Molecular Weight Distribution Research Articles

Three anti-inflammatory polysaccharides from Lonicera japonica Thunb.: Insights into the structure-function relationships

This study demonstrates the feasibility of producing three polysaccharides (neutral LJP-1, acidic LJP-2 and acidic LJP-3) with significant in vitro and in vivo anti-inflammatory activities from the flowers of Lonicera japonica. The three polysaccharides differed in chemical composition, molecular weight distribution, glycosidic linkage pattern, functional groups and morphology. They exhibited excellent protective effects (in a dose-dependent manner) in lipopolysaccharide-injured RAW264.7 macrophages and CuSO4-damaged zebrafish via reducing NO production and inhibiting the overexpressions of inflammation-related transcription factors, inflammatory proteins and cytokines in the NF-κB/MAPK signaling pathways. Their anti-inflammatory effects varied owing to their different molecular characteristics and chemical compositions. Overall, LJP-2 at 400μg/mL was the most effective. LJP-2 consisted mainly of → 5)-α-L-Araf (1→, →4)-α-L-GalpA (1→ and →2)-α-L-Rhap (1→ residues with terminal T-β-D-Glcp. Thus, honeysuckle flowers are good sources of anti-inflammatory polysaccharides, and precise fractionation enables the production of potent anti-inflammatory agents for the development of functional foods and healthcare products.

Leveraging Electron Push-Pull Effect for Catalytic Polymerization and Degradation of a Cyclobutane Monomer System.

Ring-opening polymerization (ROP) offers a striking solution to solve problems encountered in step-growth condensation polymerization, including precise control over molecular weight, molecular weight distribution, and topology. This has inspired our interest in ROP of cycloalkanes with an ultimate goal to rethink polyolefins, which clearly poses a number of challenges. Practicality of ROP of cycloalkanes is actually limited by their low polymerizability and elusive mechanisms which arise from significantly varied ring size and non-polar C-C bonds in monomers. In this work, by using Lewis acid/Brønsted base/C(sp3)-H initiator system previously developed in our laboratory, we focus on cyclobutanes and explore the positional and electronic effects of substituents on the ring, namely electron push-pull effect, in promoting controlled polymerization to afford densely functionalized poly(cyclobutanes), as well as catalytic degradation of obtained polymers for upcycling. More importantly, experiments and DFT calculations unveil considerable population of Lewis-acid-induced thermostabilized 1,4-zwitterions, which distinguish cyclobutanes from cyclopropanes and others. All these findings would shed light on catalytic synthesis and degradation of saturated all-carbon main-chain polymers, as well as small molecule transformations of cyclobutanes.

Leveraging Electron Push‐Pull Effect for Catalytic Polymerization and Degradation of a Cyclobutane Monomer System

AbstractRing‐opening polymerization (ROP) offers a striking solution to solve problems encountered in step‐growth condensation polymerization, including precise control over molecular weight, molecular weight distribution, and topology. This has inspired our interest in ROP of cycloalkanes with an ultimate goal to rethink polyolefins, which clearly poses a number of challenges. Practicality of ROP of cycloalkanes is actually limited by their low polymerizability and elusive mechanisms which arise from significantly varied ring size and non‐polar C−C bonds in monomers. In this work, by using Lewis acid/Brønsted base/C(sp3)‐H initiator system previously developed in our laboratory, we focus on cyclobutanes and explore the positional and electronic effects of substituents on the ring, namely electron push‐pull effect, in promoting controlled polymerization to afford densely functionalized poly(cyclobutanes), as well as catalytic degradation of obtained polymers for upcycling. More importantly, experiments and DFT calculations unveil considerable population of Lewis‐acid‐induced thermostabilized 1,4‐zwitterions, which distinguish cyclobutanes from cyclopropanes and others. All these findings would shed light on catalytic synthesis and degradation of saturated all‐carbon main‐chain polymers, as well as small molecule transformations of cyclobutanes.

