The structural evolution of high-density polyethylene during crazing in liquid medium

Modification of High-Density Polyethylene with a Fibrillar-Porous Structure by Biocompatible Polyvinyl Alcohol via Environmental Crazing

Polymer/polymer nanocomposites based on high-density polyethylene (HDPE) and biocompatible polyvinyl alcohol (PVA) were prepared by tensile drawing of HDPE in the PVA solutions via environmental crazing. The mechanism of this phenomenon was described. The HDPE/PVA nanocomposites were studied by the methods of scanning electron microscopy, atomic force microscopy, gravimetry, tensile tests, and their composition, properties, and performance were characterized. The content of PVA in the HDPE/PVA nanocomposites (up to 22 wt.%) was controlled by the tensile strain of HDPE and concentration of PVA in the solution. Depending on the content of PVA, the wettability of the HDPE/PVA nanocomposite (hydrophilic-lipophilic balance) could be varied in a broad interval from 45 to 98°. The modification of HDPE by the biocompatible PVA offers a beneficial avenue for practical applications of the HDPE/PVA composites as biomedical materials, packaging and protective materials, modern textile articles, breathable materials, membranes and sorbents, etc.

Nanocomposite Materials Based on Polylactide and Gold Complex Compounds for Absorbed Dose Diagnostics in BNCT

In this study, approaches to the synthesis of complex compound of gold with cysteine [AuCys]n for measuring absorbed dose in boron neutron capture therapy (BNCT) were developed. The dependence of the complex particle size on pH were established. Nanocomposite materials based on polylactide containing [AuCys]n particles with an average size of about 20 nm were obtained using the crazing mechanism. The structure of obtained materials was studied by electron microscopy. The release kinetics of [AuCys]n from polymer matrix were investigated. Release of [AuCys]n from the volume of the polymeric matrix had a delayed start-this process began only after 24 h and was characterized by an effective rate constant of 1 μg/h from a 20 mg composite sample. At the same time, in vitro studies showed that the concentration of 6.25 μg/mL was reliably safe and did not reduce the survival of U251 and SW-620 cells.

Functionalization and Surface Modification of Mesoporous Hydrophobic Membranes by Oligomers and Target Additives via Environmental Crazing

This work offers an ecologically friendly and facile approach for the modification of high-tonnage commercial polymers, including polypropylene (PP), high-density polyethylene (HDPE), and poly(ethylene terephthalate) (PET), and preparation of nanocomposite polymeric membranes via incorporation of modifying oligomer hydrophilic additives, such as poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), polyvinyl alcohol (PVA), and salicylic acid (SA). Structural modification is accomplished via the deformation of polymers in PEG, PPG, and water-ethanol solutions of PVA and SA when mesoporous membranes are loaded with oligomers and target additives. The content of target additives in nanocomposite membranes is controlled by tensile strain, and the level of loading can achieve 35-62 wt.% for PEG and PPG; the content of PVA and SA is controlled by their concentration in the feed solution. This approach allows for the simultaneous incorporation of several additives which are shown to preserve their functional performance in the polymeric membranes and their functionalization. The porosity, morphology, and mechanical characteristics of the prepared membranes were studied. The proposed approach allows an efficient and facile strategy for the surface modification of hydrophobic mesoporous membranes: depending on the nature and content of target additives, their water contact angle can be reduced to 30-65°. Water vapor permeability, gas selectivity, antibacterial, and functional properties of the nanocomposite polymeric membranes were described.

Current State-of-the-Art in Membrane Formation from Ultra-High Molecular Weight Polyethylene

One of the materials that attracts attention as a potential material for membrane formation is ultrahigh molecular weight polyethylene (UHMWPE). One potential material for membrane formation is ultrahigh molecular weight polyethylene (UHMWPE). The present review summarizes the results of studies carried out over the last 30 years in the field of preparation, modification and structure and property control of membranes made from ultrahigh molecular weight polyethylene. The review also presents a classification of the methods of membrane formation from this polymer and analyzes the conventional (based on the analysis of incomplete phase diagrams) and alternative (based on the analysis of phase diagrams supplemented by a boundary line reflecting the polymer swelling degree dependence on temperature) physicochemical concepts of the thermally induced phase separation (TIPS) method used to prepare UHMWPE membranes. It also considers the main ways to control the structure and properties of UHMWPE membranes obtained by TIPS and the original variations of this method. This review discusses the current challenges in UHMWPE membrane formation, such as the preparation of a homogeneous solution and membrane shrinkage. Finally, the article speculates about the modification and application of UHMWPE membranes and further development prospects. Thus, this paper summarizes the achievements in all aspects of UHMWPE membrane studies.

