Review: Crystallization of Biodegradable Polymers

Understanding the crystallization behavior of polymer is significant both theoretically and practically as it decides the microscopic structure of polymer and determines final physical properties of the product. This article provides deep insight into the process of crystallization by exploring various models proposed for crystallization, factors determining crystallization, thermodynamics and kinetics in detail. The correlation of crystallinity with various properties is also discussed. For kinetics evaluation, the basic hypotheses of various models, as well as their relative drawbacks are also underlined. This article also reviews the crystallization behavior of widely useful biodegradable polymers such as poly(?-caprolactone) and poly(lactic acid).     

Influence of aspect ratio of fillers on the properties of acrylonitrile butadiene styrene composites

Aspect ratio (shape) of the filler is one of the key factors which play a vital role in determining the properties of the composites. Fillers like talc and calcium carbonate (CaCO₃) have different aspect ratios and affect the properties differently. This study was carried out to investigate the effect of aspect ratio of the filler on the properties of the acrylonitrile butadiene styrene (ABS) polymer. The rheological, mechanical, thermal properties, and fracture morphology were studied for the ABS composites filled with talc and CaCO₃ at various filler loading. Coupling agent was added to improve the interfacial adhesion between the filler and the ABS matrix. The aspect ratio of fillers affected the flow behavior at lower shear rate, and was insignificant at higher shear rates. The flow‐induced morphology was more effective in case of talc giving a significant increase in the bending modulus. Tensile and flexural strength showed a slight decrease in the values with talc showing better performance as compared to CaCO₃. The reverse was observed in case of impact strength, with CaCO₃ showing lower drop in the values. Aspect ratio of filler had no significant effect on the thermal properties of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46023.     

Preparation of acylated microcrystalline cellulose using olive oil and its reinforcing effect on poly(lactic acid) films for packaging application

A novel poly(lactic acid) (PLA) based composite, reinforced by microcrystalline cellulose (MCC) was prepared. MCC was modified by esterification reaction using olive oil for improving the compatibility with PLA matrix. The acylated microcrystalline cellulose (AMCC) exhibited reduced polarity in comparison to unmodified MCC. AMCC/ PLA composite films were prepared using solvent casting technique. The effects of the MCC surface modification on morphological, mechanical, physical, thermal, biodegradability and barrier properties of the PLA based MCC composites were studied. FTIR analysis confirmed acylation reaction of MCC. Scanning electron microscopy analysis exhibited a uniform distribution of AMCC in PLA matrix. Barrier properties of AMCC based composites were improved as compared to MCC based composites. The tensile strength and tensile modulus of composite films (at 2 wt.% AMCC) were improved about 13% and 35% as much as those of the pure PLA films, respectively. These biodegradable composite films can be a sustainable utilization of olive oil and microcrystalline cellulose in the food packaging application.     

Beyond parameter estimation: extending biomechanical modeling by the explicit exploration of model topology

Selecting a model topology that realistically predicts biomechanical function remains an unsolved problem. Today's dominant modeling approach is to replicate experimental input/output data by performing parameter estimation on an assumed topology. In contrast, we propose that modeling some complex biomechanical systems requires the explicit and simultaneous exploration of model topology (i.e., the type, number, and organization of physics-based functional building blocks) and parameter values. In this paper, we use the example of modeling the notoriously complex tendon networks of the fingers to present three critical advances towards the goal of implementing this extended modeling paradigm. First, we describe a novel computational environment to perform quasi-static simulations of arbitrary topologies of elastic structures undergoing large deformations. Second, we use this form of simulation to show that the assumed topology for the tendon network of a finger plays an important role in the propagation of tension to the finger joints. Third, we demonstrate the use of a novel inference algorithm that simultaneously explores the topology and parameter values for hidden synthetic tendon networks. We conclude by discussing critical issues of observability, separability, and uniqueness of topological features inferred from input/output data, and outline the challenges that need to be overcome to apply this novel modeling paradigm to extract causal models in real anatomical systems.     

Edible mushrooms: The potential game changer in alleviating vitamin D deficiency and improving human health

The present review attempts to critically examine and evaluate research findings on mushrooms as sources of vitamin D and other nutraceuticals. Recently, there is a growing concern about diseases associated with the deficiency of vitamin D in humans. As people tend to stay indoors, in present times, due to the COVID-19 pandemic, vitamin D levels are further affected. Research indicates vitamin D as a promising defensive or therapeutic agent against COVID, making this review more crucial. Mushrooms, as a rich source of vitamin D along with various bioactive compounds, perform a significant role in resolving health issues. Robust analyses of various strategies for enhancing vitamin D content in mushrooms holds significance in this study; moreover, this will help stakeholders of the mushroom industry in enriching the overall mushroom quality and human health. Mushroom-based medicinal formulations and functional foods serve to deliver vitamins and nutrients to humans, thus helping to combat malnutrition and other health problems, especially in developing countries. Evidence from pre-clinical and clinical analyses suggests that vitamin D₂ bioavailability in mushrooms is comparable with vitamin D from other sources. The review also emphasises molecular findings from mushrooms related to genes responsible for morphology and metabolic production of pro-vitamin-D₂.     

