Lifetime prediction of biodegradable polymers

Crystalline Characteristics, Mechanical Properties, Thermal Degradation Kinetics and Hydration Behavior of Biodegradable Fibers Melt-Spun from Polyoxymethylene/Poly(l-lactic acid) Blends

A series of polyoxymethylene (POM)/poly(l-lactic acid) (PLLA) blends were prepared by melt extrusion, and their spinnability was confirmed by rheological characterizations, successive self-nucleation, and annealing thermal fractionation analysis. The bicomponent fibers were prepared by means of the melt-spinning and post-drawing technologies using the above-obtained blends, and their morphology, crystalline orientation characteristics, mechanical performance, hydration behavior, and thermal degradation kinetics were studied extensively. The bicomponent fibers exhibited a uniform diameter distribution and compact texture at the ultimate draw ratio. Although the presence of PLLA reduced the crystallinity of the POM domain in the bicomponent fibers, the post-drawing process promoted the crystalline orientation of lamellar folded-chain crystallites due to the stress-induced crystallization effect and enhanced the crystallinity of the POM domain accordingly. As a result, the bicomponent fibers achieved the relatively high tensile strength of 791 MPa. The bicomponent fibers exhibited a partial hydration capability in both acid and alkali media and therefore could meet the requirement for serving as a type of biodegradable fibers. The introduction of PLLA slightly reduced the thermo-oxidative aging property and thermal stability of the bicomponent fibers. Such a combination of two polymers shortened the thermal lifetime of the bicomponent fibers, which could facilitate their natural degradation for ecological and sustainable applications.

Predicting degradation rate of genipin cross-linked gelatin scaffolds with machine learning

Genipin can improve weak mechanical properties and control high degradation rate of gelatin, as a cross-linker of gelatin which is widely used in tissue engineering. In this study, genipin cross-linked gelatin biodegradable porous scaffolds with different weight percentages of gelatin and genipin were prepared for tissue regeneration and measurement of their various properties including morphological characteristics, mechanical properties, swelling, degree of crosslinking and degradation rate. Results indicated that the sample containing the highest amount of gelatin and genipin had the highest degree of crosslinking and increasing the percentage of genipin from 0.125% to 0.5% enhances ultimate tensile strength (UTS) up to 113% and 92%, for samples with 2.5% and 10% gelatin, respectively. For these samples, increasing the percentage of genipin, reduce their degradation rate significantly with an average value of 124%. Furthermore, experimental data are used to develop a machine learning model, which compares artificial neural networks (ANN) and kernel ridge regression (KRR) to predict degradation rate of genipin-cross-linked gelatin scaffolds as a property of interest. The predicted degradation rate demonstrates that the ANN, with mean squared error (MSE) of 2.68%, outperforms the KRR with MSE = 4.78% in terms of accuracy. These results suggest that machine learning models offer an excellent prediction accuracy to estimate the degradation rate which will significantly help reducing experimental costs needed to carry out scaffold design.

An experimental and theoretical study of the erosion of semi-crystalline polymers and the subsequent generation of microparticles

The increase of plastics and microplastics in the environment is a major environmental challenge. Still, little is known about the degradation kinetics of macroplastics into smaller particles, under the joint actions of micro-organisms and physico-chemical factors, like UV or mechanical constraints. In order to gain insight into (bio)-degradation in various media, we perform accelerated erosion experiments by using a well-known enzymatic system. We show that the microstructure of semi-crystalline polymers plays a crucial role in the pattern formation at their surface. For the first time, the release of fragments of micrometric size is evidenced, through a mechanism that does not involve fracture propagation. A geometric erosion model allows a quantitative understanding of erosion rates and surface patterns, and provides a critical heterogeneity size, parting two types of behavior: spherulites either released, or eroded in situ. This new geometric approach could constitute a useful tool to predict the erosion kinetics and micro-particle generation in various media.

