Improvement of Chromatic Aberration of the Plastic Rod‐Lens Array, 2

Summary: We propose in this paper a new plastic rod‐lens with low chromatic aberration. Since a plastic rod‐lens has a parabolic refractive index distribution, it usually also shows a distribution of Abbe number. This Abbe number distribution is thought to cause the chromatic aberration of the plastic rod‐lens array. We have studied novel materials for a new plastic rod‐lens with low chromatic aberration and have provided new transparent polymer blends consisting of two polymers with different refractive indices and with almost equal Abbe numbers by using a fabrication process based on photopolymerization of methacrylate monomer(s) in the presence of other methacrylic polymers. The process can give new transparent polymer blends which cannot be formed using conventional techniques for polymer blend formation. In this work, tricyclo[5,2,1,0^2,6]deca‐8‐yl methacrylate is used as a high refractive index monomer and tert‐butyl methacrylate is used as a low refractive index one. By using polymer blends including these monomer units, we have created a plastic rod‐lens with lower chromatic aberration.

Molecular structures of comonomers in the study.     

Safety in Emulsion Polymerization Reactors: An Experimental Study

Summary: The risk parameters of the high‐solids‐content emulsion copolymerization of vinyl acetate/butyl acrylate/acrylic acid (78.5/18.5/3 wt.‐%) were studied. The effect of the polymer/monomer ratio, the total solids content, the initiator/monomer ratio, the non‐swollen polymer particle size, and the process temperature on the onset temperature for runaway, the adiabatic temperature increase, and the maximum temperature and pressure achieved was studied. These data are needed to determine the safety limits for the variables of this system considering the worst case scenario; namely, a runaway reaction under adiabatic conditions. It was found that the onset temperature is always below the typical process temperature for this system (70–80 °C). Therefore, in the case of a cooling system failure (i.e., electrical failure) the runaway reaction will take place. Relatively high pressures (up to 6 bar) were monitored during the runaway.

Evolution of the maximum pressures reached during all the experiments versus the polymer‐to‐monomer ratio ‘r’ and the process temperature ‘T_work’.     

Self‐Assembling of SBS Block Copolymers as Templates for Conductive Silver Nanocomposites

Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.

     

The Influence of the Irradiation Temperature on the Ratio of Chain Scission to Branching Reactions in Electron Beam Irradiated Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) films have been irradiated by electron beam in vacuum at various temperatures ranging from room temperature up to temperatures far above the melting temperature. Changes of the chemical structure have been analyzed by ¹⁹F solid‐state NMR and IR spectroscopy. The concentration of several structures generated by irradiation increases with increasing irradiation temperature up to the beginning of the thermal degradation. The molar ratio of >CF? branching points to ? CF₃ end groups changes with crossing of the melting temperature. The generation of >CF? branching points is accelerated if the PTFE is irradiated in the molten state, where branching reactions become more important.

     

On Toughness and Stiffness of Poly(butylene terephthalate) with Epoxide‐Containing Elastomer by Reactive Extrusion

Summary: To obtain a balance between toughness (as measured by notched impact strength) and elastic stiffness of poly(butylene terephthalate) (PBT), a small amount of tetra‐functional epoxy monomer was incorporated into PBT/[ethylene/methyl acrylate/glycidyl methacrylate terpolymer (E‐MA‐GMA)] blends during the reactive extrusion process. The effectiveness of toughening by E‐MA‐GMA and the effect of the epoxy monomer were investigated. It was found that E‐MA‐GMA was finely dispersed in PBT matrix, whose toughness was significantly enhanced, but the stiffness decreased linearly, with increasing E‐MA‐GMA content. Addition of 0.2 phr epoxy monomer was noted to further improve the dispersion of E‐MA‐GMA particles by increasing the viscosity of the PBT matrix. While use of epoxy monomer had little influence on the notched impact strength of the blends, there was a distinct increase in the elastic stiffness. SEM micrographs of impact‐fracture surfaces indicated that extensive matrix shear yielding was the main impact energy dissipation mechanism in both types of blends, with or without epoxy monomer, and containing 20 wt.‐% or more elastomer.

