Sustainability assessments of bio-based polymers

Bio-based polymers have become feasible alternatives to traditional petroleum-based plastics. However, the factors that influence the sustainability of bio-based polymers are often unclear. This paper reviews published life cycle assessments (LCAs) and commonly used LCA databases that quantify the environmental sustainability of bio-based polymers and summarizes the range of findings reported within the literature. LCA is discussed as a means for quantifying environmental impacts for a product from its cradle, or raw materials extraction, to the grave, or end of life. The results of LCAs from existing databases as well as peer-reviewed literature allow for the comparison of environmental impacts. This review compares standard database results for three bio-based polymers, polylactic acid (PLA), polyhydroxyalkanoate (PHA), and thermoplastic starch (TPS) with five common petroleum derived polymers. The literature showed that biopolymers, coming out of a relatively new industry, exhibit similar impacts compared to petroleum-based plastics. The studies reviewed herein focused mainly on global warming potential (GWP) and fossil resource depletion while largely ignoring other environmental impacts, some of which result in environmental tradeoffs. The studies reviewed also varied greatly in the scope of their assessment. Studies that included the end of life (EOL) reported much higher GWP results than those that limited the scope to resin or granule production. Including EOL in the LCA provides more comprehensive results for biopolymers, but simultaneously introduces greater amounts of uncertainty and variability. Little life-cycle data is available on the impacts of different manners of disposal, thus it will be critical for future sustainability assessments of biopolymers to include accurate end of life impacts.     

Preparation and Characterization of Electroactive Biopolymers

Biopolymers have the potential for use as a matrix for applications such as controlled release devices, environmentally sensitive membranes, mimic materials and energetic applications. Renewable resources (such as starch) can be utilized as polymer matrices for electroactive materials that are sensitive to their environment. Natural polymers are generally more environmentally-friendly and biocompatible than existing synthetic products. Thermoplastic starch is naturally insulative; however, the chemical, electrical, and mechanical properties of the biopolymer matrix can be tailored for specific functionality in a continuous process utilizing reactive extrusion. Conductance can be measured in the solid state by a direct-current resistance method. Ion-conducting materials, produced by doping thermoplastic starch and biopolymers with metal halides, have 5 orders of magnitude greater conductance than native materials. There is a correlation between polymer mobility and conductance. Plant or microbial biopolymers with ionic functional groups have shown promise for higher levels of conductance. The conductance approaches the level of synthetic polymer electrolytes.     

Hydrostatic pressure–dependent wear behavior of thermoplastic polymers in deep sea

It is generally acknowledged that wear behavior of approved water‐lubricated thermoplastic polymers are not susceptible to hydrostatic pressure in seawater environment. However, in our recent study reported in this letter, it has been shown that the wear behavior of thermoplastic polymers sliding in seawater is strongly dependent on the hydrostatic pressure. The correlation between hydrostatic pressure and wear rates of thermoplastic polymers can be expressed in an identical form of exponential function, which has been found to be susceptible to some factors, such as polymer property, seawater absorption, filler type, sliding condition, and counterpart material. Moreover, in this letter, a primary model has been proposed to illuminate the effect of hydrostatic pressure on the wear behavior of thermoplastic polymers sliding in deep sea.     

Synthetic Paper

Synthetic paper can be made either by forming a web from synthetic fibers or by extruding a film from thermoplastic polymers. With suitable starting materials and appropriate treatment it is possible to equal the properties of conventional cellulose paper; in some respects, as in wet strength and dimensional stability, the synthetic papers are clearly superior.     

Membranes based on non-synthetic (natural) polymers for wastewater treatment

During the last decades, rising environmental concerns about the widespread usage of petroleum-based synthetic polymers has caused naturally occurring polymers to gain momentous. As a biocompatible and environmentally friendly alternative, bio-based polymers are continuously gaining new domains of application in drug delivery systems, tissue engineering, membrane technology, bio-sensor devices, etc. There is an increasing number of scientists who have applied various kinds of biopolymers, such as cellulose, chitin, starch, and alginate to fabricate fully or semi-biodegradable membranes for wastewater treatment. Beside biocompatibility, biopolymers combine many attractive features such as hydrophilicity and functionalizability that makes them great candidates to enhance the performance of composite membranes to effectively purify water from hazardous pollutants. On the other hand, elevating thermo-mechanical and chemical stability of these bio-based materials by introducing new organic and inorganic additives is another main focus area. This review is concerned with 1) introducing the promising feature of biopolymers that can be used as a raw material to synthesize membranes for water treatment, 2) proposing a comprehensive categorization of these membranes based on their structure, and 3) discussing the performance of these membranes in eliminating various kinds of contaminants from effluents and their strength and weakness points.     