Mainstream Ammonium Recovery to Advance Sustainable Urban Wastewater Management

Throughout the 20th century, the prevailing approach toward nitrogen management in municipal wastewater treatment was to remove ammonium by transforming it into dinitrogen (N₂) using biological processes such as conventional activated sludge. While this has been a very successful strategy for safeguarding human health and protecting aquatic ecosystems, the conversion of ammonium into its elemental form is incompatible with the developing circular economy of the 21st century. Equally important, the activated sludge process and other emerging ammonium removal pathways have several environmental and technological limitations. Here, we assess that the theoretical energy embedded in ammonium in domestic wastewater represents roughly 38-48% of the embedded chemical energy available in the whole of the discharged bodily waste. The current routes for ammonium removal not only neglect the energy embedded in ammonium, but they can also produce N₂O, a very strong greenhouse gas, with such emissions comprising the equivalent of 14-26% of the overall carbon footprint of wastewater treatment plants. N₂O emissions often exceed the carbon emissions related to the electricity consumption for the process requirements of WWTPs. Considering these limitations, there is a need to develop alternative ammonium management approaches that center around recovery of ammonium from domestic wastewater rather than deal with its "destruction" into elemental dinitrogen. Current ammonium recovery techniques are applicable only at orders of magnitude above domestic wastewater strength, and so new techniques based on physicochemical adsorption are of particular interest. A new pathway is proposed that allows for mainstream ammonium recovery from wastewater based on physicochemical adsorption through development of polymer-based adsorbents. Provided adequate adsorbents corresponding to characteristics outlined in this paper are designed and brought to industrial production, this adsorption-based approach opens perspectives for mainstream continuous adsorption coupled with side-stream recovery of ammonium with minimal chemical requirements. This proposed pathway can bring forward an effective resource-oriented approach to upgrade the fate of ammonium in urban water management without generating hidden externalized environmental costs.

Microbial degradation of four biodegradable polymers in soil and compost demonstrating polycaprolactone as an ideal compostable plastic

Plastics are an indispensable material but also a major environmental pollutant. In contrast, biodegradable polymers have the potential to be compostable. The biodegradation of four polymers as discs, polycaprolactone (PCL), polyhydroxybutyrate (PHB), polylactic acid (PLA) and poly(1,4 butylene) succinate (PBS) was compared in soil and compost over a period of more than 10 months at 25 °C, 37 °C and 50 °C. Degradation rates varied between the polymers and incubation temperatures but PCL showed the fastest degradation rate under all conditions and was completely degraded when buried in compost and incubated at 50 °C after 91 days. Furthermore, PCL strips showed a significant reduction in tensile strength in just 2 weeks when incubated in compost >45 °C. Various fungal strains growing on the polymer surfaces were identified by sequence analysis. Aspergillus fumigatus was most commonly found at 25 °C and 37 °C, while Thermomyces lanuginosus, which was abundant at 50 °C, was associated with PCL degradation.

Degradation of Polymer Films on Surfaces: A Model Study with Poly(sebacic anhydride)

There is compelling evidence that the degradation kinetics of thin polymer films differ significantly from those of bulk materials, as interfacial effects become dominant. Therefore, it is crucial to investigate these kinetics separately. Qualitative analytics of thin film degradation exist, e.g. by scanning electron microscopy or atomic force microscopy (AFM), but a quantitative study is so far missing. In this work, poly(sebacic anhydride) (PSA), an aliphatic polyanhydride, is used as a model system for a quantitative degradation study. PSA was spin-coated onto silicon or gold substrates. The degradation of these PSA films was monitored by ellipsometry, surface-plasmon resonance spectroscopy (SPR), and Fourier transform infrared spectroscopy (FTIR). Two kinetic regimes were observed when plotting the relative layer thickness determined by FTIR and SPR against the degradation time. The data obtained by FTIR showed a single process for the rate of ester bond cleavage. Overall, the degradation rate constants of PSA determined by the different methods were consistent. The degradation rate constants of PSA film up to 378 nm thickness were constant. Several thicker free-standing samples studied gravimetrically had a degradation rate constant that was one order of magnitude slower, thus confirming thickness-dependent degradation rate constants.

