Vapor deposition of ultrathin hydrophilic polymer coatings enabling candle soot composite for highly sensitive humidity sensors

Candle soot (CS) is a desirable carbon nanomaterial for sensors owing to its highly porous nanostructure and large specific surface area. CS is advantageous in its low-cost and facile preparation compared to graphene and carbon nanotubes, but its pristine nanostructure is susceptible to collapse, hampering its application in electronic devices. This article reports conformal coating of nanoscale crosslinked hydrophilic polymer on CS film using initiated chemical vapor deposition, which well preserved the CS nanostructure and obtained nanoporous CS@polymer composites. Tuning coating thickness enabled composites with different morphologies and specific surface areas. Surprisingly, the humidity sensor made from composite with the lowest filling degree, thus largest specific surface area, showed relatively low sensitivity, which is likely due to its discontinuous structure, thus insufficient conductive channels. Composite sensor with optimum filling degree shows excellent sensing response of more than 10³ with the linearity of R² = 0.9400 within a broad relative humidity range from 11% to 96%. The composite sensor also exhibits outstanding sensing performance compared to literature with low hysteresis (3.00%), a satisfactory response time (28.69 s), and a fast recovery time (0.19 s). The composite sensor is fairly stable and durable even after 24 h soaking in water. Furthermore, embedding a humidity sensor into a face mask realizes real-time monitoring of human breath and cough, suggesting promising applications in respiratory monitoring.     

Roll-to-Roll Production of Spider Silk Nanofiber Nonwoven Meshes Using Centrifugal Electrospinning for Filtration Applications

Filtration systems used in technical and medical applications require components for fine particle deep filtration to be highly efficient and at the same time air permeable. In high efficiency filters, nonwoven meshes, which show increased performance based on small fiber diameters (e.g., using nanofibers), can be used as fine particle filter layers. Nanofiber nonwoven meshes made by electrospinning of spider silk proteins have been recently shown to exhibit required filter properties. Needle-based electrospinning, however, is limited regarding its productivity and scalability. Centrifugal electrospinning, in contrast, has been shown to allow manufacturing of ultrathin polymer nonwoven meshes in an efficient and scalable manner. Here, continuous roll-to-roll production of nonwoven meshes made of recombinant spider silk proteins is established using centrifugal electrospinning. The produced spider silk nanofiber meshes show high filter efficiency in the case of fine particulate matter below 2.5 µm (PM2.5) and a low pressure drop, resulting in excellent filter quality.     

Highly sensitive and ultrafast response surface acoustic wave humidity sensor based on electrospun polyaniline/poly(vinyl butyral) nanofibers

Polyaniline (PANi) composite nanofibers were deposited on surface acoustic wave (SAW) resonator with a central frequency of 433 MHz to construct humidity sensors. Electrospun nanofibers of poly(methyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(vinylidene fluoride), poly(vinyl butyral) (PVB) were characterized by scanning electron microscopy, and humidity response of corresponding SAW humidity sensors were investigated. The results indicated that PVB was suitable as a matrix to form nanofibers with PANi by electrospinning (ES). Electrospun PANi/PVB nanofibers exhibited a core–sheath structure as revealed by transmittance electron microscopy. Effects of ES collection time on humidity response of SAW sensor based on PANi/PVB nanofibers were examined at room temperature. The composite nanofiber sensor exhibited very high sensitivity of ∼75 kHz/%RH from 20 to 90%RH, ultrafast response (1 s and 2 s for humidification and desiccation, respectively) and good sensing linearity. Furthermore, the sensor could detect humidity as low as 0.5%RH, suggesting its potentials for low humidity detection. Attempts were done to explain the attractive humidity sensing performance of the sensor by considering conductivity, hydrophilicity, viscoelasticity and morphology of the polymer composite nanofibers.     

