A comparison of the strength of autohesion of plasma treated amorphous and semi‐crystalline PEEK films

Polyether ether ketone (PEEK) is a promising material for the encapsulation of electronic components for medical implants but a strong and hermetic joining technology is required. Autohesion is a self‐bonding method that avoids the need for adhesives. The strengths of autohesive joins using amorphous and semi‐crystalline PEEK films after surface activation using RF plasma were compared. Both types of PEEK films showed successful autohesion after activation with the bond strength of the amorphous sample being twice as high as the bond strength of the semi‐crystalline sample. Plasma treatment increased the autohesion strength of PEEK with no observed change in surface roughness (as measured by profilometer). The water contact angle was reduced by the treatment. X‐ray photoelectron spectroscopy (XPS) was carried out to determine surface chemistry. In the case of the semi‐crystalline surface, plasma treatment increased the relative percentage of C? O functional groups compared to the untreated surface. For treated surfaces nitrogen concentration correlated positively with bond strength while oxygen concentration correlated negatively with the semi‐crystalline PEEK samples and positively with the amorphous PEEK samples. The oxygen groups most likely are formed after the treatment by ambient oxidation are not conducive to bond formation, possibly because of the quenching of radicals that would otherwise form links. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing crystalline lamellae orientation impact on the properties of semi‐crystalline polymer‐clay nanocomposites

Semi‐crystalline polymer‐clay nanocomposite properties are often considered only by their clay dispersion state. The purpose of this work is to highlight texture effects on semi crystalline polymer‐clay properties. Maleic anhydride‐grafted polyethylene nanocomposites with two different processing techniques (Blown Extrusion and Compression) were studied. The processing was shown to induce different crystalline lamellae orientation in the films but with no significant changes in the crystalline lamellae long period, degree of crystallinity, clay particle orientation morphology and dispersion. The impact of these specific textures on the nanocomposites barrier and tensile properties were reported. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1966–1975, 2008     

CaCO3/PEEK复合体系的力学行为和热行为研究

以聚醚醚酮和碳酸钙复合体系为研究对象,考察了偶联剂和填料添加量对复合材料力学行为和热行为的影响.发现磺化聚醚醚酮作为偶联剂能有效地改善材料的力学性能,提高基体树脂的玻璃化转变温度,降低基体树脂的熔点,有助于改善聚醚醚酮的加工条件     

Controlled ring‐opening polymerization of lactones and lactides

1,5‐dioxepan‐2‐one (DXO) is presented as a versatile component in biodegradable polymers for biomedical applications. Copolymerization of DXO and L‐lactide yielded a semi‐crystalline, yet flexible, material where the extent of crystallinity and erosion characteristics were controlled by an appropriate choice of copolymer composition. Crosslinked PDXO was polymerized as a novel biodegradable elastomer. The degradation behavior of these materials were explored in vitro. Microspheres from poly(DXO‐co‐L‐LA) were prepared and shown to be promising candidates for controlled release. The polymer composition and drug solubility provided effective means of controlling the drug delivery pattern.     

Structure evolution of α′‐phase poly(lactic acid)

Poly(lactic acid) films consisting of α′‐forms were prepared and uniaxially drawn. The effects of the draw rate at temperatures above the glass transition temperature on chain conformation, degree of crystallinity, and crystalline phase transformation were investigated by a combination of vibrational spectroscopy (infrared and Raman), differential scanning calorimetry, and wide‐angle X‐ray diffraction (WAXD). It was established that the α′‐crystal's phase of poly(lactic acid) films does not transform into either an α or β crystals on uniaxial drawing at a fixed draw ratio of 4. However, the degree of crystallinity was significantly increased on deformation. The structural change as a function of deformation also promotes an increase in the strain‐induced enthalpic relaxation endothermic peak appearing near the glass transition region. While the overall changes in physical properties can be attributed to the changes in the degree of crystallinity as a function of strain rate, polarized Raman spectra, and WAXD clearly illustrated changes and the differences in the amorphous and crystalline orientation as a function of processing conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1446–1454, 2011     

On the Strain‐Induced Crystalline Phase Changes in Semi‐Crystalline Polymers: Mechanisms and Incidence on the Mechanical Properties

