, drainage tubes, and cannulae for hemodialysis. The plastics most widely used in surgical implants are polytetrafluoroethylene, polypropylene, saturated aromatic polyesters, and polysiloxanes. Growing use is being made of segmented polyurethanes, acrylics, and epoxy resins. Experimental work is under way on polyelectrolytes and various hydrogels based on polyhydroxyl compounds.

The newest class of applications of high polymers is that wherein the polymer has a definite and specific chemical interaction with the biochemistry of the body, i.e., it plays a pharmaceutical role. Examples of this include: 1) synthetic ion exchange resins for absorbing metabolites from the blood; 2) synthetic polyelectrolytes capable of absorbing specific viruses; 3) synthetic polymers such as (a) polyinosinic-polycytidylic acid (a synthetic ribonucleic acid) or (b) a copolymer of vinyl pyran and an undisclosed comonomer which promotes the production of interferon, a chemical substance normally produced by cells as an antiviral agent; and 4) synthetic natural-like polypeptides, enzymes, and chemical modifications of these with enhanced biologic activity.

The future of the use of high polymers in these applications appears to be in the earliest stages. Half a million Americans die each year of heart disease and 60,000 die of kidney disease, hence the potential for artificial versions of these organs is very large. The use of surgical devices is growing steadily. The use of polymers as drugs has not yet been tapped. In 50 years, biochemists will have a battery of synthetic polymer drugs which will cure many diseases, prevent cancer, speed wound healing, and eventually, it is hoped, provide a chemical regime for regeneration of lost limbs and organs.     

Advances in polymer and polymeric nanostructures for protein conjugation

Linear polymers have been considered the best molecular structures for the formation of efficient protein conjugates due to their biological advantages, synthetic convenience and ease of functionalization. In recent years, much attention has been dedicated to develop synthetic strategies that produce the most control over protein conjugation utilizing linear polymers as scaffolds. As a result, different conjugate models, such as semitelechelic, homotelechelic, heterotelechelic and branched or star polymer conjugates, have been obtained that take advantage of these well-controlled synthetic strategies. Development of protein conjugates using nanostructures and the formation of said nanostructures from protein–polymer bioconjugates are other areas in the protein bioconjugation field. Although several polymer–protein technologies have been developed from these discoveries, few review articles have focused on the design and function of these polymers and nanostructures. This review will highlight some recent advances in protein-linear polymer technologies that employ protein covalent conjugation and successful protein-nanostructure bioconjugates (covalent conjugation as well) that have shown great potential for biological applications.     

Modern mass spectrometry in the characterization and degradation of biodegradable polymers

In the last decades, the solid-waste management related to the extensively growing production of plastic materials, in concert with their durability, have stimulated increasing interest in biodegradable polymers. At present, a variety of biodegradable polymers has already been introduced onto the market and can now be competitive with non biodegradable thermoplastics in different fields (packaging, biomedical, textile, etc.). However, a significant economical effort is still directed in tailoring structural properties in order to further broaden the range of applications without impairing biodegradation. Improving the performance of biodegradable materials requires a good characterization of both physico-chemical and mechanical parameters. Polymer analysis can involve many different features including detailed characterization of chemical structures and compositions as well as average molecular mass determination. It is of outstanding importance in troubleshooting of a polymer manufacturing process and for quality control, especially in biomedical applications. This review describes recent trends in the structural characterization of biodegradable materials by modern mass spectrometry (MS). It provides an overview of the analytical tools used to evaluate their degradation. Several successful applications of MALDI-TOF MS (matrix assisted laser desorption ionization time of flight) and ESI MS (electrospray mass spectrometry) for the determination of the structural architecture of biodegradable macromolecules, including their topology, composition, chemical structure of the end groups have been reported. However, MS methodologies have been recently applied to evaluate the biodegradation of polymeric materials. ESI MS represents the most useful technique for characterizing water-soluble polymers possessing different end group structures, with the advantage of being easily interfaced with solution-based separation techniques such as high-performance liquid chromatography (HPLC).     

“Synthetic Metals”: A Novel Role for Organic Polymers (Nobel Lecture)

Since the initial discovery in 1977, that polyacetylene (CH)_x, now commonly known as the prototype conducting polymer, could be p‐ or n‐doped either chemically or electrochemically to the metallic state, the development of the field of conducting polymers has continued to accelerate at an unexpectedly rapid rate and a variety of other conducting polymers and their derivatives have been discovered. Other types of doping are also possible, such as “photo‐doping” and “charge‐injection doping” in which no counter dopant ion is involved. One exciting challenge is the development of low‐cost disposable plastic/paper electronic devices. Conventional inorganic conductors, such as metals, and semiconductors, such as silicon, commonly require multiple etching and lithographic steps in fabricating them for use in electronic devices. The number of processing and etching steps involved limits the minimum price. On the other hand, conducting polymers combine many advantages of plastics, for example, flexibility and processing from solution, with the additional advantage of conductivity in the metallic or semiconducting regimes; however, the lack of simple methods to obtain inexpensive conductive polymer shapes/patterns limit many applications. Herein is described a novel, simple, and cheap method to prepare patterns of conducting polymers by a process which we term, “Line Patterning”.     