Understanding the Ecological Robustness and Adaptability of the Gut Microbiome in Plastic-Degrading Superworms (Zophobas atratus) in Response to Microplastics and Antibiotics.

Recent discoveries indicate that several insect larvae are capable of ingesting and biodegrading plastics rapidly and symbiotically, but the ecological adaptability of the larval gut microbiome to microplastics (MPs) remains unclear. Here, we described the gut microbiome assemblage and MP biodegradation of superworms (Zophobas atratus larvae) fed MPs of five major petroleum-based polymers (polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate) and antibiotics. The shift of molecular weight distribution, characteristic peaks of C═O, and metabolic intermediates of residual polymers in egested frass proved depolymerization and biodegradation of all MPs tested in the larval intestines, even under antibiotic suppression. Superworms showed a wide adaptation to the digestion of the five polymer MPs. Antibiotic suppression negatively influenced the survival rate and plastic depolymerization patterns. The larval gut microbiomes differed from those fed MPs and antibiotics, indicating that antibiotic supplementation substantially shaped the gut microbiome composition. The larval gut microbiomes fed MPs had higher network complexity and stability than those fed MPs and antibiotics, suggesting that the ecological robustness of the gut microbiomes ensured the functional adaptability of larvae to different MPs. In addition, Mantel's test indicated that the gut microbiome assemblage was obviously related to the polymer type, the plastic degradability, antibiotic stress, and larval survival rate. This finding provided novel insights into the self-adaptation of the gut microbiome of superworms in response to different MPs.

Variation of SARA fractions of crumb rubber modified asphalt binder-aggregate interface system and its correlation with adhesion properties

The incorporation of rubber powder leads to a high degree of complexity in the CRMA binder-aggregate interfacial properties, which directly affects the interfacial adhesion performance. The objective of this study is to investigate the variation of SARA fractions of CRMA binder during the adhesion process and to explore the intrinsic relationship between the components and the adhesion properties. To this end, the staged extraction tests were performed to extract CRMA binder layers on the aggregate surface. After each extraction, the binder layer was evaluated in terms of its SARA fraction contents and molecular weight distribution. Additionally, the pull-off tensile strength (POTS) was used to assess the adhesion of the binder-aggregate interface through the binder bond strength (BBS) test. Finally, the correlation between the SARA fractions of CRMA binder and interface adhesion of CRMA binder-aggregate system was analyzed. The results showed that the CR tends to absorb the lighter components of base asphalt, the variations in SARA fractions and molecular weight distribution during the aggregate adhesion to CRMA binders occurred mainly in the third and fourth elution layers. Pen 70 CRMA binder and limestone show the best adhesion properties among all the binder and aggregate types. The increase in CR size and the decrease in CR dosage are favorable for the adhesion of CRMA binders to aggregates. Furthermore, asphaltenes and resins are positively correlated with adhesion, while aromatics and saturants are negatively correlated with adhesion. The correlation between SARA content and adhesion varied depending on the aggregate type.

Comparison of protein digestibility of human milk and infant formula using the INFOGEST method under infant digestion conditions.

Many improvements have been made to bring infant formula (IF) closer to human milk (HM) regarding its nutritional and biological properties. Nevertheless, the protein components of HM and IF are still different, which may affect their digestibility. This study aimed to evaluate and compare the protein digestibility of HM and IF using the infant INFOGEST digestion method. Pooled HM and a commercial IF were subjected to the infant INFOGEST method, which simulates the physiological digestion conditions of infants, with multiple directions, i.e., the curd state, SDS-PAGE, molecular weight distribution, free amino acid concentration, and in vitro protein digestion rate. HM underwent proteolysis before digestion, and tended to have a higher protein digestion rate with finer curds during gastric digestion, than the IF. However, multifaceted analyses showed that the protein digestibility of HM and IF was not significantly different after gastrointestinal digestion. In conclusion, the infant INFOGEST method showed that the digestibility of HM and IF proteins differed to some extent before digestion and after gastric digestion, but not at the end of gastrointestinal digestion. The findings of this study will contribute to the refinement of IFs with better protein digestibility in infant stomach.