This is a critical survey of the phenomenon of strain‐induced crystalline phase changes in semi‐crystalline polymers. This paper is not concerned with the strain‐induced crystallization of glassy polymers. An examination is made of the experimental data reported in literature, together with a discussion about the mechanism of crystalline phase transitions and about the benefits or prejudices which result on the materials properties. Special attention has been paid to the most largely documented polymers which include materials having either van der Waals, or hydrogen or polar inter‐chain bonding. This concerns polypropylene, polyamide 6, ethylene/vinyl‐alcohol copolymers, poly(vinylidene fluoride) polyesters, and polyethylene. An additional section is devoted to several series of much less documented polymers, from the standpoint of crystal phase changes. Although most of the cases are dealing with films and fibers submitted to tensile drawing, some of the reported studies are concerned with bulk materials. An attempt is made to establish guidelines for the mechanisms of crystalline phase changes based on chain conformation, thermodynamic stability, and plasticity defects.     

The acquirement of desirable dielectric properties of carbon nanofiber composites based on the controlled crystallization

This study focused on uncovering the relationship among nanofiller, crystallization behavior, and dielectric property of polymer composites. The effects of carbon nanofibers (CNFs) and heat treatment on the crystalline structures and dielectric properties of the semi‐crystalline polymers were analyzed by using high density polyethylene (HDPE) as a matrix, which is a representative of non‐polar polymer and contains only one crystal structure. The experimental results showed that the degree of crystallinity, size distribution of crystallity, and relative amount of different crystal planes in the HDPE matrix were changing due to the addition of CNFs. With the increase of CNF loading, the dielectric constant, dielectric loss and AC conductivity of the HDPE composites were increased, presenting a typical percolation characteristic, and the dependence of the dielectric constant on frequency became more obvious. All kinds of electronic transmission, polarization effect, and relaxation behaviors in CNF/HDPE composite system were deeply analyzed. After heat treatment, the degree of crystallinity of HDPE composites was decreased with the enhanced cooling rate. For the CNF/HDPE composites with nanofiller content slightly higher than the percolation threshold, the significant increase of the dielectric constant and the dramatical reduction of the dielectric loss over a wide frequency range were realized simultaneously through rapid cooling treatment. The research indicated that a general commercial polymer material with excellent dielectric properties, which exhibited a high dielectric constant and a low dielectric loss, can be obtained by a simple technical approach different from traditional fabrication method of threshold composites.     

Effects of methylene chloride sorption on the properties of poly(ether ether ketone)

Sorption of methylene chloride by poly(ether ether ketone) (PEEK) has been studied for both amorphous and highly crystalline polymer. After the determination of sorption and desorption curves, the crystallinity of the two materials after desorption was determined both by density and X-ray measurements. The experimental results indicate the existence of solvent-induced crystallization in initially amorphous PEEK and a virtual lack of this process in highly crystalline PEEK. In the latter case, the observed density increase is attributed to solvent compression and a decrease in free volume. The mechanical behavior of both PEEKs is consistent with their crystallinity levels. The mechanical behavior of both PEEKs before and after sorption allows us to discern the separate effects of the two processes to which the presence of methylene chloride in PEEK gives rise, i.e., plasticization and solvent-induced crystallization. © 1994 John Wiley & Sons, Inc.     

Miscibility and properties of polyurethane/benzyl starch semi‐interpenetrating polymer networks

We successfully prepared a series of transparent materials with semi‐interpenetrating polymer networks (semi‐IPNs) from castor‐oil‐based polyurethane (PU) and benzyl starch (BS). The miscibility, morphology, and properties of the semi‐IPN films were investigated with attenuated total reflection/Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy, wide‐angle X‐ray diffraction, electron spin resonance (ESR), ultraviolet–visible spectroscopy, and tensile testing. The results revealed that the semi‐IPN films had good or certain miscibility with BS concentrations of 5–70 wt % because of the strong intermolecular interactions between PU and BS. With an increase in the concentration of BS, the tensile strength and Young's modulus of the semi‐IPN materials increased. The ESR data confirmed that the segment volume of PU in the semi‐IPNs increased with the addition of BS; that is, the chain stiffness increased as a result of strong interactions between PU and BS macromolecules. It was concluded that starch derivatives containing benzyl groups in the side chains more easily penetrated the PU networks to form semi‐IPNs than those containing aliphatic groups, and this led to improved properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 603–615, 2005     