光致变色聚合物研究进展

本文主要介绍了9类光致变色聚合物的研究状况,包括光致变色螺吡喃聚合物、螺嗪聚合物、二芳基乙烯光致变色聚合物、偶氮苯类光致变色聚合物、苯氧基萘并萘醌光致变色聚合物、俘精酰亚胺光致变色共聚物、硫靛光致变色共聚物、双硫腙光致变色聚合物以及二氢吲嗪光致变色聚合物等。讨论了聚合物的合成、光致变色性质、影响聚合物性质的因素,并对光致变色聚合物未来的研究重点和方向作了展望。     

Biological–synthetic hybrid block copolymers: Combining the best from two worlds

Although biopolymers and synthetic polymers share many common features, each of these two classes of materials is also characterized by a distinct and very specific set of advantages and disadvantages. Combining biopolymer elements with synthetic polymers into a single macromolecular conjugate is an interesting strategy for synergetically merging the properties of the individual components and overcoming some of their limitations. This article focuses on a special class of biological–synthetic hybrids that are obtained by site‐selective conjugation of a protein or peptide and a synthetic polymer. The first part of the article gives an overview of the different liquid‐phase and solid‐phase techniques that have been developed for the synthesis of well‐defined, that is, site‐selectively conjugated, synthetic polymer–protein hybrids. In the second part, the properties and potential applications of these materials are discussed. The conjugation of biological and synthetic macromolecules allows the modulation of protein binding and recognition properties and is a powerful strategy for mediating the self‐assembly of synthetic polymers. Synthetic polymer–protein hybrids are already used as medicines and show significant promise for bioanalytical applications and bioseparations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1–17, 2005     

Biodegradation of aliphatic and aromatic polycarbonates

Polycarbonate is one of the most widely used engineering plastics because of its superior physical, chemical, and mechanical properties. Understanding the biodegradation of this polymer is of great importance to answer the increasing problems in waste management of this polymer. Aliphatic polycarbonates are known to biodegrade either through the action of pure enzymes or by bacterial whole cells. Very little information is available that deals with the biodegradation of aromatic polycarbonates. Biodegradation is governed by different factors that include polymer characteristics, type of organism, and nature of pretreatment. The polymer characteristics such as its mobility, tacticity, crystallinity, molecular weight, the type of functional groups and substituents present in its structure, and plasticizers or additives added to the polymer all play an important role in its degradation. The carbonate bond in aliphatic polycarbonates is facile and hence this polymer is easily biodegradable. On the other hand, bisphenol A polycarbonate contains benzene rings and quaternary carbon atoms which form bulky and stiff chains that enhance rigidity. Even though this polycarbonate is amorphous in nature because of considerable free volume, it is non-biodegradable since the carbonate bond is inaccessible to enzymes because of the presence of bulky phenyl groups on either side. In order to facilitate the biodegradation of polymers few pretreatment techniques which include photo-oxidation, gamma-irradiation, or use of chemicals have been tested. Addition of biosurfactants to improve the interaction between the polymer and the microorganisms, and blending with natural or synthetic polymers that degrade easily, can also enhance the biodegradation.     

ABSORBABLE SURGICAL SUTURES

Abstract

Sutures are sterile’ filaments used to close wounds and are made of either absorbable or nonabsorbable materials. The choice of suture materials for surgery is made mainly on the basis of biocompatibility and mechanical properties. The biological interaction with the tissues is considered from the point of view of the inflammatory reaction caused. An ideal suture is one that does not merely avoid negative reactions but also keeps a sterile environment and stimulates the process of healing. An absorbable suture is one which is degraded in body tissues to soluble products and disappears from the implant site, usually within 2 to 6 months. A nonabsorbable suture is resistant to biodegradation, becomes encapsulated in a fibrous sheath, and remains in the tissue as a foreign body unless it is surgically removed (e.g., skin sutures) or extruded. Sutures may be fabricated as monofilaments or multifilaments. The latter are generally braided but sometimes twisted or spun and may be coated with wax, silicone, or other polymers to decrease capillarity and improve handling properties. Hoffman [1] presented a survey on the medical applications of synthetic and natural fibrous materials made from such polymers as poly-(fluorocarbons), polyamides, polyolefins, polypeptides, and polysaccharides which are both nonbiodegradable or slowly biodegrad-ing and biodegradable fibers. Frazza [2] prepared a review on mechanical properties and sterilization of natural and synthetic absorbable and nonabsorbable suture materials. The present paper is a review on materials that have been in recent times as absorbable sutures     