Species-Specific Biodegradation of Sporopollenin-Based Microcapsules

Sporoderms, the outer layers of plant spores and pollen grains, are some of the most robust biomaterials in nature. In order to evaluate the potential of sporoderms in biomedical applications, we studied the biodegradation in simulated gastrointestinal fluid of sporoderm microcapsules (SDMCs) derived from four different plant species: lycopodium (Lycopodium clavatum L.), camellia (Camellia sinensis L.), cattail (Typha angustifolia L.), and dandelion (Taraxacum officinale L.). Dynamic image particle analysis (DIPA) and field-emission scanning electron microscopy (FE-SEM) were used to investigate the morphological characteristics of the capsules, and Fourier-transform infrared (FTIR) spectroscopy was used to evaluate their chemical properties. We found that SDMCs undergo bulk degradation in a species-dependent manner, with camellia SDMCs undergoing the most extensive degradation, and dandelion and lycopodium SDMCs being the most robust.

Degradation of brominated polymeric flame retardants and effects of generated decomposition products

Brominated flame retardants are often associated with adverse environmental effects. Nevertheless, these chemicals are required in order to comply with fire safety standards. Therefore, a better environmental profile is desirable. A "new" class of flame retardants is claimed to fulfil this request while still being feasible for established industrial processes. Different to previous brominated flame retardants, this new group is based on a polymeric structure that could indeed lead to a better environmental profile. However, not much is known about the long-term behaviour of such flame retardants. This short review summarizes what has already been published. With an annual production volume of 26,000 metric tons, "Polymeric FR" is currently the only industrially produced representative of this group. It has been shown to degrade under specific circumstances (following UV and heat exposure). Detected degradation products cause almost no acute toxicity, whereas chronic toxicity might be relevant. Nevertheless, as long as polymeric flame retardants are only used in building insulation, the actual risk seems to be rather limited.

Degradability of chitosan micro/nanoparticles for pulmonary drug delivery

Chitosan, a natural carbohydrate polymer, has long been investigated for drug delivery and medical applications due to its biodegradability, biocompatibility and low toxicity. The micro/nanoparticulate forms of chitosan are reported to enhance the efficiency of drug delivery with better physicochemical properties including improved solubility and bioavailability. This polymer is known to be biodegradable and biocompatible; however, crosslinked chitosan particles may not be biodegradable. Crosslinkers (e.g., tripolyphosphate and glutaraldehyde) are needed for efficient micro/nanoparticle formation, but it is not clear whether the resultant particles are biodegradable or able to release the encapsulated drug fully. To date, no studies have conclusively demonstrated the complete biodegradation or elimination of chitosan nanoparticles in vivo. Herein we review the synthesis and degradation mechanisms of chitosan micro/nanoparticles frequently used in drug delivery especially in pulmonary drug delivery to understand whether these nanoparticles are biodegradable.

The rate of biodegradation of PHA bioplastics in the marine environment: A meta-study

There is a reasonably extensive body of literature recording mass loss of polyhydroxyalkanoates (PHAs) (a class of biodegradable plastics) in the natural marine environment. However, to date, this research has been very disparate. Thus, it remains unclear what the timeframe for the biodegradation of such marine biodegradable plastics actually is. The aim of this work was to determine the rate of biodegradation of PHA in the marine environment and apply this to the lifetime estimation of PHA products. This provides the clarification required as to what 'marine biodegradation of PHA' means in practicality and allows the risks and benefits of using PHA to be transparently discussed. It was determined that the mean rate of biodegradation of PHA in the marine environment is 0.04-0.09 mg·day^-1·cm^-2 (p = 0.05) and that, for example, a PHA water bottle could be expected to take between 1.5 and 3.5 years to completely biodegrade.

