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The ability to quickly develop predictions of the service lifetime of plastic pipes at different load levels allows designers to choose the best plastic material and design pipe for a specific application. Additionally, it helps material producers to rapidly design, manufacture, test, screen, and modify the base polymeric material. The aim of this study is to introduce a combined experimental and analytical framework to develop accelerated lifetime estimates for semi-crystalline plastic pipes which is sensitive to the structure, orientation, and morphology changes introduced by changing processing conditions. To accomplish this task, high density polyethylene (HDPE) is chosen as the exemplary base material and custom fixtures are developed to admit tensile and hoop burst tests on the as-manufactured HDPE pipes. A pressure-modified Eyring flow equation is employed to predict the rupture lifetime of HDPE pipes using the measured mechanical properties under uniaxial tensile and compression loading in different temperatures and strain rates. The method allows the prediction of pipe service lifetimes in excess of 50 years using experiments conducted over approximately 10 days instead of the traditional 13 months., INTRODUCTION The use of plastic pipes to carry liquids and gases has greatly expanded in recent decades because of their moderate cost, ease of handling and installation, long service life, [...]

Poly(ether ether ketone) (PEEK) was found to form gels in the benign solvent 1,3-diphenylacetone (DPA). Gelation of PEEK in DPA was found to form an interconnected, strut-like morphology composed of polymer axialites. To our knowledge, this is the first report of a strut-like morphology for PEEK aerogels. PEEK/DPA gels were prepared by first dissolving PEEK in DPA at 320 °C. Upon cooling to 50 °C, PEEK crystallizes and forms a gel in DPA. The PEEK/DPA phase diagram indicated that phase separation occurs by solid–liquid phase separation, implying that DPA is a good solvent for PEEK. The Flory–Huggins interaction parameter, calculated as χ12 = 0.093 for the PEEK/DPA system, confirmed that DPA is a good solvent for PEEK. PEEK aerogels were prepared by solvent exchanging DPA to water then freeze-drying. PEEK aerogels were found to have densities between 0.09 and 0.25 g/cm3, porosities between 80 and 93%, and surface areas between 200 and 225 m2/g, depending on the initial gel concentration. Using nitrogen adsorption analyses, PEEK aerogels were found to be mesoporous adsorbents, with mesopore sizes of about 8 nm, which formed between stacks of platelike crystalline lamellae. Scanning electron microscopy and X-ray scattering were utilized to elucidate the hierarchical structure of the PEEK aerogels. Morphological analysis found that the PEEK/DPA gels were composed of a highly nucleated network of PEEK axialites (i.e., aggregates of stacked crystalline lamellae). The highly connected axialite network imparted robust mechanical properties on PEEK aerogels, which were found to densify less upon freeze-drying than globular PEEK aerogel counterparts gelled from dichloroacetic acid (DCA) or 4-chlorphenol (4CP). PEEK aerogels formed from DPA were also found to have a modulus–density scaling that was far more efficient in supporting loads than the poorly connected aerogels formed from PEEK/DCA or PEEK/4CP solutions. The strut-like morphology in these new PEEK aerogels also significantly improved the modulus to a degree that is comparable to high-performance crosslinked aerogels based on polyimide and polyurea of comparable densities. [ABSTRACT FROM AUTHOR]

This study proposes a novel method to mechanically characterize the performance of individual bonds in low-density, thermomechanically bonded nonwoven fabrics. Commercial bicomponent, polyethylene/polypropylene (PE/PP), nonwoven fabric was laser cut into bowtie-shaped specimens for uniaxial tensile testing so that the central region of each specimen contained an individual bond. Three groups, each composed of 20 specimens, were tested with their longitudinal axes oriented along the machine direction (MD), the cross direction (CD), and at 45[degrees] between these two directions (DD). Prior to testing, the intrinsic variation in areal density and fiber orientation in the region surrounding the individual bond were quantified via orientation and relative basis weight parameters. During testing, images of the specimens were acquired to determine the occurrence of fiber breakage, bond deformation, and bond cohesive failure. Maximum force, stiffness, and orientation parameters were found to be significantly different among the three specimen groups (p < 0.01) but the relative basis weight was not (p> 0.01). The stiffness and maximum load were linearly correlated with both the areal density and fiber orientation. Preexisting voids or windows within the bond lowered the maximum force for specimens with the longitudinal axes aligned with the MD. These voids had no influence on the maximum force achieved by the specimens aligned with the CD and DD. The bonds in these specimens were observed to deform less than the bonds in the specimens with the longitudinal axes aligned with the MD. The results indicate the importance of the fiber structure surrounding the bond on the tensile properties, deformation and failure mode of individual bonds within the nonwoven fabric., INTRODUCTION The global market for spunbond nonwoven fabrics is growing rapidly and expected to reach over $50 billion by 2020 [1]. This growth can be attributed to nonwoven's numerous applications, [...]