The Aging Performance of PVDF in Acid Oil and Gas Medium

In the process of transporting oil and gas, the service performance of thermoplastic pipes will decline due to the multiple influences of medium, temperature, and pressure. In order to study the service performance changes of PVDF pipes under oil and gas transportation conditions, the high-temperature autoclave is used to simulate the service state of the pipe in the mediums. The PVDF samples are exposed to simulated oil and gas mediums for 1 week, 3 weeks, 5 weeks, and 7 weeks under 60 °C and 90 °C conditions. After the exposure test, the physical and chemical properties of the PVDF pipe are tested and compared with the initial samples. Compared with the initial sample, the sample quality after the exposure test has a slight increase, with growth rates of 2% and 3% at 60 °C and 90 °C, respectively. Meanwhile, the tensile strength of the samples is about 13% and 21% lower than that of the initial sample, respectively. According to the microscopic morphology analyses, there are some crack defects on the surface of the sample after the exposure test. Through infrared analysis, it is shown that no molecular chain breakage, crosslinking, or other reactions are found after the exposure test. The above analysis shows that the PVDF sample has slight penetration and swelling during the exposure test. However, due to the large force between the PVDF molecules, its mechanical properties have a small downward trend, showing excellent environmental stress crack resistance.

Environmental Stress Cracking of High-Density Polyethylene Applying Linear Elastic Fracture Mechanics

The crack propagation rate of environmental stress cracking was studied on high-density polyethylene compact tension specimens under static loading. Selected environmental liquids are distilled water, 2 wt% aqueous Arkopal N100 solution, and two model liquid mixtures, one based on solvents and one on detergents, representing stress cracking test liquids for commercial crop protection products. The different surface tensions and solubilities, which affect the energetic facilitation of void nucleation and craze development, are studied. Crack growth in surface-active media is strongly accelerated as the solvents induce plasticization, followed by strong blunting significantly retarding both crack initiation and crack propagation. The crack propagation rate for static load as a function of the stress intensity factor within all environments is found to follow the Paris–Erdogan law. Scanning electron micrographs of the fracture surface highlight more pronounced structures with both extensive degrees of plasticization and reduced crack propagation rate, addressing the distinct creep behavior of fibrils. Additionally, the limitations of linear elastic fracture mechanisms for visco-elastic polymers exposed to environmental liquids are discussed.

Cold Crystallization of Glassy Polylactide during Solvent Crazing

Uniaxial tension accompanied by the orientation and crystallization of polymer chains is one of the powerful methods for the improvement of mechanical properties. Crystallization of amorphous isotropic polylactide (PLA) at room temperature is studied for the first time during the drawing of films in the presence of liquid adsorption-active media (ethanol, water-ethanol mixtures, and n-heptane) by the solvent crazing mechanism. The crystalline structure arises only under simultaneous actions of a liquid medium and a tensile stress and does not depend on the nature of the environment. The degree of polymer crystallinity increases nearly linearly with the growth in the fraction of the fibrillar material and reaches a maximum value of 42-45%. It has been stated that polymer crystallization happens in crazes involving nanofibrils with a diameter of about 10-20 nm without affecting the bulk polymer parts. Wide-angle X-ray scattering has been used to confirm that the crazing-induced crystallization is accompanied by the formation of the α'-crystalline phase with crystallite sizes (X-ray coherent scattering region) of 3-5 nm, depending on the nature of the liquid medium. After stretching in liquid media to a high tensile strain, the strength of a PLA film has increased to 200 MPa.

Micromechanical anisotropy and heterogeneity of the meniscus extracellular matrix

To understand how the complex biomechanical functions of the meniscus are endowed by the nanostructure of its extracellular matrix (ECM), we studied the anisotropy and heterogeneity in the micromechanical properties of the meniscus ECM. We used atomic force microscopy (AFM) to quantify the time-dependent mechanical properties of juvenile bovine meniscus at deformation length scales corresponding to the diameters of collagen fibrils. At this scale, anisotropy in the elastic modulus of the circumferential fibers, the major ECM structural unit, can be attributed to differences in fibril deformation modes: uncrimping when normal to the fiber axis, and laterally constrained compression when parallel to the fiber axis. Heterogeneity among different structural units is mainly associated with their variations in microscale fiber orientation, while heterogeneity across anatomical zones is due to alterations in collagen fibril diameter and alignment at the nanoscale. Unlike the elastic modulus, the time-dependent properties are more homogeneous and isotropic throughout the ECM. These results enable a detailed understanding of the meniscus structure-mechanics at the nanoscale, and can serve as a benchmark for understanding meniscus biomechanical functions, documenting disease progression and designing tissue repair strategies.

STATEMENT OF SIGNIFICANCE

Meniscal damage is a common cause of joint injury, which can lead to the development of post-traumatic osteoarthritis among young adults. Restoration of meniscus function requires repairing its highly heterogeneous and complex extracellular matrix. Employing AFM, this study quantifies the anisotropic and heterogeneous features of the meniscus ECM structure and mechanics. The micromechanical properties are interpreted within the context of the collagen fibril nanostructure and its variation with tissue anatomical locations. These results provide a fundamental structure-mechanics knowledge benchmark, against which, repair and regeneration strategies can be developed and evaluated with respect to the specialized structural and functional complexity of the native tissue.