Showing papers in "Journal of Polymers and The Environment in 2002"

Sustainable Bio-Composites from Renewable Resources: Opportunities and Challenges in the Green Materials World

Abstract: Sustainability, industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, products, and processes. Biodegradable plastics and bio-based polymer products based on annually renewable agricultural and biomass feedstock can form the basis for a portfolio of sustainable, eco-efficient products that can compete and capture markets currently dominated by products based exclusively on petroleum feedstock. Natural/Biofiber composites (Bio-Composites) are emerging as a viable alternative to glass fiber reinforced composites especially in automotive and building product applications. The combination of biofibers such as kenaf, hemp, flax, jute, henequen, pineapple leaf fiber, and sisal with polymer matrices from both nonrenewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention, i.e., biofiber–matrix interface and novel processing. Natural fiber–reinforced polypropylene composites have attained commercial attraction in automotive industries. Natural fiber—polypropylene or natural fiber—polyester composites are not sufficiently eco-friendly because of the petroleum-based source and the nonbiodegradable nature of the polymer matrix. Using natural fibers with polymers based on renewable resources will allow many environmental issues to be solved. By embedding biofibers with renewable resource–based biopolymers such as cellulosic plastics; polylactides; starch plastics; polyhydroxyalkanoates (bacterial polyesters); and soy-based plastics, the so-called green bio-composites are continuously being developed.

Recent Industrial Applications of Lignin: A Sustainable Alternative to Nonrenewable Materials

Abstract: Lignin represents a vastly under-utilized natural polymer co-generated during papermaking and biomass fractionation. Different types of lignin exist, and these differ with regard to isolation protocol and plant resource (i.e., wood type or agricultural harvesting residue). The incorporation of lignin into polymeric systems has been demonstrated, and this depends on solubility and reactivity characteristics. Several industrial utilization examples are presented for sulfur-free, water-insoluble lignins. These include materials for automotive brakes, wood panel products, biodispersants, polyurethane foams, and epoxy resins for printed circuit boards.

Nanocomposites of Cellulose Acetate Butyrate Reinforced with Cellulose Nanocrystals

Abstract: Nanocrystals were prepared by acid hydrolysis of bacterial cellulose microfibrils. These were topochemically trimethylsilylated, in an attempt to reduce their hydrophilicity. Composites were made by dispersing either native or silylated crystals in cellulose acetatebutyrate matrixes and solution casting of the dispersions. Particles were characterized by transmission electron microscopy. The composites were characterized by differential scanning calorimetry and dynamic mechanical analysis. The unmodified cellulose crystals exhibited better reinforcement characteristics than the trimethylsilated crystals.

Polymer Weathering: Photo-Oxidation

Abstract: As the polymer industry evolved, considerable effort was made to understand the degradation processes of high polymers during weathering and ways were found to inhibit or at least retard their chemical modification and loss of their physical and mechanical properties. Weathering is particularly severe for polymers because it combines the photophysical and photochemical effects of ultraviolet radiation with oxidative and hydrolytic effects of the outdoor environment. This article discusses photo-oxidation degradation (the behavior of polymers as a result of outdoor factors) and mainly concentrates on the photo-oxidative degradation of polyolefins and poly(vinyl) chloride. Polymer photostabilization with ultraviolet screeners, quenchers, hydroperoxide decomposers, and radical scavengers is also described.

Polyols and Polyurethanes from Hydroformylation of Soybean Oil

Abstract: This paper compares physical and mechanical properties of polyurethanes derived via the hydroformylation approach and is a part of our study on the structure–property relationships in polyurethanes created from vegetable oils. The double bonds of soybean oil are first converted to aldehydes through hydroformylation using either rhodium or cobalt as the catalyst. The aldehydes are hydrogenated by Raney nickel to alcohols, forming a triglyceride polyol. The latter is reacted with polymeric MDI to yield the polyurethane. Depending on the degree of conversion, the materials can behave as hard rubbers or rigid plastics. The rhodium-catalyzed reaction afforded a polyol with a 95% conversion, giving rise to a rigid polyurethane, while the cobalt-catalyzed reaction gives a polyol with a 67% conversion, leading to a hard rubber having lower mechanical strengths. Addition of glycerine as a cross-linker systematically improves the properties of the polyurethanes. The polyols are characterized by DSC. The measured properties of polyurethanes include glass transition temperatures, tensile strengths, flexural moduli, and impact strengths.

