Journal of Polymer Research最新文献

The use of natural fibers for reinforcing with polymers has grown in popularity over the last few decades. In addition to being lightweight and robust, natural fibers are also reasonably priced. An investigation was carried out in this research work to use human hair fiber, a natural fiber easily available in India. The current research focuses on developing of new class natural fiber-based polymer composites with human hair as reinforcement and vinyl ester as the matrix material. The composite was prepared using the land lay up technique with varied human fiber concentration of 5,10,15,20 & 25 wt %. The prepared composites were tested for their mechanical properties and chemical resistance and results were reported. A highest tensile strength of 56.3 MPa was achieved with 20 wt % of humar fiber content and maximum flexural and impact strength of 1.49 MPa and 37.1 J were attained with 15 wt % of human fiber reinforcement. In the view of chemical properties, among the various chemical solutions, Hydrochloric Acid shows the least weight loss at 0.42%. The SEM analysis shows the void formation, fiber break out, fiber pull out and crack propagation, specifying understandings into the human fiber/vinyl ester composites failure mechanisms.

Hydrazide-substituted phthalonitrile resin (1e) has been synthesized via nucleophilic substitution reaction of hydrazide-substituted bisphenol (1d) with 4-nitrophthalonitrile to introduce a flexible linking group between rings for low-melting material. The resin was molecularly designed with two flexible hinges of hydrazide functionality with an arm and a low melting point resin system. The resin monomer in Differential scanning calorimetry (DSC) analysis, instead of showing a low melting point, showed a relatively high melting peak (T_m) at 266 °C, due to the formation of a more stable enol form on account of an extended conjugation, which was confirmed by Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FTIR), and Ultraviolet (UV) spectra. The monomer was assessed for its thermal, rheological, and curing characteristics. The DSC analysis of uncured 1e showed the onset of curing (T_ons) at 269 °C along with curing window of 69 °C. The processing window was found to be _~40 °C by rheological tests. The enthalpy of curing for 1e was found to be 151.5 Jg⁻¹. Thermogravimetric analysis (TGA) of the fully cured polymer (1f) revealed the onset of thermal degradation (T_do) of 450 °C along with a char yield of 66 wt.% at 800 °C in N₂ atmosphere. In air atmosphere multistep degradation was obtained and nil ash yield was found at 600 °C. The limiting oxygen index (LOI) value of the cured polymer (1f) was found to be ̴ 43.9 (estimated by Krevelen’s equation).

This study investigates the effect of impregnation of graphene oxide (GO) on the acoustic durability of polyurethane (PU) foam. PU foam was impregnated with GO using a vacuum-assisted process. Subsequently, accelerated-aging tests were performed on pristine and GO-impregnated PU. Assessments of the transport parameters and absorption coefficients indicated that impregnation with GO enhances the acoustic durability of the PU foams. While pristine PU experienced notable changes in acoustic behavior owing to thermal aging, the GO-impregnated foam exhibited substantial inhibition of changes in transport parameters and absorption coefficients, especially with higher GO content. To investigate the mechanisms of these phenomena, the morphologies of the foams were examined using scanning electron microscopy. Pristine PU exhibited an increased opening ratio as a consequence of thermal aging, resulting from the destruction of cell membranes between the pores. Conversely, the GO-impregnated PU foam remained stable against these changes because the GO filled the open pores within the porous structure. Our results underscore the ability of GO impregnation to ameliorate the thermal aging-induced deterioration of the acoustic properties of PU foams. This study presents valuable insights for enhancing the acoustic durability of PU foams in applications where sound absorption is of paramount importance.

Flax Fibers (FF) and Ramie Fibers (RF), with equal holo-cellulose contents (approx. 87%), have been used in equal proportions as reinforcements to develop their Chemically Functionalized Polypropylene (CF-PP) hybrid composites: [5/5]/90, [10/10]/80 and [15/15]/70 [FF/RF]/CF-PP hybrid composites. These hybrid composites, developed by extrusion followed by injection molding, exhibit good adhesion of FF and RF with CF-PP, as evident in their FE-SEM micrographs. FTIR establishes this adhesion originating from ester bonds and hydrogen bonds, formed between the reinforcements and the matrix by Palsule process. These [FF/RF]/CF-PP hybrid composites display higher tensile, flexural and impact properties than their matrix, and the property values increase proportionally with the total reinforcement content in the hybrid composites. Of all the hybrid composites, the [15/15]/70 [FF/RF]/CF-PP composite exhibits the highest mechanical properties, likely due to the highest total reinforcement content. Water absorption by the composites increases with the reinforcement content, and the [15/15]/70 composition shows the highest water uptake. Relative to the synthetic and inorganic fiber based composites, these [FF/RF]/CF-PP hybrid composites offer relatively better life cycle assessment parameters and higher sustainability with potential for reduced adverse impacts of environmental and energy during their manufacturing and applications.

To address growing concerns regarding the endocrine-disrupting effects of traditional phthalate plasticizers (PAEs), this study synthesized three novel cycloalkyl tetra-ester compounds (1c, 2d, and 3d) as sustainable alternatives, utilizing readily available dicyclopentadiene (DCPD) as a precursor. PVC formulations incorporating 50 wt % of compound 3d exhibited enhanced tensile strengths (24.5 MPa) and improved thermal stability (T5% = 213.5 °C) compared to dioctyl phthalate (DOP; 22.2 MPa and 191.3 °C, respectively). The optimized molecular geometry suggests that the multi-cyclic and bridged structures, along with the four interlocked alkyl groups of the synthesized compounds, enhance their interactions with polymer chains, thereby increasing resistance to volatilization and ethanol extraction in PVC. However, these structural features also restrict the mobility of the polymer chains, resulting in reduced elongation and a higher glass transition temperature, particularly for the tricyclic compound 3d. All synthesized compounds displayed less than 5% of the estrogen receptor binding affinity of DOP, suggesting negligible endocrine-disrupting effects. These cost-effective, DCPD-derived compounds show promise as eco-friendly alternatives to PAEs, particularly in applications requiring stringent environmental and health standards, such as infant products and food packaging.