SEM micrographs of freeze‐fractured surfaces of PBT/E‐MA‐GMA blend illustrating the finer dispersion of E‐MA‐GMA in the presence of epoxy monomer.     

Effect of Compatibilizer Concentration on Rheological Behavior,Morphologies, and Mechanical Properties of PVDF/TPU Blends

The rheological behavior, morphologies, and tensile properties of reactively compatibilized PVDF/TPU blends are reported. Using PVDF‐g‐AAc as the compatibilizer, PVDF/TPU 90/10 and 10/90 blends are prepared. The carboxylic acid groups of PVDF‐g‐AAc react with the urethane linkages of TPU during melt blending to generate in situ PVDF‐g‐AAc‐g‐TPU which leads to compatibilization of PVDF/TPU blends. The introduction of PVDF‐g‐AAc into the PVDF/TPU blends causes an increase in viscosity. The rheological behavior of the compatibilized PVDF/TPU 90/10 and 10/90 blends are well described by the generalized Zener model. The addition of the compatibilizer PVDF‐g‐AAc reduces the dispersed‐phase domain size and narrows the size distribution. ?Author: The summary has been shortened to comply with the maximum of 700 characters. Pls check/confirm changes!?

     

Temperature Sensitive Behavior of Poly(N‐isopropylacrylamide) Grafted Onto Electron Beam‐Irradiated Poly(propylene)

Summary: N‐Isopropylacrylamide (NIPAAm) was graft‐polymerized from its acetone solution onto poly(propylene) (PP) films, after electron‐beam irradiation in the presence of air oxygen. The effects of pre‐irradiation dose as well as monomer concentration, reaction temperature and reaction time on the grafting efficiency were investigated. Typical conditions for achieving maximum grafting yield were observed for 1 M monomer concentration, after PP pre‐irradiation with a 300 kGy dose and a reaction temperature of 50 °C. The location of the graft polymerization was examined by different methods including measurements of dimensional variations, calorimetry, SEM and AFM. The temperature‐responsive behavior of grafted copolymer was studied by swelling and contact angle measurements at different temperatures.

Temperature dependence of the swelling ratio in water as a function of temperature.     

Poly(vinyl alcohol)/Clay‐Based Nanocomposite Hydrogels: Swelling Behavior and Characterization

Polymer/clay composite hydrogels were prepared based on PVA hydrogels containing 3–10 wt.‐% MOM. Their microstructure and morphology were studied by FT‐IR, WAXS and SEM, whereas the interactions between MOM and PVA were evaluated by thermal analyses. The swelling ratios for the PVA/MOM hydrogels decrease with increasing MOM content. WAXS results indicate that MOM was intercalates, and DSC results show a strong interaction between PVA and MOM. This interaction results in a stable network, which is confirmed by the elastic modulus and the thermal decomposition behavior of the hydrogels. Therefore, MOM acts as a co‐crosslinker, improving the stability of the network.

     

The Reinforcement of Elastomeric Networks by Fillers

Summary: The mechanisms involved in rubber reinforcement are discussed. A better molecular understanding of these mechanisms can be obtained by combining characterization of the mechanical behavior with an analysis of the chain segmental orientation accompanying deformation. While the strain dependence of the stress is the most common quantity used to assess the effect of filler addition, experimental determination of segmental orientation can be used to quantify the interfacial interactions between the elastomeric matrix and the mineral inclusions.

SEM micrograph of natural rubber containing 10 wt.‐% of organomodified clay.     