MICROMOLDING ON CURVED SURFACES WITH THERMOPLASTICS

Microstructures were produced on curved surfaces and micro-protrusions by using direct micromolding with fourthermoplastic polymers. This method is simpler and more convenient than micromolding with liquid prepolymer or using theμTM method. By repeated molding, crossed structures were produced with a stamp prepared only with lines. The processingvariables including the softening temperature of the polymers and heating time were discussed. The result shows that theoptimal molding temperature is preferably slightly higher than the melting temperature of the thermoplastic polymers, atwhich polymers are in the critical states of being melted. This method can be applied to many polymers except those with high softening temperatures or high rate of shrinkage upon temperature change.     

Thermoplastic polymers: overview of several properties and their consequences in flax fibre reinforced composites

In order to assess the most suitable thermoplastic polymer for a certain application, one must know the properties of the available polymers. Since data tend to be widely scattered over many sources, it is the purpose of this article to give an overview of the most relevant properties of a range of thermoplastic polymers. The reported properties are divided into mechanical, physical, and thermal ones. It is clear that many of these properties are interrelated. By consequence some combinations of desired properties are not possible but an overview such as this may provide a useful guide in establishing the best compromise between conflicting property demands. Data are presented mostly as ranges (in tables) as well as in graphs for quick comparison reasons. One specific application (thermoplastic pultrusion with flax as reinforcement) is also studied. In this particular case, polypropylene is found to have the best combination of properties in order to be used as the composite matrix.     

Recent advances in biopolymer based electrospun nanomaterials for drug delivery systems

Drug delivery systems, including liposomes, gels, prodrugs, and so forth, are used to enhance the tissue benefit of a pharmaceutical drug or conventional substance at a specific diseased site with little toxicological impact. Nanotechnology can be a rapidly developing multidisciplinary science that enables the production of polymers at the manometer scale for different medical applications. The use of biopolymers in drug delivery systems provides compatibility, biodegradability and low immunogenicity biologically. Large-scale and smaller-than-expected medication particles can be delivered using biopolymers such as silk fibroins, collagen, gelatine, and others that are easily formed into suspensions. These drug carrier systems are functional at improving drug delivery and can be used in intranasal, transdermal, dental, and ocular delivery systems. This study discusses the latest developments in drug delivery methods based on nanomaterials, mainly using biopolymers like proteins and polysaccharides.     

Shape memory ionomers

This review is focused on the use of ionomers in shape memory polymers. Ionomers are polymers that contain less than ∼15% ionic groups. The incompatibility between the ion-pairs and the polymer backbone drives microphase separation producing dispersed ionic aggregates, which can physically crosslink the polymer. Shape memory polymers are responsive materials that can be deformed to program a temporary shape and then recovered on application of an external stimulus. Through the review of the main types of ionomers used in shape memory polymers, polyurethanes and polyester ionomers, polyolefin and polyaromatic ionomers, and perfluorosulfonic acid ionomers (i.e., Nafion^®) it will be shown that ionomers can produce robust thermoplastic shape memory polymers and in many cases impart unique properties which allow advanced shape memory materials to be obtained including antibacterial, high temperature, and multishape memory polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1389–1396     

Cellulose Nanocomposites

Cellulose is a linear polysaccharide and one of the world's most abundant biopolymers. It is one of the renewable biopolymers being studied to reduce the dependence on non-renewable mineral oil based products. Cellulose can be used in different kinds of composites, including the recent nanocomposites.The production of nanoscale cellulose fibers and their use in polymer composites gained increasing attention due to their interesting properties and potential applications. This review paper is trying to cover studies done to use various forms of cellulose as reinforcement for different polymers, as matrix, as reinforcement and matrix for the same nanocomposite and as a component in polyblend nanocomposites beside other polymers.     