3D-Printed Biodegradable Microswimmer for Theranostic Cargo Delivery and Release

Untethered mobile microrobots have the potential to leverage minimally invasive theranostic functions precisely and efficiently in hard-to-reach, confined, and delicate inner body sites. However, such a complex task requires an integrated design and engineering, where powering, control, environmental sensing, medical functionality, and biodegradability need to be considered altogether. The present study reports a hydrogel-based, magnetically powered and controlled, enzymatically degradable microswimmer, which is responsive to the pathological markers in its microenvironment for theranostic cargo delivery and release tasks. We design a double-helical architecture enabling volumetric cargo loading and swimming capabilities under rotational magnetic fields and a 3D-printed optimized 3D microswimmer (length = 20 μm and diameter = 6 μm) using two-photon polymerization from a magnetic precursor suspension composed from gelatin methacryloyl and biofunctionalized superparamagnetic iron oxide nanoparticles. At normal physiological concentrations, we show that matrix metalloproteinase-2 (MMP-2) enzyme could entirely degrade the microswimmer in 118 h to solubilized nontoxic products. The microswimmer rapidly responds to the pathological concentrations of MMP-2 by swelling and thereby boosting the release of the embedded cargo molecules. In addition to delivery of the drug type of therapeutic cargo molecules completely to the given microenvironment after full degradation, microswimmers can also release other functional cargos. As an example demonstration, anti-ErbB 2 antibody-tagged magnetic nanoparticles are released from the fully degraded microswimmers for targeted labeling of SKBR3 breast cancer cells in vitro toward a potential future scenario of medical imaging of remaining cancer tissue sites after a microswimmer-based therapeutic delivery operation.

Biocompatibility of Resorbable Polymers: A Historical Perspective and Framework for the Future

The history of resorbable polymers containing glycolide, lactide, ε-caprolactone and trimethylene carbonate, with a special emphasis being placed on the time frame of the 1960s-1990s is described. Reviewing the history is valuable when looking into the future perspectives regarding how and where these monomers should be used. This story includes scientific evaluations indicating that these polymers are safe to use in medical devices, while the design of the medical device is not considered in this report. In particular, we present the data regarding the tissue response to implanted polymers, as well as the toxicity and pharmacokinetics of their degradation products. In the translation of these polymers from "the bench to the bedside," various challenges have been faced by surgeons, medical doctors, biologists, material engineers and polymer chemists. This Perspective highlights the visionary role played by the pioneers, addressing the problems that occurred on a case by case basis in translational medicine.

Commercial plastics claiming biodegradable status: Is this also accurate for marine environments?

Concerns about plastic pollution and global public policies have encouraged consumers to acquire environmentally friendly products. Thus, products made of biodegradable plastics have been preferred by the public, despite their costs. However, greenwashing practices, promising more environmental benefits than the products actually offer, has become frequent. Nevertheless, no studies assessing the occurrence of greenwashing in commercial plastic products sold in large world economies have been performed. The present study aimed to experimentally evaluate alterations in structure and chemical composition of selected plastic products marketed in Canada, USA and Brazil. The aging experiments carried out by seawater immersion for 180 days showed no evidence of degradation in 4 out of the 6 studied samples, despite product claims of biodegradability or 100% degradability status. This finding denotes unequivocal greenwashing practices, even including bags made of polyethylene, an ordinary non-biodegradable polymer. Thus, the inadequate adoption of green marketing is deceiving to consumers and may lead to improper disposal of these materials. These practices are highly counterproductive in view of the global public policies recently adopted to control plastic pollution. Therefore, considering the technologies currently available for identification of polymers, a strict control should be exercised over products that claim biodegradable status.