Co-Immobilization of Alcalase/Dispase for Production of Selenium-Enriched Peptide from Cardamine violifolia.

Enzymatically derived selenium-enriched peptides from Cardamine violifolia (CV) can serve as valuable selenium supplements. However, the industrial application of free enzyme is impeded by its limited stability and reusability. Herein, this study explores the application of co-immobilized enzymes (Alcalase and Dispase) on amino resin for hydrolyzing CV proteins to produce selenium-enriched peptides. The successful enzyme immobilization was confirmed through scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and Fourier-transform infrared spectroscopy (FTIR). Co-immobilized enzyme at a mass ratio of 5:1 (Alcalase/Dispase) exhibited the smallest pore size (7.065 nm) and highest activity (41 U/mg), resulting in a high degree of hydrolysis of CV protein (27.2%), which was obviously higher than the case of using free enzymes (20.7%) or immobilized Alcalase (25.8%). In addition, after a month of storage, the co-immobilized enzyme still retained a viability level of 41.93%, showing fairly good stability. Encouragingly, the selenium-enriched peptides from co-immobilized enzyme hydrolysis exhibited uniform distribution of selenium forms, complete amino acid fractions and homogeneous distribution of molecular weight, confirming the practicality of using co-immobilized enzymes for CV protein hydrolysis.

Sulfobetaine Zwitterions with Embedded Fluorocarbons: Synthesis and Interfacial Properties.

We describe the preparation of a new set of fluorinated sulfobetaine (FSB) zwitterionic polymers in which fluorocarbon moieties are attached directly to the zwitterionic components. An efficient two-step modification to the conventional sulfobetaine methacrylate monomer synthesis gave access to a series of polymer zwitterions containing varying extents of fluorocarbon character. FSB methacrylates proved amenable to homo- and copolymerizations using reversible addition-fragmentation chain transfer (RAFT) conditions, affording polymers with molecular weights ranging from 5 to 20 kDa and with low molecular weight distributions. Thin films of FSB homopolymers on glass proved stable to aqueous environments and exhibited increasing hydrophobicity with fluorocarbon content, as well as remarkably large water contact angle hysteresis values that enable pinning of water droplets on hydrophobic surfaces, reminiscent of the "petal effect" found in nature. FSB-containing copolymers in aqueous media demonstrated markedly reduced oil-water interfacial tension values, even with moderate (20-50 mol %) FSB incorporation.

Type of pectin affects the functionality of potato protein-pectin conjugates in emulsions

This study investigated the effect of the molecular structure of pectin on conjugate formation and its functionality in plant protein-based emulsions. For this purpose, high-methoxylated, low-methoxylated, amidated citrus pectin and their mixtures with potato protein were vacuum-dried at defined process conditions. The change in free amino groups, colour and molecular weight distribution assessed conjugation. The side reaction, such as pectin degradation, was monitored by the degree of methoxylation, galacturonic acid content and intrinsic viscosity. In addition, FT-IR and hydrophobicity measurements were performed to determine the changes in chemical structure due to the occurring reactions. The ζ-potential, solubility and oil droplet size reflected the functionality of the conjugated samples.The results confirm that, apart from the conjugation of protein and pectin, where the most significant decrease in free amino groups was obtained with an increasing degree of methoxylation or presence of amide groups, undesirable degradation of pectin occurring, resulting in a broad molecular weight distribution of the conjugate samples. The conjugate formation was the highest with amidated pectin. The FT-IR measurements confirmed the formation of Maillard conjugates. The FT-IR spectra showed a decrease in the intensity signals of amide I and amide II and the formation of new C–N bond maxima. In addition, the conjugation caused the shift of the protein's isoelectric point to the acidic environment, resulting in higher solubility and improved emulsion stability at the isoelectric point of the protein.Regarding emulsion stability, the conjugates with amidated pectin performed best and achieved the narrowest oil droplet size distribution over a wider pH range. Emulsion-stabilising properties of conjugates with high- and low-methoxylated pectin differed only slightly. To better understand the underlying mechanisms for emulsion stabilisation, future research will focus on the interfacial properties of the conjugates as determined by interfacial shear rheology and pendant drop analysis.