Biopolymers for surface engineering of paper-based products

The combination of biopolymer science and technology with surface engineering of paper-based cellulosic materials has a lot of potential in stepping forward to a sustainable future. Various biopolymers such as oxidized starch, carboxymethyl cellulose, and polylatic acid have been commercially used to engineer paper surface. The paper-based cellulosic products are widely used for printing/writing and packaging applications. However, the production of these products are currently dependent mainly upon the use of petroleum-based materials including synthetic pigment coating latexes and barrier coating materials. The major challenges associated with some biopolymers are their relatively high costs and unsatisfactory performances. Continuing efforts are being made to enable the increased and value-added use of various biopolymers in paper surface engineering. These polymers can be based on cellulose, hemicelluloses, chitosan, alginate, protein, polylactic acid, and polyhydroxyalkanoate. The biopolymer-engineered paper products can be tailored for use as substitutes for various non-renewable materials including plastics and metals as well. Future development in the area of biopolymers for paper surface engineering is likely to lead to new possibilities and breakthroughs, paving the way for a substantially sustainable and green future.     

Precision Biopolymers from Protein Precursors for Biomedical Applications

The synthesis of biohybrid materials with tailored functional properties represents a topic of emerging interest. Combining proteins as natural, macromolecular building blocks, and synthetic polymers opens access to giant brush‐like biopolymers of high structural definition. The properties of these precision polypeptide copolymers can be tailored through various chemical modifications along their polypeptide backbone, which expands the repertoire of known protein‐based materials to address biomedical applications. In this article, the synthetic strategies for the design of precision biopolymers from proteins through amino acid specific conjugation reagents are highlighted and the different functionalization strategies, their characterization, and applications are discussed.     

Biopolymers as a Flexible Resource for Nanochemistry

Biomass is an abundant source of chemically diverse macromolecules, including polysaccharides, polypeptides, and polyaromatics. Many of these biological polymers (biopolymers) are highly evolved for specific functions through optimized chain length, functionalization, and monomer sequence. As biopolymers are a chemical resource, much current effort is focused on the breakdown of these molecules into fuels or platform chemicals. However there is growing interest in using biopolymers directly to create functional materials. This Minireview uses recent examples to show how biopolymers are providing new directions in the synthesis of nanostructured materials.     

Thermoplastic starch blends: A review of recent works

The aim of this review is to discuss the recent developments in thermoplastic starch blends. Starch has been considered as an excellent candidate to partially substitute synthetic polymer in packaging, agricultural mulch and other low-cost applications. Recently, the starch granules were plasticized using different plasticizers under heating and shearing, giving rise to a continues phase in the form of a viscous melt which can be processed using traditional plastic processing techniques, such as injection molding and extrusion. This kind of starch composites is called thermoplastic starch. Unfortunately, thermoplastic starch presents some drawbacks, such as low degradation temperatures, which make it difficult to process, poor mechanical properties and high water susceptibility. Much work has been carried out to overcome these drawbacks, including the combination of thermoplastic starch with other polymers, aiming at lowering the cost and enhancing the biodegradability of the final product.     

General Model of Temperature-dependent Modulus and Yield Strength of Thermoplastic Polymers

A general model was developed to predict the temperature-dependent modulus and yield strength of different thermoplastic polymers.This model,which depends on only two parameters with clear and specific physical meanings,can describe the temperaturedependent modulus and yield strength of thermoplastic polymers over the full glass transition region.The temperature-dependent modulus and yield strength of three thermoplastic polymers were measured by uniaxial tension tests over a temperature range of 243-383 K.The predictions showed excellent agreement with the experimental data.Sensitivity analysis of model input parameters showed negligible effect on the present general model.The universality of the present general model was further validated,showing excellent agreement with published experimental data on other thermoplastic polymers and their composites.     