A Disposable Sensor Chip Using a Paste Electrode with Surface-Imprinted Graphite Particles for Rapid and Reagentless Monitoring of Theophylline

This work focuses on a carbon-based imprinted polymer composite, employed as a molecular recognition and sensing interface in fabricating a disposable electrochemical sensor. The carbon-paste electrode was made of a molecularly imprinted polymer comprising a copolymer of methacrylic acid as the functional monomer and blended crosslinking monomers of N,N′-methylenebisacrylamide, and ethylene glycol dimethacrylate, with theophylline as the template. The analytical properties of the proposed theophylline sensor were investigated, and the findings revealed an increase in differential pulse voltammetric current compared to the non-imprinted electrode. Under optimized conditions, the sensor has shown high sensitivity, high selectivity, lower detection limit (2.5 µg/mL), and satisfactory long-term stability. Further, the sensor was tested in whole bovine blood and validated without any matrix effect and cross-reactivity. Additionally, chronoamperometry of the sensor chip supported a rapid determination of THO with a short response time of 3 s. This carbon-paste electrode is highly specific for theophylline and may be applied as a drug sensor for clinical use.     

A simplified measurement procedure and portable electronic photometer for disposable sensors based on ionophore-chromoionophore chemistry for potassium determination

A field-portable photometer for potassium determination with disposable sensors has been developed. It can be applied to routine water and beverage analysis. The disposable sensor is based on ionophore-chromoionophore chemistry. A colour change in the sensing film is detected by measuring the transmitted intensity with a solid state photodetector. Optical excitation at 660 nm is emitted by a light-emitting diode (LED). Negative feedback for LED bias and thermal correction were included to improve system stability. Additionally, a measurement procedure is presented, characterized and validated for in situ photometer use and real-time results. This simplified procedure is based on prior preparation of the disposable sensor in its acidic form and on the use of an absorbance ratio as analytical parameter. The only requirement for analysis is prior equilibration with a buffered sample solution for 3 min and absorbance measurement before and after equilibration. Good sensitivity in the concentration range 5 μM to 100 mM and very good repetitively and stability were achieved that are comparable to those obtained with bulkier analytical instrumentation. Given the compact size, low weight, rapid response and low energy requirement of the electronic photometer developed here, this measurement system is suitable for potassium determination in the field.     

Disposable chemiluminometric sensor for rapid determination of EDTA

A new chemiluminescence-based disposable sensor for EDTA is described. The EDTA-sensitive element is a transparent bilayer membrane containing Ru(Bipy)₃ ²⁺ complex and Ce(IV), respectively, on a polyester support. The sample is injected by means of a syringe, acting pneumatically, into a 10 mm cell containing the CL membrane and placed in the external holder of a luminometer. The composition of the membrane and reaction conditions have been adjusted to obtain adequate sensitivity and selectivity. The disposable sensor responds to EDTA rapidly over a dynamic range from 6.6 × 10⁻⁶ M to 7.0 × 10⁻⁴ M, with sensor-to-sensor reproducibility around 6% as RSD (relative standard deviation) at the medium level of the range. The performance of the optical disposable sensor was tested for the analysis of EDTA in ophthalmic collyrium and different types of sauce samples, validating the results against a reference procedure. The sensing approach presented here demonstrates the feasibility of chemiluminescent disposable sensors for quantitative analysis with good features.     

Evaluation of Leaf Mineral,Flavonoid, and Total Phenolic Content in Spider Plant Germplasm

Spider plant (Cleome gynandra L.) is an important leafy vegetable that grows naturally in many parts of the world. The leaves are highly nutritious and are used mainly for human consumption. The mineral content and phenolic compounds of 17 genotypes (local and exotic) of spider plant and four standards (swiss chard, jute mallow, cowpea, and pumpkin) were investigated. Leaf samples were harvested from plants raised at Thohoyandou, South Africa. Exotic genotypes were superior to local genotypes for most of the minerals. Swiss chard possessed significantly high levels of some minerals such as iron and manganese in comparison with exotic spider plant genotypes. The calcium content in the local (‘MP-B-3-CG’) and exotic (‘GPS’) genotypes was >30.0% and >60.0% higher than in swiss chard, respectively. Total phenolics among spider plant genotypes ranged from 9.86 to 12.21 mg GAE/g DW and were superior to pumpkin. In addition, the spider plant genotypes varied significantly in the antioxidant capacity as estimated by the 2,2 diphenyl-1-picrylhydrazyl method and ferric-reducing antioxidant power. The main flavonoid in the leaves of spider plant genotypes was quercetin-3-rutinoside. Crotonoside (glycoside) was detected in all the spider plant genotypes and swiss chard. A positive correlation was observed between total phenolic content and each of the three flavonoids. The PCA biplot associated exotic genotypes (‘ML-SF-29′, ‘PS’, ‘TZ-1’, and ‘GPS’) and local genotypes (‘ML-3-KK’, ‘ML-13-SDM’, and ‘ML-12-TMP’) with high Al, Fe, Zn, N, and TPC. Cluster analysis indicated high “distant groups” between exotic and local genotypes of spider plant. These results indicated that some of the local germplasm of spider plant was largely inferior to the exotic germplasm in terms of their mineral composition but contained considerable quantities of quercetin-3-rutinoside, particularly in the local genotypes ‘MP-B-2-CG’ and ‘MP-B-1-CG’. There is a need for genetic improvement of the local germplasm in some of the minerals particularly to benefit the end-users.     