A recombinant amylomaltase from Thermus thermophilus STB20 can tailor the macromolecular characteristics of tapioca starch through its transglycosylation activity

Amylomaltase (AM) is a transglucosylase known for producing glucans exclusively with α-1,4 linkages, which is widely used in the industries for modification of starch. In this paper, a study was conducted to investigate both the characteristics of recombinant amylomaltase from Thermus thermophilus STB20 (TtAM) and its impact on the fine structure of tapioca starch. The TtAM showed an excellent thermostability and a high affinity for larger molecular substrates. Changes in the molecular characteristics of tapioca starch were discussed in terms of chain length distribution (CLD) and molecular weight distribution (Mw) under different enzyme dosages and reaction times. The TtAM degraded amylose, which was transferred to short side chains (DP 11-26) of amylopectin, thereby extending short side chains into longer chains (DP >26). The Mw of TtAM-treated starches initially increased and then decreased. With increasing enzyme dosage and reaction time, the TtAM facilitated hydrolysis activities, reducing the proportion of long side chains, which led to increase the dextrose equivalent (DE) value. Cycloamylose (DP 8 - 33) was generated during the modification process, reflecting a diversified range of the enzyme products, and resulting in a polymodal distribution profile in the Mw. These findings potentially broaden the utilization of TtAM in the production of starch conversion products, indicating that novel starch-based derivatives with tailor-made structures can be obtained by controlling the enzyme dosages and reaction times.

Structural characterization of Astragalus polysaccharide-D1 and its improvement of low-dose metformin effect by enriching Staphylococcus lentus

To explore the adjuvant therapy drugs of low-dose metformin, one homogeneous polysaccharide named APS-D1 was purified from Astragalus membranaceus by DEAE-52 cellulose and Sephadex G-100 column chromatography. Its chemical structure was characterized by molecular weight distribution, monosaccharide composition, infrared spectrum, methylation analysis, and NMR. The results revealed that APS-D1 (7.36 kDa) consisted of glucose, galactose, and arabinose (97.51 %:1.56 %:0.93 %). It consisted of →4)-α-D-Glcp-(1→ residue backbone with →3)-β-D-Galp-(1→ residue and terminal-α/β-D-Glcp-(1→ side chains. APS-D1 could significantly improve inflammation (TNF-α, LPS, and IL-10) in vivo. Moreover, APS-D1 improved the curative effect of low-dose metformin without adverse events. APS-D1 combined with low-dose metformin regulated several gut bacteria, in which APS-D1 enriched Staphylococcus lentus to produce l-carnitine (one of 136 metabolites of S. lentus). S. lentus and l-carnitine could improve diabetes, and reduction of S. lentusl-carnitine production impaired diabetes improvement. The combination, S. lentus, and l-carnitine could promote fatty acid oxidation (CPT1) and inhibit gluconeogenesis (PCK and G6Pase). The results indicated that APS-D1 enhanced the curative effect of low-dose metformin to improve diabetes by enriching S. lentus, in which the effect of S. lentus was mediated by l-carnitine. Collectively, these findings support that low-dose metformin supplemented with APS-D1 may be a favorable therapeutic strategy for type 2 diabetes.