Effects of Starch Moisture on Properties of Wheat Starch/Poly(Lactic Acid) Blend Containing Methylenediphenyl Diisocyanate

Abstract: Methylenediphenyl diisocyanate was found to improve the interfacial interaction between poly(lactic acid)(PLA) and granular starch. The objective of this research was to study the effect of starch moisture content on the interfacial interaction of an equal-weight blend of wheat starch and PLA containing 0.5% methylenediphenyl diisocyanate by weight. Starch moisture (10% to 20%) had a negative effect on the interfacial binding between starch and PLA. The tensile strength and elongation of the blend both decreased as starch moisture content increased. At 20% moisture level, the starch granules embedded in the PLA matrix were observed to be swollen, resulting in poor strength properties and high water absorption by the blend.

Effect of OH/NCO Molar Ratio on Properties of Soy-Based Polyurethane Networks

Abstract: Polyurethane networks from soybean oil have a number of valuable properties, which are determined by their chemical composition and cross-linking density Changing the molar ratio of reacting groups can vary the latter In this work we have varied the NCO/OH molar ratio (isocyanate index) from 105 to 040 in a soy polyol/MDI system, and tested physical and mechanical properties The degree of swelling in toluene increased from 52–206% by decreasing isocyanate index from 105–04 The sol fractions and network densities determined from swelling in toluene were compared with ones obtained using the network formation theory based on branching processes The comparison of experimental sol fractions and network densities with those predicted by theory of network formation suggest that ∼5–10% of bonds are lost in cycles and that high entanglement contributions increase the network densities Polymers prepared with NCO/OH ratios from 105–08 were glassy while the others were rubbery, and that was reflected in their properties Glass transition temperature (DSC) of the networks decreased from 64–7°C, tensile strength from 47–03 MPa, and elongation at break increased from 7–232% The activation energy of the glass transition, determined from dielectric spectra, varied from 222–156 kJ/mol as the molar ratio of NCO to OH groups decreased from 105–04

Recent Contributions to the Preparation of Polymers Derived from Renewable Resources

Abstract: The aim of this paper is to provide an update on the ongoing research of our laboratory in the field of polymeric materials derived from biomass components. The first section deals with the oxypropylation of different vegetable or animal biomass residues and the use of the ensuing polyols in different polyurethane formulations. Thus, foams, elastomers, and membranes were obtained and their properties compared favorably with those of equivalent materials prepared from petroleum-based sources. The second section is devoted to furan copolymers and their use in reversibly crosslinked elastomers via the Diels–Alder reaction and in the field of photosensitive materials. The third section describes novel approaches to the surface modification of cellulosic fibers to be employed in composite materials with polymeric matrices, consisting in the use of organometallics and siloxanes as coupling agents. The final two sections are devoted to a brief outline of the role of lignins and vegetable oils as additives in printing inks, varnishes, and paints.

Processing and Physical Properties of Plastics Made from Soy Protein Polyester Blends

Abstract: Blending soy protein with polyesters using a polyvinyllactam as a compatibilizer successfully made soy protein-based plastics. The polyesters used to produce blends included polycaprolactone (PCL) and Biomax (a commercial biodegradable polyester). The blends were processed by compounding extrusion and injection molding. Blends containing soy protein/Biomax-poly(vinyl alcohol) had tensile strengths ranging from 16–22 MPa, with samples containing larger percentages of the synthetic polymer exhibiting greater strengths. Blends made from soy protein, Biomax, and PCL had tensile strengths ranging from 27–33 MPa. All the blends had high Young's moduli but demonstrated brittle characteristics as evident from their low elongations at break, ranging from 1.8–3.1%. Plastics made from soy protein/polyester blends exhibited low water absorption and had good stability under ambient conditions relative to the plastics made from soy protein alone. Blends made from soy protein flour produced plastics with the lowest water absorption.

Microwave-Assisted Solvent-Free or Aqueous-Based Synthesis of Biodegradable Polymers

Abstract: Microwave radiation was used as the energy source for various types of chemical derivatizations of polysaccharides and for the synthesis of biodegradable polyesters in solvent-free or aqueous-based reaction systems. A medium to high degree of substitution was obtained for starch acetates, starch succinates, carboxymethyl konjac, aminated starch, and aminated chitosan. Ring-opening polymerization of lactide and e-caprolactone proceeded rapidly even at low power output in the presence of tin octanoate catalyst. Complete monomer conversion and high molecular weight were achieved in less than 6 minutes under nonisothermal conditions. The yield rapidly increased with increasing power output and showed no significant change in a wide range of batch sizes. Polycaprolactone was successfully grafted from starch and konjac acetate in 3 minutes, yielding as high as 24% grafting efficiency and 25% grafting degree.