Use of Acrylic Functionalized (Meth)acrylic Cross‐Linked Polymer Microparticles in Photopolymerized Acrylic Films

The effect of reactive (meth)acrylic cross‐linked polymer microparticles (reactive CPM, also called reactive microgels) used as cross‐linking agents has been studied on the thermo‐mechanical properties of different photopolymerized thin films. The matrix was based on the copolymerization of isobornyl acrylate and ethoxy ethoxy ethyl acrylate or butyl acrylate. Various concentrations of CPM were initially blended with the monomers. These solutions were photopolymerized under UV radiation to obtain hard and transparent films. Since CPM were reactive respect to monomers, they acted as multifunctional cross‐linkers, resulting in networks after polymerization. The well distributed and highly functional CPM which connected acrylate linear chains worked as well defined chemical clusters and gave to the networks a very unique structure. By varying the reactive CPM concentration, the relationship between the number of double bonds introduced into the network by the CPM acting like cross‐linkers and the rubbery modulus of the films was determined from viscoelastic measurements. The structure of CPM, the average functionality and also crystallinity were modified to change networks properties. In addition, reactive groups have been preferentially introduced at the surface vicinity by using a new functional stabilizing agent. CPM were also compared to linear polymers with the same composition. From viscoelastic properties, it is concluded that CPM are very efficient cross‐linkers. However, very high CPM incorporation led to high extent of intramolecular reaction, reducing the cross‐linking efficiency. During thermal aging, CPM and linear copolymer seemed to rearrange leading the film structure to an equilibrium state.

TEM micrograph of a photopolymerized film (30 wt.‐% of CPM‐0% ODA + 70 wt.‐% of IBOA/EEEA) after thermal aging.     

Polymerization Kinetics and Characterization of Dual Cured Polyurethane‐Acrylate Nanocomposites for Laminates

Summary: Four different types of montmorillonites have been dispersed by sonication at 50 °C into a propoxylated aromatic epoxy diacrylate oligomer to achieve interlayered or exfoliated nanocomposites. A thermally‐induced crosslinking reaction, forming a polyurethane network in the presence of 7 wt.‐% of a montmorillonite, has been promoted by addition of an allophanate modified polyisocyanurate based on hexamethylene diisocyanate. The kinetic behavior of the network formation has been studied at 25, 40 and 60 °C by following the disappearance of the isocyanate vibrational band found at 2 270 cm^?1. A tight crosslinked polyurethane acrylate network has been achieved by a subsequent dual UV curing promoted by a photoinitiator mixture (0.6 wt.‐%) added to the reactive mixture because of further reactions occur to the acrylate double bonds. The photopolymerization kinetic has been investigated on the different thermally treated polyurethane nanocomposite networks by Real Time FTIR spectroscopy monitoring the changes of the IR band at 810 cm^?1 assigned to the acrylate double bond vibrations. The influence of the different montmorillonite clays on the final nanocomposite morphology has been investigated by using XRD and SEM. Finally, the use of these mixtures as internal layer between two modified surface PET films has been also studied for the laminate production. The based‐PET laminate films have been characterized by determining the bending resistance and optical properties as a function of different nanofillers.

Bending resistance of the dual cured nanocomposite laminates containing 7 wt.‐% as a function of nanofiller types.     

Thermo‐Physical and Impact Properties of Epoxy Containing Epoxidized Linseed Oil, 2

Summary: Biobased neat epoxy materials containing epoxidized linseed oil (ELO) were processed with an amine curing agent. A defined amount of diglycidyl ether of bisphenol F (DGEBF) was replaced by ELO. The thermophysical properties of the amine‐cured biobased neat epoxy were measured by dynamic mechanical analysis (DMA). The Izod impact strength increased with an increase in the amount of ELO added. The change in the Izod impact strength was correlated with the thermophysical properties measured by DMA.

Relation between the Izod impact strength and loss factor for amine‐ and anhydride‐cured ELO‐containing epoxy resins.     

In Situ Polymerisation of Polyamide‐6 Nanocompounds from Caprolactam and Layered Silicates

An in situ process for the production of polyamide‐6 nanocompounds is investigated as an alternative to melt compounding. During the in situ production, the layered silicates are dispersed in the monomer caprolactam before the polymerisation in a twin screw extruder, leading to an intercalation of the silicates. The production of a polyamide compound containing 0, 2 and 4 wt.‐% nanoscale silicates was successful. An improvement of the elastic modulus of approximately 30–60% was reached. The figure shows the TEM micrograph of a nanocompound containing 2 wt.‐% nanoclay at a magnification of 30 000×.