The inclusion of bio-fillers to develop a newer material to satisfy the needs of the sustainability agenda is a prime strategy followed by the research communities in recent days. In connection with this, the current work is on the utilization of Teff seed coat powder as an efficient reinforcement in epoxy composites. The open casting method was followed to cast four different proportions of teff powder reinforcement like 2.5, 5, 7.5 and 10% along with neat epoxy. The structural and thermal integrity of the material was investigated with tensile, compressive and thermogravimetric analyses. The density analysis explored the decrement trend in density for the increased content of teff particles. An epoxy composite reinforced with 7.5% teff powder claims to be an exceptional candidate for structural applications with improved properties than other variants. Composites of all compositions have 57% to 130% higher modulus and 39% to 70% higher strength than neat epoxy. Scanning electron micrographs are utilized to understand the structure–property relationships. TG/DTG studies showed that adding teff husk did not affect maximum degradation temperature, but the development of char enhanced the initial degradation temperature accomplished when compared to pristine composites.

Researchers are trying to expand the efficiency and application of shape memory polymers by investigating different parameters on the matrix and additives. This study aims to enhance the physical characteristics by examining the addition of 5%, 10, 20, 30, and 40 wt.% metal oxide Dy₂O₃ nanoparticles into blended poly(lactic acid) (PLA)/polyhydroxyalkanoate (PHA) polymer. The degree of crystallinity, chemical structure, thermal characteristics, magnetic behavior, surface morphology, and mechanical characterizations were studied using XRD, FTIR, DSC, TGA, VSM, SEM, and tensile test. This study identified that the use of Dy₂O₃ nanoparticles in the blend increased the glass transition and melting temperatures, while the enthalpy changes and specific heat capacity of the polymer nanocomposite stayed almost constant. The presence of new interfaces between Dy₂O₃ and the polymer chains was confirmed by FTIR analysis, and the dispersion of the NPs in the polymer matrix was confirmed by SEM analysis. TGA findings proved the enhancement of thermal stability with mass loss of less than 10% at temperatures below 150 ℃. Moreover, the magnetization vs magnetic strength exhibited the paramagnetic behavior of the blend and nanocomposites where the response to the external magnetic field has a direct correlation with the quantity of the additive nanoparticles in the polymer blend. The same improvement has been detected in the mechanical behavior. The elastic modulus of the nanocomposite increased and the samples with more embedded NPs recorded a higher maximum stress. The presence of Dy₂O₃ nanoparticles in PLA/PHA blends impacts the thermal and magnetic properties of the nanocomposite.

Urease enzyme activity can be related to various issues, both in biological systems and in industrial processes. A significant breakthrough in addressing the challenge to maintain enzymatic activity involves the development of enzyme-polymer based bioconjugates. This entails the utilization of dual responsive polymer matrix involving pH-responsive polymer (2-acrylamido-2-methylpropane sulfonic acid (AMPS)), neutral polymer (N, N-dimethylacrylamide (DMA)), temperature-responsive polymer (N-isopropylacrylamide (NIPAM)), and urease derivative (UD) collectively known as [PAMPS-co-PDMA-co-PUD]-b-PNIPAM (ADUN) centered on the RAFT-Grafting through polymerization process. Kinetic assessments, including a comparative study between the free enzyme and urease linked in ADUN, were conducted using berthelot reagents at different pH and temperature levels. The Lineweaver–Burk plot was used to ascertain the Michaelis–Menten kinetic constant (Km) values, which unveiled strikingly similar Km values for the free enzyme and ADUN. This indicates that urease remains active for over a month when stored at room temperature and up to around 70 °C in the case of ADUN, while it becomes dormant in the case of free urease. The microenvironment of the bioconjugates remains intact for urease in acidic pH conditions and at temperatures ranging from mild to high, when the concentration exceeds the critical micelle concentration (CMC). In general, this approach highlights the prolonged durability and commercial adaptability of ADUN for wider uses.

There is an increasing demand for polyimide-based conductive composite materials with excellent mechanical properties and good thermostability for engineering and biomedical applications. A strategy has been proposed to produce composites based on polyimide matrices of various rigidities filled with graphene particles. The results of dynamic mechanical analysis demonstrate that the values of glass transition temperature and elastic modulus of these composites increase (from 3.1 GPa to 9.6 GPa) with increasing rigidity of the PI matrix. An increase in the PI rigidity also leads to a decrease in volume conductivity of samples (from 10^–4 to 5 × 10^–7 S/m), while their surface conductivity increases (from 0.04 S/m to 2 S/m). Apparently, this is due to expulsion of graphene into the near-surface area of the composite film, which is confirmed by independent methods (X-ray photoelectron spectroscopy and IR spectroscopy). The macromolecules of rigid-chain polyimide demonstrate planar orientation, which facilitates the appearance of strong π–π-interactions between monomer units of polymer chains and prevents uniform distribution of graphene particles within the volume of this polyimide matrix.