Novel Polymeric Materials from Biological Oils

Abstract: A variety of novel polymeric materials ranging from elastomers to tough, rigid plastics have been prepared by the cationic copolymerization of regular soybean oil, low-saturation soybean oil, or conjugated low-saturation soybean oil with various alkene commonomers. Using appropriate compositions and reaction conditions, 70–100% of the soybean oil is covalently incorporated into the cross-linked polymer networks, contributing significantly to cross-linking during copolymerization. The resulting thermosets exhibit thermophysical and mechanical properties that are competitive with those of their petroleum-based counterparts. In addition, good damping and shape memory properties have been obtained by controlling the degree of cross-linking and the rigidity of the polymer backbone. New materials with similar characteristics have also been produced from other biological oils, including tung, and fish oils using the same technique. The new, more valuable properties of these bioplastics suggest numerous promising applications of these novel polymeric materials.

Oxygen and Water Barrier Properties of Coated Whey Protein and Chitosan Films

Abstract: Films of whey protein and chitosan acetic acid salt have lower oxygen permeability than, for example, ethylene-co-vinylalcohol under dry conditions, but water and water vapor seriously impair the gas barrier properties. To reduce the oxygen permeability at 90% relative humidity and the water-vapor transmission rate at 100% relative humidity, the films were coated with an alkyd, a beeswax compound, or a nitrocellulose lacquer. Permeability and transmission rate measurements were performed in accordance with standard methods and showed that the beeswax compound and the nitrocellulose were appropriate as water-vapor barriers. Overall migration to water was measured after 10 days exposure time, with the coated surface exposed to the water, showing that the alkyd-coated and the nitrocellulose-coated films were both below the safety limit for food contact. Water absorbency tests, performed by the Cobb method, showed that the films coated with the beeswax compound or with nitrocellulose lacquer exhibit lower absorbency than the alkyd-coated films.

Renewable Resources and Enzymatic Processes to Create Functional Polymers: Adapting Materials and Reactions from Food Processing

Abstract: We are exploiting materials and concepts from food science to create functionalized, environmentally friendly derivatives of the biopolymer chitosan, a byproduct of seafood processing. Functional groups are grafted onto chitosan using tyrosinase, the enzyme responsible for food browning. The functionalizing groups studied include low-molecular-weight phenols derived from natural sources and high-molecular-weight proteins. The approach of using low-molecular-weight phenols to functionalize chitosan is illustrated with arbutin, a natural phenol found in pears. Results demonstrate that tyrosinase initiates reactions that lead to the conversion of arbutin–chitosan solutions into gels. These gels can be rapidly broken by treatment with the chitosan-hydrolyzing enzyme chitosanase, demonstrating that the chitosan derivatives remain biodegradable. We briefly review other studies in which low-molecular-weight natural phenols are enzymatically grafted onto chitosan to confer functional properties. The creation of co-polymers is illustrated by results in which tyrosinase is used to couple gelatin onto chitosan. Gelatin is a proteinaceous byproduct of meat production. The tyrosinase-generated gelatin–chitosan conjugates have been observed to offer interesting rheological and thermal properties. These results demonstrate the potential for using renewable resources and enzymatic processing to create environmentally friendly polymers with useful functional properties.

Biodegradation of Coproducts from Industrially Processed Corn in a Compost Environment 1

Abstract: Information pertaining to biodegradability of renewable polymeric material is critical for the design and development of single-use biodegradable consumer products. The rate and extent of biodegradation of corn fiber, corn zein, cornstarch, distillers grain, and corn gluten meal were evaluated in compost environments under variable temperature, pH, and moisture conditions. Generally, composts with higher temperature (408C), neutral pH (7.0), and 50%‐60% moisture appeared to be ideal for corn coproduct biodegradation, particularly for corn gluten meal and corn zein. Low moisture conditions slowed biodegradation considerably, but degradation rates improved when moisture content increased up to 60%. Thereafter, increased moisture particularly slowed the degradation of corn gluten meal and corn zein, whereas cornstarch degradation remained unaffected. At low pH (4.0) and high pH (11.0) the rate of degradation of most coproducts was slowed somewhat. Cornstarch degradation was slower at pH 7.0, but degradation improved with increased temperatures. Increase in compost temperature from 25 to 408C (in 58C increments) also improved biodegradation of corn fiber and distillers grain. Addition of 1% urea to compost as a nitrogen source decreased the extent of biodegradation nearly 40% for corn gluten meal and corn zein, and 20% for cornstarch samples. Treatment of compost with 0.02% azide inhibited biodegradation of all coproducts, suggesting that the presence of metabolically active microbial cells is required for effective degradation of biobased materials in a compost environment.