A novel approach for prediction of surface roughness in turning of EN353 steel by RVR-PSO using selected features of VMD along with cutting parameters

The abrupt changes in tool-workpiece interaction during machining process induce variation in the surface quality of work material. These interactions include built-up edge formation and their break-off, environmental conditions (use of coolant, rise of temperature etc.), material imperfections, improper structural fitness of machine & tool components, etc. This study presents prediction of surface roughness in turning of EN353 steel implementing the variational mode decomposition (VMD) for processing the vibration data, followed by estimation of the surface roughness using the relevance vector regression (RVR) optimized by particle swarm optimization (PSO). The raw vibration data has been decomposed in five discrete sets of frequency components known as variational mode functions (VMFs). A set of twenty-one statistical features in each three axes have been extracted for raw data and each VMF. The RVR has been trained using these 21×3 = 63 features and 3 cutting parameters — cutting speed, feed depth of cut. The RVR has also been trained separately using top 5 features selected through RreliefF algorithm. The optimal decomposition level has been determined to minimize the noise and predict the surface finish accurately. The results obtained in 1st VMF (high frequency, low amplitude) using its top 5 features for prediction have been found to be reliable with higher prediction accuracy.

     

Filament Nucleation Tunes Mechanical Memory in Active Polymer Networks

Incorporating growth into contemporary material functionality presents a grand challenge in materials design. The F‐actin cytoskeleton is an active polymer network that serves as the mechanical scaffolding for eukaryotic cells, growing and remodeling in order to determine changes in cell shape. Nucleated from the membrane, filaments polymerize and grow into a dense network whose dynamics of assembly and disassembly, or “turnover,” coordinates both fluidity and rigidity. Here, the extent of F‐actin nucleation is varied from a membrane surface in a biomimetic model of the cytoskeleton constructed from purified protein. It is found that nucleation of F‐actin mediates the accumulation and dissipation of polymerization‐induced F‐actin bending energy. At high and low nucleation, bending energies are low and easily relaxed yielding an isotropic material. However, at an intermediate critical nucleation, stresses are not relaxed by turnover and the internal energy accumulates 100‐fold. In this case, high filament curvatures template further assembly of F‐actin, driving the formation and stabilization of vortex‐like topological defects. Thus, nucleation coordinates mechanical and chemical timescales to encode shape memory into active materials.     

Synthesis,characterization and antimicrobial activity of transition metal chelated thiourea‐formaldehyde resin

A polymeric ligand (thiourea‐formaldehyde resin ‐ TUFR) bearing nitrogen and sulfur donor groups was synthesized by the polycondensation of thiourea and formaldehyde in acidic medium and its polychelates were prepared in alcoholic solution of metal ions such as Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). The TUFR polymeric ligand and its TUFR‐M(II) polychelates were characterized with micro‐analytical analysis and spectral studies. The FTIR spectra of polychelates indicated that the metal ions were coordinated through the sulfur of the thionyl (C?S) groups and formed a covalent bond with the nitrogen of the NH groups. Electronic spectra, electronic spin resonance (ESR) spectra and magnetic moments revealed that the polychelates of Mn(II), Co(II) and Ni(II) were octahedral; however, Cu(II) and Zn(II) polychelates were square‐planar and tetrahedral, respectively. The thermogravimetric analysis data indicated that the polychelates were more stable than the corresponding ligand. The antimicrobial activities of all the compounds against several bacteria and fungi were also investigated by using the agar well diffusion method. Copyright © 2006 Society of Chemical Industry     

An accumulative error based adaptive design of experiments for offline metamodeling

A popular method to reduce the computational effort in simulation-based engineering design is by way of approximation. An approximation method involves two steps: Design of Experiments (DOE) and metamodeling. In this paper, a new DOE approach is introduced. The proposed approach is adaptive and samples more design points in regions where the simulation response is expected to be highly nonlinear and multi-modal. Numerical and engineering examples are used to demonstrate the applicability of the proposed DOE approach. The results from these examples show that for the same number of simulation evaluations and according to metamodel accuracy, the proposed DOE approach performs better for majority of test examples compared to two previous methods, i.e., the maximum entropy design method and maximum scaled distance method.