Integrated dielectrophoretic and impedimetric biosensor provides a template for universal biomarker sensing in clinical samples

The detection and quantification of nucleic acid and proteomic biomarkers in bodily fluids is a critical part of many medical screening and diagnoses. However, majority of the current detection platforms are not ideal for routine, rapid, and low-cost testing in point-of-care settings. To address this issue, we developed a concept for a disposable universal point-of-care biosensor that can detect and quantify nucleic acid and proteomic biomarkers in diluted serum samples. The central tenet of sensing is the use of dielectrophoresis, electrothermal effects, and thermophoresis to selectively and rapidly isolate the biomarkers of interest in electrodes and then quantify using electrical impedance. When the sensor was applied to quantify microRNA and antigen biomarker molecules directly in diluted serum samples, it produced a LOD values in the fM range and sensitivity values from 10¹² to 10¹⁵ Ω/M with a 30 min assay time and assay cost of less than $50 per assay.     

alpha-Cyclodextrin-modified infrared sensing system for rapidly determining the enantiomeric composition of chiral compounds

This paper describes a new infrared (IR) sensing method for rapidly determining the enantiomeric compositions of chiral compounds through the use of a chirality-selective compound immobilized on the surface of the evanescent-wave sensing elements. α-Cyclodextrin (α-CD) was selected as this agent and it was immobilized on a zinc selenide sensing element to allow different analytical signals to be generated for each compound of a pair of enantiomers. Theoretical working equations were developed to monitor the response of the ATR-IR spectroscopic sensor during this process. The difference between the formation constants of enantiomers was crucial to the sensitivity when determining the enantiomeric compositions. Control of the pH of the solution could be used to effectively increase the difference between these formation constants. Based on the static sensing system with optimal conditions, the ratio of the values of the signals of the two enantiomers was <0.4. A linear relationship between the analytical signals and the mole fraction of the enantiomers was obtained under conditions in which the concentration of the chiral compound was sufficiently low. Based on the detected time profiles, this sensing method had a fast response: the detection time could be <10 min. With a flow-cell configuration, the time to finish one determination can be shorter than 10 min with similar sensitivity and accuracy as in static sensing system.     

Study on low-cost calibration-free pH sensing with disposable optical sensors

As labor costs become more expensive, less labor-intensive disposable devices have become more ubiquitous. Similarly, the disposable optical pH sensor developed in our lab could provide a convenient yet cost-effective way for pH sensing in processes that require stringent pH control. This optical pH sensor is prepared in uniform individual lots of 100–200 sensors per lot. Calibration is accomplished on a few randomly selected sensors out of each lot. We show that all others in the same lot can then be used directly without requiring individual calibration. In this paper, a calibration model is derived to include all the factors that affect the signal of the disposable sensor. Experimental results show that the derived calibration model fits the experimental data. The readings of 28 randomly selected disposable sensors with 4 sensors from each of the 7 lots show an error less than 0.1 pH units in the useful sensing range of the sensor. The calibration model indicates that if further improvement on precision is desired, more uniform porous material and more advanced coating techniques will be required. When it comes to the effects of the varying coasters, house-made low-cost fluorometers, the variability in the brightness ratio of the blue-to-violet LEDs is the primary reason for the lack of precision. Other factors like LED light intensity distribution, optical properties of the filters and electronics also contribute to the coaster-to-coaster difference, but to a lesser extent. Two different methods for correcting the instrument variations were introduced. After correction, the collective reading errors for all the tested instruments were reduced to less than 0.2 pH units within the sensor's useful sensing range. Based on this result, our lab is currently implementing further improvements in modifying the coasters to equalize the ratios of blue-to-violet LED brightness.     