Recent progress on cyclic polymers: Synthesis,bioproperties, and biomedical applications

Polymer topologies exert a significant effect on its properties, and polymer nanostructures with advanced architectures, such as cyclic polymers, star‐shaped polymers, and hyperbranched polymers, are a promising class of materials with advantages over conventional linear counterparts. Cyclic polymers, due to the lack of polymer chain ends, have displayed intriguing physical and chemical properties. Such uniqueness has drawn considerable attention over the past decade. The current review focuses on the recent progress in the design and development of cyclic polymer with an emphasis on its synthesis and bio‐related properties and applications. Two primary synthetic strategies towards cyclic polymers, that is, ring‐expansion polymerization and ring‐closure reaction are summarized. The bioproperties and biomedical applications of cyclic polymers are then highlighted. In the end, the future directions of this rapidly developing research field are discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1447–1458     

Injectable and biodegradable hydrogels: gelation, biodegradation and biomedical applications

Injectable hydrogels with biodegradability have in situ formability which in vitro/in vivo allows an effective and homogeneous encapsulation of drugs/cells, and convenient in vivo surgical operation in a minimally invasive way, causing smaller scar size and less pain for patients. Therefore, they have found a variety of biomedical applications, such as drug delivery, cell encapsulation, and tissue engineering. This critical review systematically summarizes the recent progresses on biodegradable and injectable hydrogels fabricated from natural polymers (chitosan, hyaluronic acid, alginates, gelatin, heparin, chondroitin sulfate, etc.) and biodegradable synthetic polymers (polypeptides, polyesters, polyphosphazenes, etc.). The review includes the novel naturally based hydrogels with high potential for biomedical applications developed in the past five years which integrate the excellent biocompatibility of natural polymers/synthetic polypeptides with structural controllability via chemical modification. The gelation and biodegradation which are two key factors to affect the cell fate or drug delivery are highlighted. A brief outlook on the future of injectable and biodegradable hydrogels is also presented (326 references).     

Multi-Layer Pipes for Hydrocarbons Conveyance

The replacement of metals with plastics in piping systems is a well established practice in a vast range of public and industrial applications. However, difficulties still exist, mainly related to the limited chemical resistance of the polymers commonly used in pipe manufacturing to some conveyed fluids. This prevents using plastic pipes in important applications such as the transport of liquid hydrocarbons, particularly in oil fields. The use of chemically resistant polymers, such as fluorinated polyolefins, is precluded by high cost and poor mechanical properties. Co-extrusion of multi-layer pipes carrying an internal chemically resistant liner can be a viable alternative capable to extend the use of plastic pipes to refining and chemical industries. An experimental PE/PA multi-layer pipe has been developed whose resistance to diffusion and mechanical properties have been tested. Tests in real oil fields confirm the good performance of the new pipes.     

Polymers from carbon dioxide: Polycarbonates,polyurethanes

The world polymer industry claims over 2 million tons per year, though most synthetic polymers use petroleum feedstocks, there is a growing effort to prepare polymers from renewable raw materials concerning the depleting fossil fuel resources. In this short review, we would like to emphasize the potential that CO₂ based polymers, polycarbonates and polyurethanes from copolymerization of CO₂ and epoxides, have to mitigate the above concerns, where the newly developed metal catalyst systems allow not only their high efficient synthesis, significant advances have been achieved in stereo-controlled copolymerization. It is also noteworthy that the physical and chemical properties of CO₂ based polymers may be tailored, which help to pave the way from their lab curiosities to practical application, as new applications have been realized such as biodegradable disposal bags, and hydrolysis and oxidation resistant water borne adhesives.     

A review of biodegradation of synthetic plastic and foams

Synthetic polymeric foams have pervaded every aspect of modern life. Although foams provide numerous benefits, they also cause a significant environmental litter problem because of their recalcitrant and xenobiotic nature. Biodegradation may provide solution to the problem, but not enough is known about the biodegradation process of synthetic plastic and plastic-based foams. This review has been written to provide an overview of the current state of plastic foam biodegradation. Several biodegradation pathways of a few select synthetic polymers are also presented along with a discussion on some of the physico-chemical factors that can influence the biodegradation of plastic foams. Department of Chemical and Biochemical Engineering Department of Civil and Environmental Engineering Author to whom all correspondence and reprint requests should be addressed.