Understanding the Mobilization of a Nitrification Inhibitor from Novel Slow Release Pellets, Fabricated through Extrusion Processing with PHBV Biopolymer

Dicyandiamide (DCD) has been studied as a stabilizer for nitrogen fertilizers for over 50 years. Its efficacy is limited at elevated temperatures, but this could be addressed by encapsulation to delay exposure. Here, poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) was investigated as a biodegradable matrix for the encapsulation of DCD. Cylindrical ∼3 mm × 3 mm pellets were fabricated through extrusion processing with 23 wt % DCD. Release kinetics were monitored in water, sand, and both active and γ-irradiated agricultural clay loam soils. Raman maps showed a wide particle size distribution of DCD crystals and indicated that Hitachi's classic moving front theory did not hold for this formulation. The inhibitor release kinetics were mediated by four distinct mechanisms: (i) initial rapid dissolution of surface DCD, (ii) channeling of water through voids and pores in the PHBV matrix, (iii) gradual diffusion of water and DCD through layers of PHBV, and (iv) biodegradation of the PHBV matrix. After ∼6 months, 45-100% release occurred, depending on the release media. PHBV is shown to be an effective, biodegradable matrix for the long-term slow release of nitrification inhibitors.

Human blood plasma catalyses the degradation of Lycopodium plant sporoderm microcapsules

Plant sporoderm are among the most robust biomaterials in nature. We investigate the erosion of Lycopodium sporoderm microcapsules (SDMCs) triggered by human blood plasma. Dynamic image particle analysis (DIPA), field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FTIR) spectroscopy demonstrate the degradation events, suggesting bulk erosion as the dominant mechanism for SDMCs fragmentation in human blood. These results should prove valuable in discerning the behaviour of SDMCs in potential biological applications.

Nanocellulose-assisted construction of hydrophilic 3D hierarchical stereocomplex meshworks in enantiomeric polylactides: towards thermotolerant biocomposites with enhanced environmental degradation

A hydrophilic and hierarchical 3D stereocomplexed crystalline meshwork was in situ constructed in fully bio-derived enantiomeric polylactide/cellulose nanocrystal nanocomposites.

The High Density Polyethylene Composite with Recycled Radiation Cross-Linked Filler of rHDPEx

This article discusses the possibilities of using radiation cross-linked high density polyethylene (HDPEx) acting as a filler in the original high density polyethylene (HDPE) matrix. The newly created composite is one of the possible answers to questions relating to the processing of radiation cross-linked thermoplastics. Radiation cross-linked networking is-nowadays, a commonly used technology that can significantly modify the properties of many types of thermoplastics. This paper describes the influence of the concentration of filler, in the form of grit or powder obtained by the grinding/milling of products/industrial waste from radiation cross-linked high density polyethylene (rHDPEx) on the mechanical and processing properties and the composite structure. It was determined that, by varying the concentration of the filler, it is possible to influence the mechanical behaviour of the composite. The mechanical properties of the new composite-measured at room temperature, are generally comparable or better than the same properties of the original thermoplastic. This creates very good assumptions for the effective and economically acceptable, processing of high density polyethylene (rHDPEx) waste. Its processability however, is limited; it can be processed by injection moulding up to 60 wt %.

Langmuir Monolayers as Tools to Study Biodegradable Polymer Implant Materials

Langmuir monolayers provide a fast and elegant route to analyze the degradation behavior of biodegradable polymer materials. In contrast to bulk materials, diffusive transport of reactants and reaction products in the (partially degraded) material can be neglected at the air-water interface, allowing for the study of molecular degradation kinetics in experiments taking less than a day and in some cases just a few minutes, in contrast to experiments with bulk materials that can take years. Several aspects of the biodegradation behavior of polymer materials, such as the interaction with biomolecules and degradation products, are directly observable. Expanding the technique with surface-sensitive instrumental techniques enables evaluating the evolution of the morphology, chemical composition, and the mechanical properties of the degrading material in situ. The potential of the Langmuir monolayer degradation technique as a predictive tool for implant degradation when combined with computational methods is outlined, and related open questions and strategies to overcome these challenges are pointed out.