Characterization, antioxidant and α-amylase inhibition of polysaccharides and phosphorylated derivatives from finger citron (Citrus medica L. var. sarcodactylis Swingle)

In this study, the structure-activity relationship of finger citron polysaccharides (FCPs) and their phosphorylated derivatives (P-FCPs) was investigated. Three FCPs (FCP20, FCP40 and FCP60) were successively fractionated by ethanol, and were phosphorylated modification to obtain P-FCPs (P-FCP20, P-FCP40 and P-FCP60). FCPs and P-FCPs are acidic heteropolysaccharides composed of mannose, rhamnose, glucose, galactose, arabinose and galacturonic acid, and exhibited different content of neutral sugar, uronic acid, proteins, polyphenols and sulfates. FTIR and NMR analyses determined the structures of FCPs and P-FCPs, indicating that the phosphorylation modification was successful. P-FCPs possessed the smaller molecular weight distribution and particle size, with significant changes in microstructure than FCPs. Additionally, P-FCPs showed significantly increased antioxidant and α-amylase inhibitory activities compared to FCPs. The inhibitory mechanisms of FCP40 and P-FCP40 on α-amylase was a mixed-type manner and dynamic fluorescence quenching. The results demonstrate that phosphorylation modification can alter the structural features and bioactivities of FCPs, providing an approach for the further development of finger citron in the field of medicinal and functional foods.

Comparison of characterization and composition of melanoidins from three different dried apple slices

The composition of melanoidins in dried apple that affects quality remains unclear. The composition and structure of melanoidins in dried apple slices by hot air drying (HAAM), instant controlled pressure drop drying (DICAM), and vacuum freeze-drying (FDAM) were investigated. It showed that the melanoidins were highly heterogeneous mixtures with a light-yellow color and blue-green fluorescence, belonging to polysaccharide-type melanoidins. Specifically, HAAM had a large molecular weight (929.5 g/mol) and wide molecular weight distribution, with more double-bond conjugated systems. DICAM (610.9 g/mol), possessing the strongest fluorescence intensity, was mainly composed of compounds with fewer π-conjugated structures and more electron-donating groups. As a control, the low level of Maillard reaction in FDAM resulted in the formation of the smallest molecular weight (458.6 g/mol) with weak fluorescence intensity. Moreover, 10 compounds were tentatively identified in apple melanoidins. This study provides the foundation for the future functional preparation of apple melanoidins.

Evidence of a Rod-like Structure for Hydroxypropyl Cellulose Samples in Aqueous Solution.

Because hydroxypropyl cellulose (HpC) is a popular polymeric material that forms a liquid crystalline phase in solutions with various kinds of solvents, including water, it is commonly thought that HpC has a typical rod-like structure in solution. In this study, the structures of commercial HpC samples in aqueous solution with average molar substitution numbers (MS) ranging from 3.6 to 3.9 and weight-average molar masses (Mw) ranging from 36 to 740 kg mol-1 were investigated in detail. We first used multiple techniques, including standard static and dynamic light scattering (SLS and DLS), neutron and X-ray scattering experiments, and viscometric measurements, to obtain clear evidence of rod-like structures quantitatively. The dependence of excess scattering intensities for HpC samples under dilute conditions on the magnitude of the scattering vector over a wide range from 8.9 × 10-3 to 3.0 × 10 nm-1 was reasonably described by the form factor of rod particles with length (L) and diameter (d). Although the determined L value was close to the contour length (lc) calculated from the Mw values in the lower Mw range, L became obviously less than lc with increasing Mw. The radius of gyration (Rg) determined via SLS measurements was proportional to L by a factor of approximately 3.5 ∼ √12 over the Mw range examined. These observations revealed that the conformation of HpC molecules changes from an elongated single chain to a certain folded structure, maintaining the shape of the rod-shaped particles. Moreover, the Mw dependencies of the intrinsic viscosities and translational diffusion coefficients of the HpC samples resulting from DLS measurements were reasonably described with a theoretical rod-like particle model, assuming that L and d are identical to those resulting from the scattering behaviors.