Changes in Amino Acid Profiles and Bioactive Compounds of Thai Silk Cocoons as Affected by Water Extraction

Silk proteins have many advantageous components including proteins and pigments. The proteins—sericin and fibroin—have been widely studied for medical applications due to their good physiochemical properties and biological activities. Various strains of cocoon display different compositions such as amino-acid profiles and levels of antioxidant activity. Therefore, the objectives of this study were to find a suitable silk protein extraction method to obtain products with chemical and biological properties suitable as functional foods in two strains of Bombyx mori silk cocoon (Nangsew strains; yellow cocoon) and Samia ricini silk cocoon (Eri strains; white cocoon) extracted by water at 100 °C for 2, 4, 6 and 8 h. The results showed that Nangsew strains extracted for 6 h contained the highest amounts of protein, amino acids, total phenolics (TPC) and total flavonoids (TFC), plus DPPH radical-scavenging activity, ABTS radical scavenging capacity, and ferric reducing antioxidant power (FRAP), anti-glycation, α-amylase and α-glucosidase inhibition. The longer extraction time produced higher concentrations of amino acids, contributing to sweet and umami tastes in both silk strains. It seemed that the bitterness decreased as the extraction time increased, resulting in improvements in the sweetness and umami of silk-protein extracts.     

Presence of β-Turn Structure in Recombinant Spider Silk Dissolved in Formic Acid Revealed with NMR

Spider dragline silk is a biopolymer with excellent mechanical properties. The development of recombinant spider silk protein (RSP)-based materials with these properties is desirable. Formic acid (FA) is a spinning solvent for regenerated Bombyx mori silk fiber with excellent mechanical properties. To use FA as a spinning solvent for RSP with the sequence of major ampullate spider silk protein from Araneus diadematus, we determined the conformation of RSP in FA using solution NMR to determine the role of FA as a spinning solvent. We assigned ¹H, ¹³C, and ¹⁵N chemical shifts to 32-residue repetitive sequences, including polyAla and Gly-rich regions of RSP. Chemical shift evaluation revealed that RSP is in mainly random coil conformation with partially type II β-turn structure in the Gly-Pro-Gly-X motifs of the Gly-rich region in FA, which was confirmed by the ¹⁵N NOE data. In addition, formylation at the Ser OH groups occurred in FA. Furthermore, we evaluated the conformation of the as-cast film of RSP dissolved in FA using solid-state NMR and found that β-sheet structure was predominantly formed.     

Humidity sensors using in situ synthesized sodium polystyrenesulfonate/ZnO nanocomposites

Thin film humidity sensors have been prepared using in situ synthesized inorganic/organic nanocomposites of sodium polystyrenesulfonate (NaPSS) and ZnO. Its humidity sensing characteristics and the sensing mechanism have been investigated by measuring the complex impedance spectra of the sensor at different humidities. The logarithm of the impedance of sensor based on composite film changes linearly by four-orders of magnitude over almost whole humidity range (11-97% RH). Furthermore, the sensor exhibits a quick response (absorption: 2 s, desorption: 2 s) and small hysteresis (less than 2% RH). The composite film shows better sensing properties than NaPSS film, such as better linearity, quicker response. Explanation to the improvement is attempted by taking into account of the composition and structure of the nanocomposites.     

A resistive-type humidity sensor using composite films prepared from poly(2-acrylamido-2-methylpropane sulfonate) and dispersed organic silicon sol

A composite material of dispersed organic silicon sol and poly(2-acrylamido-2-methylpropane sulfonate) (poly-AMPS) was used to make humidity sensor without protective film or complicated chemical procedures. The organic silicon sol was dispersed well in the poly-AMPS without using dispersion agent. Parameters that may affect the water-resistive but humidity-sensitive characteristic of composite material, the adding amount of organic silicon sol solution and the film of thermal treatment time, were investigated. The microstructure of the material was analyzed, and the humidity sensing and electrical properties of the sensor were measured. The sensor well responded to humidity with a relatively good linearity, though it depended on the applied frequency. The temperature influence between 15 and 35 °C was within −0.17 % relative humidity (RH)/°C in the range of 30–90% RH. The activation energy was maximum around 40% RH. The sensor showed the hysteresis within 5.9%, fast response time, long-term stability (75 days at least) and satisfactory resistance to high humidity atmosphere (97% RH) and chemical environment (20% C₂H₅OH vapor). Analyzing the structure and complex impedance plots of organic silicon sol/poly-AMPS was used to explain improvement in humidity sensing properties in comparison with nano-sized SiO₂ powder/poly-AMPS films.     