Supramolecular elastomers: Switchable mechanical properties and tuning photohealing with changes in supramolecular interactions

To study light‐triggered self‐healing in supramolecular materials, we synthesized supramolecular thermoplastic elastomers with mechanical properties that were reversibly modulated with temperature. By changing the supramolecular architecture, we created polymers with different temperature responses. Detailed characterization of the hydrogen‐bonding material revealed dramatically different temperature and mechanical stress response due to two different stable states with changes in the hydrogen bonding interactions. A semi‐crystalline state showed no response to oscillatory shear deformations while the melt state behaved as a typical energy dissipative material with a clear crossover between storage and loss moduli. Comparison studies on heat generation after light excitation revealed no differences in photo‐thermal conversion when an Fe(II)‐phenanthroline chromophore was either physically blended into the H‐bonding polymer or covalently attached to the supramolecular network. These materials showed healing of scratches with light‐irradiation, as long as the overlap of material absorbance and laser excitation was sufficient. Differences in the efficiency and rate of photohealing were observed, depending on the type of supramolecular interaction, and these were attributed to the differences in the thermal response of the materials' moduli. Such results provide insight into how materials can be designed with chromophores and supramolecular bonding interactions to tune the light‐healing efficiency of the materials. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1003–1011     

Highly Crystalline and Semiconducting Imine‐Based Two‐Dimensional Polymers Enabled by Interfacial Synthesis

Single‐layer and multi‐layer 2D polyimine films have been achieved through interfacial synthesis methods. However, it remains a great challenge to achieve the maximum degree of crystallinity in the 2D polyimines, which largely limits the long‐range transport properties. Here we employ a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) method for the successful preparation of porphyrin and triazine containing polyimine‐based 2D polymer (PI‐2DP) films with square and hexagonal lattices, respectively. The synthetic PI‐2DP films are featured with polycrystalline multilayers with tunable thickness from 6 to 200 nm and large crystalline domains (100–150 nm in size). Intrigued by high crystallinity and the presence of electroactive porphyrin moieties, the optoelectronic properties of PI‐2DP are investigated by time‐resolved terahertz spectroscopy. Typically, the porphyrin‐based PI‐2DP 1 film exhibits a p‐type semiconductor behavior with a band gap of 1.38 eV and hole mobility as high as 0.01 cm² V^?1 s^?1, superior to the previously reported polyimine based materials.     

Interplay between H‐Bonding and Alkyl‐Chain Ordering in Self‐Assembly of Monodendritic L‐Alanine Derivatives

This paper reports on the synthesis and self‐organizing properties of monodendrons consisting of L ‐alanine at the focal point and alkyl chains with different length at the periphery. The structures of thin films and monolayers are studied by temperature‐resolved grazing‐incidence X‐ray diffraction and scanning force microscopy. The interplay between H‐bonding and ordering of the alkyl chains results in a rich temperature‐dependent phase behavior. The monodendrons form H‐bonded stabilized clusters with the number of molecules depending on the length of the aliphatic chains and temperature. The clusters play the role of constitutive units in the subsequent self‐assembly. Short alkyl chains allow the material to form thermodynamically stable crystalline phases. The molecules with longer side groups exhibit additional transitions from the crystalline phase to thermotropic columnar hexagonal or columnar rectangular liquid‐crystalline phases. In monolayers deposited on highly ordered pyrolytic graphite, the materials show ordering similar to thin films. However, for the compound bearing hexadecyl chains the affinity of the alkyl groups to graphite dominates the self‐assembly and thereby allows epitaxial growth of a 2D lattice with flat‐on oriented molecules.     