In vitro degradation of a unique porous PHBV scaffold manufactured using selective laser sintering

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds have shown great promise for bone tissue engineering applications. The investigation of their hydrolytic degradation is thus essential to understand the effect of hydrolysis on the complex biodegradation behavior of PHBV scaffolds. In this study, we investigated the degradation behavior of high molecular weight PHBV scaffolds manufactured using selective laser sintering (SLS) without using predesigned porous architectures. The manufactured scaffolds have high specific surface areas with great water-uptake abilities. After an incubation of 6 weeks in phosphate-buffered saline solution, the structural integrity of the scaffolds was unaffected. However, a significant decrease in molecular weight ranging from 39% to 46% was found. The measured weight loss was negligible, but their compressive modulus and strength both decreased, likely due to water plasticization. These findings suggest that hydrolytic degradation of PHBV by means of bulk degradation was the predominant mechanism, attributed to their excellent water absorptivity. Overall, the PHBV scaffolds manufactured using SLS exhibited adequate mechanical properties and satisfactory structural integrity after incubation. As a result, the scaffolds have great potential as candidates for bone repair in clinical practice. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 154-162, 2019.

Challenges for the development of surface modified biodegradable polyester biomaterials: A chemistry perspective

The design of current implants produced from biodegradable polyesters is based on strength and rate of degradation and tailored by the choice of polyester used. However, detailed knowledge about the degradation mechanism of surface modified materials with applications in biomaterials science and tissue engineering is currently lacking. This perspective aims to outline the need for a greater focus on analyzing the degradation of modified polyesters to ensure they can fulfil their intended function and that degradation products can effectively be cleared from the body. The status of the literature regarding surface modified polyesters is summarized to illustrate the main aspects investigated in recent studies and specifically the number of studies investigating the fate of the materials upon degradation.

Non-destructive analysis of polymers and polymer-based materials by compact NMR

Low-field nuclear magnetic resonance (NMR) based on permanent magnet technologies is currently experiencing a considerable growth of popularity in studying polymer materials. Various bulk properties can be probed with compact NMR tabletop instruments by placing the sample of interest inside the magnet. Contrary to this, compact NMR sensors with open geometries give access to depth-dependent properties of polymer samples and objects of different sizes and shapes truly non-destructively by performing measurements in the inhomogeneous stray-field outside the magnet system. Some of the sensors are also portable being thus well suited for onsite measurements. The gain of both bulk and depth-dependent microscopic properties are important for establishing improved structure-property relationships needed for the rational design of new polymer formulations. Selected recent applications will be presented to illustrate this potential of compact NMR.

The Fate of the Peroxyl Radical in Autoxidation: How Does Polymer Degradation Really Occur?