一种天然纳米纤维捕鸟蛛丝的物理化学结构表征

蜘蛛丝作为功能性结构材料, 其独特的纤维成型方法与优良的结构和性能引起许多人的关注. 从20世纪80年代开始有关蜘蛛丝的研究报道日益增加[1]. 与高温高压下或由溶剂纺丝成型的合成纤维相比, 蜘蛛丝在空气中凝固成型, 丝纤维成型安全、无害, 从腹部若干不同吐丝器产生不同种类的丝具有不同的用途[2]. 蜘蛛拖曳丝(dragline silk)的比强度大于钢丝, 且具有较大的断裂伸长率(9%～30%)[3,4], 抗张强度1.1～1.4 GPa. 在相对湿度50%和应变速率100%/min的条件下, 模量值可达10～50 GPa. 在所有已知纤维品种中, 蜘蛛丝的断裂能是最高的. 此外, 蜘蛛丝在许多方面的综合性能优于最优良的人造纤维. 另外, 蜘蛛丝的细度为已知纤度最小的天然有机纤维, 这种高性能丝具有捕捉昆虫甚至鸟类的功能, 因此蜘蛛丝是具有特异功能的天然纤维材料. 目前, 蜘蛛丝结构和性能的研究主要包括其化学组成[5]、结晶结构[6,7]、结构模型[8,9]以及其NMR表征[10]等, 这些研究揭示了蜘蛛丝的氨基酸组成、分子量及其分布、结晶度、晶胞尺寸、链构象以及结构模型等. 这些研究主要集中在少数几种蜘蛛品种上, 如金色圆网织网蛛(Nephila clavipes)、十字圆蛛(A.diadematus)和大腹圆蛛(A.ventrocosus)等. 目前, 已知的蜘蛛种类大于30 000种[11], 以蜘蛛丝为例的生物大分子材料研究是一个挑战性的课题. 国内蜘蛛丝的研究仅有大腹圆蛛拖曳丝蛋白一级结构的研究报道[12,13]. 本文报道了广西捕鸟蛛丝的红外光谱、形貌结构和原子力显微镜的初步研究结果.     

WISE NMR characterization of nanoscale heterogeneity and mobility in supercontracted Nephila clavipes spider dragline silk

The addition of water to spider dragline silk results in fiber contraction to 50% its initial length and significant changes to the mechanical properties of the silk. This event has been termed supercontraction. A decrease in strength and increase in elasticity have been reported when the silk is in contact with water. Two-dimensional wide-line separation (WISE) nuclear magnetic resonance (NMR) is implemented to correlate (13)C chemical shifts with mobility by observing the corresponding (1)H line widths and line shapes in water-saturated spider dragline silk. The WISE NMR spectrum of the native silk exhibits (1)H line widths that are approximately 40 kHz for all carbon environments characteristic of a rigid organic system. In contrast, the water-saturated case displays a component of the (1)H line that is narrowed to approximately 5 kHz for the glycine C(alpha) and a newly resolved alanine helical environment while the alanine C(beta) corresponding to the beta-sheet conformation remains broad. These results indicate that water permeates the amorphous, glycine-rich matrix and not the crystalline, polyalanine beta-sheets. A delay time is added to the WISE NMR pulse sequence to monitor spin diffusion between the amorphous, mobile region and the crystalline domains. The time required for spin diffusion to reach spatial equilibrium is related to the length scale of the polyalanine crystallites. This technique is employed to measure crystalline domain sizes on the nanometer length scale in water-solvated spider dragline silk. These results provide further insight into the structure of spider silk and mechanism of supercontraction.     