Effects of Ar‐ and Ar/O2‐plasma‐treated amorphous and crystalline polymer surfaces revealed by ToF‐SIMS and principal component analysis

The effects of argon (Ar) and a mixture of Ar and oxgyen(Ar/O₂) plasmas on amorphous and semi‐crystalline poly(bisphenol A hexane ether) thin films were investigated by time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS) and principal component analysis (PCA). PCA results of the ToF‐SIMS spectra indicate that an Ar/O₂ plasma produced less physical sputtering and had a higher chemical reactivity than did an Ar plasma, regardless of whether an amorphous or a crystalline surface was involved. However, the chemical differences between the Ar‐ and Ar/O₂‐plasma‐treated semi‐crystalline films were much smaller. The observed results can be explained by the higher resistance of the polymer crystalline regions to physical sputtering and chemical etching. Copyright © 2013 John Wiley & Sons, Ltd.     

Nucleating and clarifying agents for polyolefins

Nucleating agents are used in semi‐crystalline polymer systems (mainly polyolefins) to increase the rate of crystallization. These agents increase degree of crystallinity and lamellae thickness and, hence, improve stiffness and strength. In addition to altered mechanical characteristics, clarifying agents do also improve optical properties. This paper provides a brief overview on nucleating/clarifying agents. The efficiency of such products (e.g. Na‐benzoate, sorbitol acetals) for polypropylene (PP homopolymer, PP copolymer) is evaluated. The clarifiers Irgaclear D ((1,3:2,4)‐dibenzylidene sorbitol) and Irgaclear DM (1,3:2,4‐Bis‐(p‐methylbenzylidene) sorbitol) provide a 3‐dimensional fibrillar structure upon cooling from the polymer melt. This magnified nucleation density yields spherulites with reduced size (< 1micron) ‐ in comparison to non‐nucleated products. Addition of Irgaclear to polypropylene leads to increased clarity, reduced haze and enhanced stiffness of molded parts. Higher recrystallization temperatures results in shorter cycle times and increased throughput during the molding process.     

Hydrogen‐Bonded Liquid Crystalline Materials: Supramolecular Polymeric Assembly and the Induction of Dynamic Function

Liquid crystals are molecular materials that combine anisotropy with dynamic nature. Recently, the use of hydrogen bonding for the design of functional liquid crystalline materials has been shown to be a versatile approach toward the control of simple molecularly assembled structures and the induction of dynamic function. A variety of hydrogen‐bonded liquid crystals has been prepared by molecular self‐assembly processes via hydrogen bond formation. Rod‐like and disk‐like low‐molecular weight complexes and polymers with side‐chain, main‐chain, network, and guest‐host structures have been built by the complexation of complimentary and identical hydrogen‐bonded molecules. These materials consist of closed‐type hydrogen bondings. Another type of hydrogen‐bonded liquid crystals consists of open‐type hydrogen bonding. In this case, the introduction of hydrogen bonding moieties, such as hydroxyl groups, induces microphase segregation leading to liquid crystalline molecular order. Moreover, liquid crystalline physical gels have been prepared by the molecular aggregation of hydrogen‐bonded molecules in non‐hydrogen‐bonded liquid crystals. They show significant electrooptical properties. An anisotropic gel is a new type of anisotropic materials forming heterogeneous structures.     

Cellulose Nanocrystals (CNCs) Induced Crystallization of Polyvinyl Alcohol (PVA) Super Performing Nanocomposite Films

This study is aimed to explore the properties of cellulose nanocrystals (CNC)/polyvinyl alcohol (PVA) composite films with and without 1,2,3,4‐butane tetracarboxylic acid (BTCA), a nontoxic crosslinker. CNC and CNC‐PVA nanocomposite films are prepared using solution‐casting technique. Differential scanning calorimetry (DSC) analyses show that crosslinking increased the glass transition temperature but reduced the melting temperature and crystallinity. Furthermore, high CNC concentrations in the PVA matrix interfere with PVA crystallinity, whereas in specific ratio between CNC and PVA, two different crystalline structures are observed within the PVA matrix. Film surfaces and fracture topographies characterized using scanning electron microscope indicate that at certain CNC‐PVA ratios, micron‐sized needle‐like crystals have formed. These crystalline structures correlate with the remarkable improvement in mechanical properties of the CNC‐PVA nanocomposite films, that is, enhanced tensile strain and toughness to 570% and 202 MJ m^?3, respectively, as compared to pristine PVA. BTCA enhances the tensile strain, ultimate tensile stress, toughness, and modulus of CNC films compared to pristine CNC films. Water absorption of crosslinked CNC and CNC‐PVA nanocomposite films is significantly reduced, while film transparency is significantly improved as a function of PVA and crosslinker content. The presented results indicate that CNC‐PVA nanocomposite films may find applications in packaging, and though materials applications.     