Exploring the structural, functional, and biocompatibility aspects of marine bacterial extracellular polysaccharides for biopharmaceutical applications

Marine bacterial extracellular polysaccharides (EPS) represent a unique class of biopolymers with vast potential in biopharmaceutical research due to their diverse structural characteristics, functional properties, and biocompatibility. This study delves into the comprehensive analysis of the monosaccharide composition, molecular weight distribution, and conformational dynamics of marine bacterial EPS, employing advanced analytical techniques such as Nuclear Magnetic Resonance (NMR) spectroscopy, Mass Spectrometry (MS), and Size-Exclusion Chromatography coupled with Multi-Angle Laser Light Scattering (SEC-MALLS). Furthermore, we explore the functional applications of these EPS in biofilm inhibition, immunomodulation, and as innovative drug delivery systems, highlighting their role in enhancing antibiotic efficacy and mitigating resistance. Through quantitative analysis and mathematical modeling, including rheological studies and kinetic modeling of biodegradation, this work assesses the EPSs biocompatibility and biodegradability, essential for their safe use in biomedicine. Our findings underscore the potential of marine bacterial EPS in developing novel biopharmaceutical formulations that are not only effective but also environmentally sustainable and biocompatible, paving the way for future advancements in medical and therapeutic applications.

BaTiO3 Catalyzed Ultrasonic-Driven Piezoelectric-Induced Reversible Addition-Fragmentation Chain-Transfer Polymerization in Aqueous Media.

Compared with normal stimulus such as light and heat, ultrasonic possesses much deeper penetration into tissues and organs and has lower scattering in heterogeneous systems as a noninvasive stimulus. Reversible addition-fragmentation chain-transfer polymerization (RAFT) in aqueous media is performed in a commercial ultrasonic wash bath with 40kHz frequency ultrasonic, in the presence of piezoelectric tetragonal BaTiO3 (BTO) nanoparticles. Owing to the electron transfer from BTO under the ultrasonic action, the water can be decomposed to produce hydroxyl radical (HO•) and initiate the RAFT polymerization (piezo-RAFT). The piezo-RAFT polymerization exhibits features of controllable and livingness, such as linear increase of molar mass and narrow molar mass distributions (Mw/Mn < 1.20). Excellent temporal control of the polymerization and the chain fidelity of polymers are illustrated by "ON and OFF" experiment and chain extension, separately. Moreover, this ultrasonic-driven piezoelectric-induced RAFT polymerization in aqueous media can be directly used for the preparation of piezoelectric hydrogel which have potential application for stress sensor.

Development and attestation of a standard sample of calcium nadroparin

Introduction. The widespread use of heparin preparations for the treatment and prevention of venous thromboembolic complications is known. One of the low molecular weight heparin drugs successfully used in clinical practice is calcium nadroparin. The modern approach to assessing the quality of medicines involves the use of standards, in comparison with which the quality control of the drug is carried out – standard samples (SS). The most important specific parameter in assessing the authenticity of low molecular weight heparins is the characteristic of the fractional composition.Aim. The aim of the work was to develop, attestation and determine the stability during the shelf life of a secondary standard sample to determine the authenticity of calcium nadroparin as part of improving the quality control system of the enterprise with the prospect of creating a domestic pharmacopoeia standard sample.Materials and methods. The object of development and attestation was the standard sample of the enterprise – low molecular weight heparin, obtained on the basis of the Technology implementation center of Siberian state medical university. The certified standard sample was obtained by purification of calcium nadroparin by solid-phase extraction. The completeness of the purification was confirmed by comparing the chromatograms of the purified samples with the chromatograms of the international standard sample. The characteristics of the molecular weight distribution were determined chromatographically. The stability of the certified SSE (the standard sample of the enterprise) was studied under two storage conditions – at a temperature below 8 °C in a dry state for 16 months and in solution at –40 °C for 6 months by evaluating trends in molecular weight distribution.Results and discussion. For each batch of the certified standard sample, the molecular weight and molecular weight characteristics are calculated in 2 parallel definitions, and a representative chromatogram is presented. The values of the relative standard deviation of the molecular weight of the samples and the content of the controlled fractions did not exceed 2.5 %. A detailed analysis of the molecular weight distribution showed the "classical" dependence of RSD (relative standard deviation) from the average value with a significant increase up to 30 % for small fraction values (less than 0.5 %). It was found that during 16 months at a storage temperature below 8 ºC, the molecular weight and molecular weight characteristics of standard samples of low molecular weight heparin did not significantly change. However, in the SSE solution at a storage temperature of minus 40 °C for 6 months, they degraded by more than 10 %.Conclusion. According to the results of the study, a protocol has been developed for obtaining a standard sample of low-molecular-weight heparin for the standardization of the calcium nadroparin substance according to the indicator "molecular weight distribution". The established shelf life of the sample is at least 16 months at temperatures below 8 °C. The stability of solutions of the standard sample at a storage temperature of –40 °C for 3 months is shown.