Synergistic effect of graphene oxide nanoplatelets and cellulose nanofibers on mechanical,thermal, and barrier properties of thermoplastic starch

In recent years, because of the limited availability of oil resources and the increasing concerns regarding environment protection, much attention has been drawn to produce packaging films based on degradable biopolymers instead of synthetic polymers. On the other hand, because of the high costs of oil extraction, raw materials and film production, and disposing of the waste products of synthetic films, the need to replace these films with less pollutant and more cost‐effective films is growing globally. In this study, to answer the need for replacing synthetic polymer films, nanocomposite films based on thermoplastic starch reinforced with cellulose nanofibers and graphene oxide nanoplatelets were produced and characterized. The results implied that the synergistic effect of cellulose nanofibers and graphene oxide nanoplatelets has played an important role in improving the mechanical properties of the films. The results showed that with the addition of cellulose nanofibers and graphene oxide nanoplatelets, the tensile strength and elastic modulus of starch film were increased from 3 and 32 MPa to 13 and 436 MPa, which corresponds to 438% and 1435% improvement, respectively. In addition, the oxygen permeability resistance and the water vapor transmission for samples containing 3 wt% of graphene oxide nanoplatelets was decreased by 78% and 30% compared with the thermoplastic starch film, respectively. The permeability coefficient of the samples containing 3 wt% graphene oxide nanoplatelets for oxygen, nitrogen, and carbon dioxide have proved to be 0.051, 0.054, and 0.047 barrer, which shows that these films can perform well as packaging films.     

The quantitative description of small molecule binding to abiotic polymers

The variation of equilibrium constants for the binding of small molecules to abiotic polymers as a function of structure is quantitatively described by the intermolecular force (IMF) equation and relationships derived from it. Structural variations in both the small molecules and in the polymers were studied. The data were taken from the literature. The results obtained suggest that the IMF equation may be generally useful for modelling the effect of structural variation on polymer properties which depend on the difference in intermolecular forces between initial and final states. They also provide a model for nonspecific binding to biopolymers.     

A general concept for the preparation of hierarchically structured pi-conjugated polymers

Typical biopolymers exhibit structures and order on different length scales. By contrast, the number of synthetic polymers with a similar degree of hierarchical structure formation is still limited. Starting from recent investigations on the structures of amyloid proteins as well as research activities toward nanoscopic scaffolds from synthetic oligopeptides and their polymer conjugates, a general strategy toward hierarchically structured pi-conjugated polymers can be developed. The approach relies on the supramolecular self-assembly of diacetylene macromonomers based on beta-sheet forming oligopeptides equipped with hydrophobic polymer segments. Polymerization of these macromonomers proceeds under retention of the previously assembled hierarchical structure and yields pi-conjugated polymers with multi-stranded, multiple-helical quaternary structures.     

6. Prospects for future applications of cellulose acetate

The prospects for future applications of cellulose acetate (CA) and cellulose esters (CE) were assessed via an analysis of literature data. An examination of more than 50,000 citations in the published literature with relevance to CA and CE has shown that, while the R&D effort continues without discernible slow-down, the emphasis has shifted in favor of D at the expense of R in recent years; more publications now originate in Southeast Asian countries; and most current journal articles deal with specialty products, such as membranes, controlled release agents, and biopolymers. The prospects for future applications are viewed as being related to the ability to add new performance features to CA, particularly thermal processability, water-dispersibility, and the ability to interact with other polymers on the molecular level. This can be achieved by such secondary modifications as the introduction of plasticizing (mixed) ester substituents, carboxyl groups, and the use of (monofunctional) oligomers in block copolymers, respectively. In addition, the adoption of acetylation technology to lower grade pulps and even wood and wood fibers may result in new business opportunities in thermoplastic and soluble wood esters, or in acetylated solid wood products with superior dimensional, biological and light-stability characteristics.     

Visualization of the morphology at the interphase of glass fibre reinforced epoxy-thermoplastic polymer composites

This work deals with the effect that the use of glass fibres has on the morphology developed by a thermoplastic polymer modified epoxy. In particular, three surface modifications of the glass fibres were studied: calcinations desizing, activation with hydrochloric acid and coating with 3-aminopropyltriethoxy silane. As the epoxy polymer, a model system based on the full reaction of DGEBA and 2-methyl-1,5-diaminopentane was used. As the modifiers of the epoxy thermoset, two thermoplastic polymers were used: poly(methylmethacrylate) and polystyrene. The morphologies were examined either in the polymer bulk or at the interfaces by means of scanning electron microscopy and atomic force microscopy. After a thoroughly examination of the samples it was found that the thermoplastic polymers preferentially accumulate at the interfaces of these materials when activated and silanized glass fibres are used. These results might be attributed to a gradual phase separation process due to stoichiometric gradients which, on the other hand, seems to be conditioned by the nature of glass fibres surface.