Preparation of HPEEK by Oligomer A2+B3 Approach

A series of hyperbranched poly(ether ether ketones) with different chain length between branching point (L) were prepared using a A₂+B₃ methodology, in which the A₂ is hydroxyl‐terminated PEEK oligomer. The L affects the properties of the polymers such as the inherent viscosity, the degree of crystallinity, the thermal properties of the polymers etc. The polymer with a L₂≈8 had T _g (122.4°C), T _c (200.2°C), and broad T _m (247.4°C). With the increment of L, up to the point L₂≈20 and L₂≈35, the polymers become semi‐crystalline, with a melting point of 300.9°C and 317.9°C, respectively. Their wide angle X‐ray scattering (WAXS) pattern indicated that their crystal structure is exactly the same as that of the linear homopolymer.     

Improving surface quality of polyethylene terephthalate film for large area flexible electronic applications

Lamination is a method utilized to protect flexible electroluminescence device against environmental hazards, such as dust, moisture, and water vapor. The materials are typically joined together using adhesive or cohesion of the materials during the lamination process. Polyethylene terephthalate (PET) is commonly used as the substrate film where electroluminescence patterns are printed. However, PET film has a relatively low surface energy and high contact angle, which would cause relatively weak laminating strength. This paper discusses the use of atmospheric plasma as a surface treatment method to modify PET and laminating films’ interface to improve bonding and laminating quality. Experimental results revealed that atmospheric plasma process reduced the contact angle of both PET and laminating films. Functional groups favoring hydrophilicity were found on the films’ interface after the atmospheric plasma treatment. These effects consequently increased surface energies of both films and favored bonding between the films. The treated films thus had increased laminating strength by approximately six times without compromising the transparency quality.     

Halloysite nanotubes reinforced ultrahigh molecular weight polyethylene nanocomposite films with different filler concentration and modification

Halloysite nanotube/ultrahigh molecular weight polyethylene (HNT/UHMWPE) nanocomposite films were prepared by melt extrusion and thermal extension methods, and the morphology, microstructure, thermal properties, mechanical properties and wettability of these nanocomposite films were investigated with respect to the effects of HNT concentration and modification. HNTs were homogenously distributed and formed self entangled network structures in the UHMWPE matrix. The incorporation of HNT obviously accelerates the crystallization and enhances the thermal stability, mechanical strength and wettability of UHMWPE. However, after HNT concentration exceeds a critical value, the crystallinity and mechanical strength of UHMWPE decrease due to the restriction of HNT obstacles and the existence of large HNT agglomerates. Surface modification of HNT is a good method to further improve the crystallization, thermal stability and mechanical property of UHMWPE nanocomposites, with reduction of nanotube aggregation and strengthening of interfacial bonding between nanotubes and matrix.     

Quantitative nanoscale measurements of the thermomechanical properties of poly-ether-ether-ketone (PEEK)

Understanding the internal structure and organization of semicrystalline polymers, especially at the nanoscale, has many challenges for researchers to date. In this article, we demonstrate a quantitative method for investigating the local viscoelastic properties (i.e., storage and loss moduli, as well as loss tangent) of semicrystalline polyether-ether ketone (PEEK) through the combination of contact resonance atomic force microscopy (CR-AFM) and in situ local heating with a thermal probe. Furthermore, the local viscoelastic properties of the crystalline and amorphous phases were decoupled by performing thermal CR-AFM array mapping near the glass transition temperature of PEEK (T_g, 143 °C). A distinct bimodal distribution of tip-sample interaction was observed for PEEK near its T_g, providing a means to estimate the T_g and the degree of crystallinity of PEEK.