Bolland and Gee's basic autoxidation scheme (BAS) for lipids and rubbers has long been accepted as a general scheme for the autoxidation of all polymers. This scheme describes a chain process of initiation, propagation, and termination to describe the degradation of polymers in the presence of O₂. Central to this scheme is the conjecture that propagation of damage to the next polymer chain occurs via hydrogen atom transfer with a peroxyl radical. However, this reaction is strongly thermodynamically disfavored for all but unsaturated polymers, where the product allylic radical is resonance-stabilized. Paradoxically, there is no denying that the autocatalytic degradation and oxidation of saturated polymers still occurs. Critical analysis of the literature, described herein, has begun to unravel this mystery. One possibility is that the BAS still holds for saturated polymers but only at unsaturated defect sites, where H transfer is thermodynamically favorable. Another is that peroxyl termination rather than H transfer is dominant. If this were the case, tertiary peroxyl radicals (formed at quaternary centers or quaternary branching defects) may terminate to form alkoxy radicals, which can much more readily undergo chain transfer. This process would lead to the creation of hydroxy groups on the degraded polymer. On the other hand, primary and secondary peroxyl radicals would terminate to form nonradical products and halt further degradation. As a result, under this scenario the degree of branching and substitution would have a major effect on polymer stability. Herein we survey studies of polymer degradation products and of the effect of polymer structure on stability and show that indeed peroxyl termination is competitive with peroxyl transfer and possibly dominant under some conditions. It is also feasible that oxygen may not be the only reactive atmospheric species involved in catalyzing polymer degradation. Herein we outline plausible mechanisms involving ozone, hydroperoxyl radical, and hydroxyl radical that have all been suggested in the literature and can account for the experimentally observed formation of hydroperoxides without invoking peroxyl transfer. We also show that oxygen itself has even been reported to slow the degradation of poly(methyl methacrylate)s, which might be expected if peroxyl radicals are unreactive toward hydrogen transfer. Discrepancies between the rate of oxidation and the rate of degradation have been observed for polyolefins and also support the counterintuitive notion that oxygen stabilizes these polymers against degradation. We show that together these studies support alternative mechanisms for polymer degradation. A thorough assessment of kinetic studies reported in the literature indicates that they are limited by their propensity to use models based on the BAS, disregarding the chemical differences intrinsic to each class of polymer. Thus, we propose that further work must be done to fully grasp the complex mechanism of polymer degradation under ambient conditions. Nonetheless, our analysis of the literature points to measures that can be used to enhance or prevent polymer degradation and indicates that we should focus beyond just the role of oxygen toward the specific chemical nature and environment of the polymer at hand.

Use of Irradiated Polymers after Their Lifetime Period

This article deals with the study of the utilisation of irradiated HDPE products after their end-of-life cycle. Today, polymer waste processing is a matter of evermore intensive discussion. Common thermoplastic waste recycling-especially in the case of wastes with a defined composition-is generally well-known-and frequently used. On the contrary, processing cross-linked plastics is impossible to do in the same way as with virgin thermoplastics-mainly due to the impossibility of remelting them. The possibility of using waste in the form of grit or a powder, made from cross-linked High Density PolyEthylene (rHDPEx) products, after their end-of-life cycle, as a filler for virgin Low Density PolyEthylene (LDPE) was tested in a matrix. It was found that both the mechanical behaviour and processability of new composites with an LDPE matrix, with rHDPEx as a filler, depend-to a high degree-on the amount of the filler. The composite can be processed up to 60% of the filler content. The Polymer Mixture Fluidity dropped significantly, in line with the amount of filler, while the mechanical properties, on the other hand, predominantly grew with the increasing amount of rHDPEx.

Exploring the Long-Term Hydrolytic Behavior of Zwitterionic Polymethacrylates and Polymethacrylamides

The hydrolytic stability of polymers to be used for coatings in aqueous environments, for example, to confer anti-fouling properties, is crucial. However, long-term exposure studies on such polymers are virtually missing. In this context, we synthesized a set of nine polymers that are typically used for low-fouling coatings, comprising the well-established poly(oligoethylene glycol methylether methacrylate), poly(3-(N-2-methacryloylethyl-N,N-dimethyl) ammoniopropanesulfonate) ("sulfobetaine methacrylate"), and poly(3-(N-3-methacryamidopropyl-N,N-dimethyl)ammoniopropanesulfonate) ("sulfobetaine methacrylamide") as well as a series of hitherto rarely studied polysulfabetaines, which had been suggested to be particularly hydrolysis-stable. Hydrolysis resistance upon extended storage in aqueous solution is followed by ¹H NMR at ambient temperature in various pH regimes. Whereas the monomers suffered slow (in PBS) to very fast hydrolysis (in 1 M NaOH), the polymers, including the polymethacrylates, proved to be highly stable. No degradation of the carboxyl ester or amide was observed after one year in PBS, 1 M HCl, or in sodium carbonate buffer of pH 10. This demonstrates their basic suitability for anti-fouling applications. Poly(sulfobetaine methacrylamide) proved even to be stable for one year in 1 M NaOH without any signs of degradation. The stability is ascribed to a steric shielding effect. The hemisulfate group in the polysulfabetaines, however, was found to be partially labile.