Enzyme-Based Vinyl Polymerization

Abstract: In vitro enzyme-mediated polymerization of vinyl monomers is reviewed. Oxidoreductase enzymes have been used for the polymerization of styrene, derivatives of styrene, acrylates, and acrylamide in water and water-miscible co-solvents. Kinetic and mechanistic studies revealed that a ternary system (horseradish peroxidase, H2O2, initiator, or β-diketone) is required for efficient polymerization and the initiator controls the polymer characteristics.

Carbon Molecular Sieving Membranes Derived from Lignin-Based Materials

Abstract: Carbon molecular sieving membranes were prepared by pyrolysis of lignocresol derived from lignin by the phase-separation method. Lignocresol membranes formed by a dip process on a porous α-alumina tubing were carbonized at 400–800°C under nitrogen atmosphere. The thickness of the membrane formed on the outer surface of the substrate was about 400 nm judging from SEM observation. Gas-evolving behavior of lignocresol was measured using thermogravimetry-mass spectrometry (TG-MS). The gaseous products evolved from lignocresol included a number of fragments with higher molecular weights; whereas those from phenolic resin are mainly due to phenol and methylphenol. These evolved pyrolysis fragments effectively contribute to micropore formation of carbonized lignocresol membranes. Gas permeation rates through the membrane decreased in the order of increasing kinetic molecular diameter of the penetrant gas, and the membrane behaved like a “molecular sieve.” The permeation properties were dependent on heating conditions, and a pyrolysis temperature of 600°C gave the best membrane performance. Gas selectivities of the membrane prepared at 600°C were 50, 8, 290, and 87 for CO2/N2, O2/N2, H2/CH4, and CO2/CH4 at 35°C, respectively.

Visualization of the Malleability of the Rubber Core of Rubber Particles from Parthenium argentatum Gray and Other Rubber-Producing Species Under Extremely Cold Temperatures

Abstract: Rubber particles from Parthenium argentatum Gray (guayule) were frozen in liquid nitrogen (−196°C), fractured, and visualized using cryo-scanning electron microscopy. We observed that the rubber polymer core of the rubber particles was still malleable at this extremely cold temperature, and the core stretched substantially during separation of the fracture planes. This malleability was observed in situ in tissue sections, as well as in purified rubber particles, and was found to be independent of purification procedure, guayule line, tissue age, or season. The malleability or stretching phenomenon suggests that P. argentatum rubber has some unique properties because rubber particles from Hevea brasiliensis Mull. Arg. and Ficus elastica Roxb. were brittle at this temperature, fractured cleanly, or showed only tiny threads of material pulling out of the core.

Some Rheological Properties of Latex from Parthenium argentatum Gray Compared with Latex from Hevea brasiliensis and Ficus elastica

Abstract: Latex was purified from Parthenium argentatum Gray (guayule), Hevea brasiliensis Mull. Arg. (the Brazilian or para rubber tree), and Ficus elastica Roxb. (the Indian rubber tree) in ammonium alginate at pH 10. The rheological properties of the different latices (rubber particle suspensions) were determined and compared using flow temperature ramps. Latex from all three species became more viscous with increasing rubber particle concentration and decreasing temperature. At any particular temperature and concentration, latex from F. elastica was by far the most viscous, whereas the H. brasiliensis latex was the least viscous. In addition, the tendency for the latex to coagulate increased with increasing temperature and increasing particle concentration. F. elastica latex was highly sensitive to temperature, H. brasiliensis latex was the least sensitive, and P. argentatum latex demonstrated intermediate properties. The underlying causes of these differences in latex rheology are not clear but may partially relate to the particle size (largest in F. elastica and smallest in H. brasiliensis), the particle size distribution, and/or to the considerable differences in the biochemical components of the monolayer biomembrane that surrounds the various rubber particles. Differences in the molecular weight of the rubber contained within the rubber particles seem less likely to play a role because the particles remain intact in this study.