Potentiometric Surfactant Sensor Based on 1,3-Dihexadecyl-1H-benzo[d]imidazol-3-ium for Anionic Surfactants in Detergents and Household Care Products

A 1,3-dihexadecyl-1H-benzo[d]imidazol-3-ium-tetraphenylborate (DHBI-TPB) ion-pair implemented in DHBI-TPB surfactant sensor was used for the potentiometric quantification of anionic surfactants in detergents and commercial household care products. The DHBI-TPB ion-pair was characterized by FTIR spectroscopy and computational analysis which revealed a crucial contribution of the C–H∙∙∙π contacts for the optimal complex formation. The DHBI-TPB sensor potentiometric response showed excellent analytical properties and Nernstian slope for SDS (60.1 mV/decade) with LOD 3.2 × 10⁻⁷ M; and DBS (58.4 mV/decade) with LOD 6.1 × 10⁻⁷ M was obtained. The sensor possesses exceptional resistance to different organic and inorganic interferences in broad pH (2–10) range. DMIC used as a titrant demonstrated superior analytical performances for potentiometric titrations of SDS, compared to other tested cationic surfactants (DMIC > CTAB > CPC > Hyamine 1622). The combination of DHBI-TPB sensor and DMIC was successfully employed to perform titrations of the highly soluble alkane sulfonate homologues. Nonionic surfactants (increased concentration and number of EO groups) had a negative impact on anionic surfactant titration curves and a signal change. The DHBI-TPB sensor was effectively employed for the determination of technical grade anionic surfactants presenting the recoveries from 99.5 to 101.3%. The sensor was applied on twelve powered samples as well as liquid-gel and handwashing home care detergents containing anionic surfactants. The obtained results showed good agreement compared to the outcomes measured by ISE surfactant sensor and a two-phase titration method. The developed DHBI-TPB surfactant sensor could be used for quality control in industry and has great potential in environmental monitoring.     

Fluorescence resonance energy transfer disposable sensor for copper(II)

A disposable sensor has been developed for the measurement of copper(II) concentration in aqueous solution based on a change in the fluorescence of porphyrazine 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine (TP). The sensor was constructed by spin-coating a polyester support with a PVC solution containing TP, a plasticizer, the chelating agent Zincon and the ion-pairing benzetonium chloride. The measurement principle is based on the radiationless resonance energy transfer (RET) from TP immobilized in membrane, and acting as fluorescence donor, to Zincon acting as an acceptor induced by copper(II). The absorption spectrum of the Zincon-Cu(II) complex presents adequate overlapping with the emission spectrum of TP, producing a useful analytical signal by the RET process.The disposable sensor responds to copper(II) irreversibly over a dynamic range from 0.039 to 14 μmol L⁻¹ (2.5-890 μg L⁻¹) with a sensor-to-sensor reproducibility (relative standard deviation RSD) of 1.9%, as log aCu2+, at the medium level of the range and a response time of 10 min. The performance of the optical disposable sensor was tested for the analysis of copper in different types of natural waters (river, well, spring and swimming pool), validating results against a reference procedure.     

Sensing mechanism of Pd-doped SnO2 sensor for LPG detection

In the present work, studies have been made to analyze the sensitivity, response, recovery time and sensing mechanism of Pd-doped thick film SnO₂ sensor for detection of LPG. To achieve this, thick film Pd-doped (0.25 and 1% by weight in available Indium doped SnO₂ thick film paste supplied by ESL, USA) along with an undoped (Indium doped) SnO₂ sensors were fabricated on a 1″ × 1″ alumina substrate. It consists of a gas sensitive layer (doped SnO₂), a pair of electrodes underneath the gas sensing layer serving as a contact pad for sensor. Also, a heater element on the backside of the substrate was printed for generating appropriate operating temperature at the substrate necessary for acquiring gas sensing properties. The sensor doped with 1% palladium showed the maximum sensitivity of 72% at 350 °C for 0.5% concentration of LPG. Possible detailed sensing mechanism of Pd-doped SnO₂ sensor for LPG detection has been proposed.     

Spinnenseidenproteine: Grundlage für neue Materialien

Spider silk is a biomaterial with extraordinary properties. It is extremely tough and at the same time highly elastic – a combination not found in other polymers. Due to its outstanding potential, spider silk has long been desired as a material for technical applications. This review highlights recent developments in the field of spider silk technology, insights into silk structure, and the natural silk spinning process. Due to the recent progress, spider silk products might be available in the near future, reflecting a new generation of environmentally friendly polymer products.