This manuscript describes the synthesis and characterization of guanine and cytosine‐containing supramolecular copolymers, which are inspired from the guanine and cytosine nucleobase pair in deoxyribonucleic acid. Regioselective Michael‐addition allowed the efficient installation of the nucleobases on acrylate‐containing monomers, which enabled the preparation of a series of nucleobase‐functionalized acrylate and n‐butyl acrylate copolymers using conventional free radical copolymerization. Guanine‐containing copolymers exhibited superior thermal properties, thermomechanical performance, and more defined morphological structure than cytosine‐containing copolymer analogs due to the relatively strong guanine self‐association, thus expanding the potential applications for mechanically reinforced polymeric networks. Blending guanine‐ and cytosine‐containing copolymers formed a supramolecular structure through multiple hydrogen bonding between guanine and cytosine units. The supramolecular blend exhibited intermediate thermomechanical and morphological properties, which suggested that guanine and cytosine units were not fully associated in the random copolymer composition. This work provides valuable fundamental understanding of structure–property‐morphology relationships in acrylic copolymers with the presence of guanine‐cytosine self‐ and complementary interactions, suggesting new understanding in supramolecular design for enhanced mechanical and morphological properties. [ABSTRACT FROM AUTHOR]

In an effort to synthesize chemically recyclable thermoplastic elastomers, a redox‐switchable catalytic system was developed to synthesize triblock copolymers containing stiff poly(lactic acid) (PLA) end blocks and a flexible poly(tetrahydrofuran‐co‐cyclohexene oxide) (poly(THF‐co‐CHO) copolymer as the mid‐block. The orthogonal reactivity induced by changing the oxidation state of the iron‐based catalyst enabled the synthesis of the triblock copolymers in a single reaction flask from a mixture of monomers. The triblock copolymers demonstrated improved flexibility compared to poly(l‐lactic acid) (PLLA) and thermomechanical properties that resemble thermoplastic elastomers, including a rubbery plateau in the range of −60 to 40 °C. The triblock copolymers containing a higher percentage of THF versus CHO were more flexible, and a blend of triblock copolymers containing PLLA and poly(d‐lactic acid) (PDLA) end‐blocks resulted in a stereocomplex that further increased polymer flexibility. Besides the low cost of lactide and THF, the sustainability of this new class of triblock copolymers was also supported by their depolymerization, which was achieved by exposing the copolymers sequentially to FeCl3 and ZnCl2/PEG under reactive distillation conditions. [ABSTRACT FROM AUTHOR]

An array of perfectly alternating polycarbonate-polydimethylsiloxane (PC-PDMS) multiblock copolymers possessing systematic variations in block molecular weights were successfully produced by coupling preformed PC and PDMS telechelic oligomers using hydrosilylation. Based on gel permeation chromatography results, the multiblock copolymers were essentially void of the oligomeric precursors. Despite the relatively large difference in solubility parameter between PC and PDMS, the multiblock copolymers exhibited significant partial miscibility between the two phases. As expected, the degree of partial miscibility was dependent on the molecular weight of the blocks with the extent of partial miscibility increasing with decreasing block molecular weights. Morphological characterization using small angle X-ray scattering showed that, at a given PC block molecular weight, the uniformity of the two phase morphology increased with increasing PDMS block molecular weight, which is consistent with a decrease in the extent of phase mixing with increasing PDMS block molecular weight., INTRODUCTION Because of their ability to produce highly ordered and tuneable nanoscale morphologies through self-assembly, block copolymers have become a very important class of materials. Depending on compositional variables, such [...]