Advanced Materials by Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) has been successfully employed for the preparation of various advanced materials with controlled architecture. New catalysts with strongly enhanced activity permit more environmentally benign ATRP procedures using ppm levels of catalyst. Precise control over polymer composition, topology, and incorporation of site specific functionality enables synthesis of well-defined gradient, block, comb copolymers, polymers with (hyper)branched structures including stars, densely grafted molecular brushes or networks, as well as inorganic-organic hybrid materials and bioconjugates. Examples of specific applications of functional materials include thermoplastic elastomers, nanostructured carbons, surfactants, dispersants, functionalized surfaces, and biorelated materials.

Chitosan/CaCO3-silane nanocomposites: Synthesis, characterization, in vitro bioactivity and Cu(II) adsorption properties

Chitosan nanocomposites containing 2, 5, 8wt% of calcium carbonate-γ-aminopropyl triethoxy silane (CS/CC-ATS NCs) were prepared by ultrasonic irradiation. After characterizing of physicochemical properties of the obtained CS/CC-ATS NCs, their performance was evaluated for both the bone-like apatite mineralization and the removal of Cu(II). The field emission-scanning electron microscopy images from the in vitro bioactivity of the CS and the CS/CC-ATS NC 5wt% displayed that the hydroxyapatite was produced on the samples surface. However, the distribution of it on the surface of CS/CC-ATS NC 5wt% was better than the pure CS. The uptake of Cu(II) on the CS/CC-ATS NC 5wt% was studied under different adsorption conditions such as contact time, the initial concentration of metal ion and adsorbent amount. The results of isothermal adsorption of the pure CS and the CS/CC-ATS NC 5wt% were well fitted by Langmuir model for Cu(II) with adsorption capacity of 33.33 and 33.90mg·g^-1, respectively. As a result, the CS/CC-ATS NC has great potencies in both the bone tissue engineering and the uptake of toxic metal from solution.

A Carbomethoxylated Polyvalerolactone from Malic Acid: Synthesis and Divergent Chemical Recycling

We report here the synthesis of a novel substituted polyvalerolactone from the renewable monomer, 4-carbomethoxyvalerolactone (CMVL, two steps from malic acid). The polymerization proceeds to high equilibrium monomer conversion to give the semicrystalline carbomethoxylated polyester with low dispersity. The material displays a glass transition temperature of -18 °C and two melting temperatures at 68 and 86 °C. This polymer can be chemically recycled by either of two independent pathways. The first (red) cleanly returns CMVL by a backbiting depolymerization from the hydroxy terminus; the second (blue) uses a base to cleave the polyester in a retro-oxa-Michael fashion. This affords a methacrylate-like monomer that we have polymerized radically to a new polymethacrylate analogue. This is a rare example of a polymer that has been shown to have two independent chemical recycling pathways leading to two different classes of monomers.

In Vitro Degradation Behaviors of Manganese-Calcium Phosphate Coatings on an Mg-Ca-Zn Alloy

In order to decrease the degradation rate of magnesium (Mg) alloys for the potential orthopedic applications, manganese-calcium phosphate coatings were prepared on an Mg-Ca-Zn alloy in calcium phosphating solutions with different addition of Mn2+. Influence of Mn content on degradation behaviors of phosphate coatings in the simulated body fluid was investigated to obtain the optimum coating. With the increasing Mn addition, the corrosion resistance of the manganese-calcium phosphate coatings was gradually improved. The optimum coating prepared in solution containing 0.05 mol/L Mn2+ had a uniform and compact microstructure and was composed of MnHPO4·3H2O, CaHPO4·2H2O, and Ca3(PO4)2. The electrochemical corrosion test in simulated body fluid revealed that polarization resistance of the optimum coating is 36273 Ωcm2, which is about 11 times higher than that of phosphate coating without Mn addition. The optimum coating also showed the most stable surface structure and lowest hydrogen release in the immersion test in simulated body fluid.