Earthworms and the Degradation of Lactic Acid–Based Stereocopolymers

Abstract: Two lactic acid–based stereocopolymers, namely 50/50 and 96/4 L/D poly(l-lactic-co-d-lactic acids) and corresponding oligomers, were allowed to age under different conditions in order to investigate their toxicity and that of some potential degradation by-products, namely lactic acid and sodium and calcium lactates, to earthworms. Degradation characteristics in various worm-free and worm-containing media were also investigated under various conditions including direct feeding using impregnated paper or coated tree-leaves, model composting, and vermi composting. Data were compared with abiotic degradation in sterile neutral phosphate buffer. Last but not least, a novel method aimed at assessing the bioassimilation of degradable polymers and oligomers was utilized, which is based on the monitoring of weight changes of a population of starved worms when the worms are given the polymeric or oligomeric compounds as potential nutrients. The work shows that high molar mass poly(lactic acids) can be ingested by earthworms provided they are disintegrated first. However, they cannot be bioassimilated before hydrolytic degradation generates oligomers. The involvement of microorganisms in the bioassimilation is discussed.

Effect of Additives on the Improvement of Mechanical and Degradable Properties of Photografted Jute Yarn with Acrylamide

Abstract: The jute yarn was grafted with acrylamide monomer (AA) under ultraviolet (UV) radiation to modify its mechanical and degradable properties. A number of AA solutions of different concentrations in methanol (MeOH) along with photoinitiator Irgacure 907 [2-methyl-1-(4-methylthiophenyl)-2-morpholinopropanone-1] were prepared. The monomer concentration and irradiation time were optimized. Jute yarn grafted with 30% AA under UV radiation for 60 min showed of the highest polymer loading (PL) value of 22% with a enhanced tensile strength (TS) value of 195% and elongation at break (Eb) value of 256% compared to untreated jute yarn. To further improve the properties of jute yarn, a number of additives (1%) such as urea, polyvinylpyrrolidone, urethane acrylate, and urethane diacrylate were used in the AA (30%) solution. Among all the additives used, urea significantly influenced the PL (27%), TS (230%), and Eb (264%) values of the treated jute yarns. Water uptake and the degradation properties of treated and untreated jute yarn caused by simulated weathering and in soil (25% water) were also studied. The rate of degradation of grafted sample is lower then that of untreated sample. DSC studies showed the thermal stability of the AA plus urea grafted sample.

Degradation of Monophenylheptamethylcyclotetrasiloxane and 2,6- cis -Diphenylhexamethylcycloterasiloxane in Londo Soil

Abstract: The natural degradation of monophenylheptamethylcyclotetrasiloxane and 2,6-cis-diphenylhexamethylcyclotetrasiloxane in soil was evaluated under laboratory conditions. Both monophenyl and 2,6-cis underwent rapid degradation in dry soil generating the same products in varying proportions. During the first 24 hr, approximately 99% of the two materials underwent significant chemical transformations forming silanols of various structures, dimethyl cyclic siloxanes of the structure (Me2SiO)x, and rearrangement products (geometrical isomers) of diphenylhexamethylcyclotetrasiloxane. Among the silanols, the following were identified as trimethylsilyl derivatives: HOSiMe2OH, HOSiMePhOH, HOSiMe2OSiMe2OH, HOSiMePhOSiMe2OH, HOSiMePhOSiMePhOH, HOSiMe2OSiMe2OSiMe2OH, HOSiMePhOSiMe2OSiMe2OH, HOSiMe2OSiMePhOSiMe2OH, HOSiMePhSiMe2OSiMePhOH, HOSiMePhOSiMePhOSiMe2OH, HOSiMePhOSiMe2OSiMe2OSiMe2OH, HOSiMe2OSiMePhOSiMe2OSiMe2OH, HOSiMePhOSiMe2OSiMePhOSiMe2OH, HOSiMePhOSiMePhOSiMe2OSiMe2OH, HOSiMePhOSiMe2OSiMe2OSiMePhOH, HOSiMe2OSiMePh-OSiMePhOSiMe2OH. Derivatization was carried out using bis(trimethylsilyl)trifluoroacetamide. Gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry (atmospheric pressure chemical ionization) analyses were used to derive structures. Structures were confirmed by gas chromatography-mass spectrometry comparisons of synthetic standards. Degradation was slower in wet soil. Nevertheless, in 14 days, the chemical transformation was essentially found to be complete as soil was allowed to dry. Detection of phenol as one of the degradation products revealed the occurrence of carbon–silicon bond cleavage promoted by soil.