Electric Field Effect of the Plasma-Initiated Polymerization of Methyl Methacrylate: A Negatively Charged Long-Lived Radical.

Plasma-initiated polymerization (PIP) is generally attributed to a radical process due to its inhibiting property. However, its unique polymerization behaviors like long-lived radical and solvent effect do not comply well with the traditional radical mechanism. Herein, the PIP of methyl methacrylate (MMA) was conducted in a high-voltage DC electric field to investigate the charged nature of its radicals. Consequently, the polymerization presented a preferential distribution of polymers at the anode but not the cathode, revealing the negatively charged nature of the growing radicals. An acceleration phenomenon, accompanied by the growth in molecular weights and the reduction in molecular weight distributions (Ð), was observed at the voltages above 16 kV, suggesting the dissociation of ion pairs of growing radicals. The PIP yielded PMMA with analogous chemical and steric structures to those of PMMA from traditional radical initiation, whether in the presence or absence of the external electric field. This work offers new insights into the PIP of vinyl monomers, wherein a one-electron transfer reaction is inferred to be involved in the monomer activation.

RELAXATION BEHAVIOR OF THREE-DIMENSIONAL PRINTED NBR-BASED RUBBER O-RINGS AS THE INNER PART OF ROD SEALS

ABSTRACT The viscoelastic properties of rubber polymer–based compounds are crucial for further applications but challenging in the manufacturing process using additive manufacturing techniques. The fact that the first layer is attached to the printing bed restricts free relaxation after extrusion and the part shows a strong contraction along the printing direction after release and especially after vulcanization. In this study, the molar mass distribution and the acrylonitrile (ACN) content of an NBR-based compound for the fabrication of O-rings for rod seal applications were varied to demonstrate the different degree of contraction resulting from three-dimensional printing. An ACN content of 34% and an average molar mass of 2.47·105 g·mol−1 with a dispersity index of 2.6 was found to be a suitable compromise between the degree of contraction and compression set as a criterion for the application as O-ring as the inner part of rod seals.

Linking Chemical Structure to the Linear and Nonlinear Properties of Asphalt Binders

The study described in this paper aims to establish the relationship between the chemical composition and rheological properties of asphalt binders in both the linear viscoelastic (LVE) and nonlinear viscoelastic (NLVE) domains. Two asphalt binders with different penetration grades were subjected to four distinct aging treatments of varying severity, resulting in changes in their chemical fingerprints. Chemical characteristics of the asphalt binders were analyzed using thin-layer chromatography (TLC), Fourier Transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). Frequency sweep tests were conducted to evaluate the LVE behavior of the asphalt binders, while multiple stress creep recovery (MSCR) tests were employed to assess their NLVE properties. With regard to the LVE properties, rheological index ( R) and zero shear viscosity (ZSV) derived from the Christensen-Anderson-Marasteanu (CAM) model exhibited high correlations with FTIR and molecular weight distribution (MWD) parameters. Additionally, the polydispersity index (PDI) displayed a stronger correlation with LVE-based parameters. Findings from the MSCR tests revealed that the sensitivity of the percentage recovery ( %R) to chemical composition, as opposed to nonrecoverable creep compliance ( Jnr), can be largely attributed to the degree of nonlinearity. Furthermore, it was observed that lower molecular weight molecules exert a greater influence on %R in the nonlinear domain. Finally, it was found that Jnrslope is a more reliable parameter than Jnrdiff for assessing the effects of chemical makeup on stress and temperature sensitivity.