     

Enhanced Exfoliation of Organoclay in Partially End‐Functionalized Non‐Polar Polymer

We found that enhanced exfoliation of clay up to 20 wt.‐% in non‐polar polybutadiene (PB) if the PB was blended with a relatively small fraction of hydroxyl‐terminated PB (HTPB). The choice of an intermediate polymer composition to enhance exfoliation was motivated by theoretical predictions of end‐functionalizing effects of Balazs, Farmer, and coworkers. A combination of X‐ray diffraction and rheological measurements were used to optimize HTPB content for enhanced exfoliation. We also observed the competition of the kinetic and thermodynamic processes during the ripening of the exfoliated clay structure.

     

A Novel Route to Multiphase Polymer Systems Containing Nano‐Droplets: Radical Polymerization of Vinylic Monomers in Gelled Water‐in‐Oil Miniemulsions

Summary: A new strategy for the synthesis of composite polymers with larger volume fraction of aqueous inclusions less than 1 µm in diameter is presented. A water‐in‐oil miniemulsion of aqueous droplets in a continuous, cross‐linkable monomer phase is prepared. The addition of an organo‐gelator allows the immobilization of the droplets in a solid gel, thus avoiding the usual demixing upon polymerization of the continuous phase. This pregelled system is then converted into a composite polymer by photoinitiated free radical polymerization. Such coatings may be used for an improved climate control of buildings or as a deposit for the controlled release of actives from polar nano‐droplets.

SEM image of a cross‐linked composite polymer showing controlled droplet inclusions with a maximal diameter of 500 nm.     

Ultrafine Electrospun Polyamide‐6 Fibers: Effects of Solvent System and Emitting Electrode Polarity on Morphology and Average Fiber Diameter

Summary: In the present contribution, polyamide‐6 (PA‐6) solutions were prepared in various pure and mixed‐solvent systems and later electrospun with the polarity of the emitting electrode being either positive or negative. The PA‐6 concentration in the as‐prepared solutions was fixed at 32% w/v. Some of the solution properties, i.e., shear viscosity, surface tension, and conductivity, were measured. Irrespective of the polarity of the emitting electrode, only the electrospinning of PA‐6 solution in formic acid (85 wt.‐% aqueous solution) produced uniform electrospun fibers, while solutions of PA‐6 in m‐cresol or sulfuric acid (either 20 or 40 wt.‐% aqueous solution) did not. In the mixed‐solvent systems, formic acid (85 wt.‐% aqueous solution) was blended with m‐cresol, sulfuric acid (either 20 or 40 wt.‐% aqueous solution), acetic acid, or ethanol in the compositional range of 10–40 vol.‐% (based on the amount of the minor solvent). Generally, the average fiber diameter increased with increasing amount of the minor solvent or liquid. Interestingly, the diameters of the fibers obtained under the negative electrode polarity were larger than those obtained under the positive one.

Optical images of electrospun fibers from solutions of polyamide‐6 in a mixed solvent of 85 wt.‐% formic acid and 20 vol.‐% m‐cresol under positive (left) and negative (right) electrode polarity.     

An Investigation of Friction and Wear Behaviors of Polyimide/Attapulgite Hybrid Materials

Summary: PI/AT hybrid materials were prepared by blending of poly(amic acid) and purified AT as a type of fibrillar clays. The friction and wear behaviors of the PI hybrids were evaluated on a ball‐on‐disc wear tester. The particle size of AT in the hybrid containing 5 wt.‐% AT was about 10–100 nm in diameter and 100–1 000 nm in length. Tensile tests on the PI hybrids showed that the strength and the toughness of PI/AT hybrid materials were improved simultaneously when the content of AT was less than 5 wt.‐%. The friction coefficient and wear rate of the PI hybrids first decreased and then increased with increasing content of AT. The wear rate of the hybrid containing 3 wt.‐% AT was more than 6 times lower than that of pure PI. SEM examination of worn surfaces showed that type of wear changed from adhesive wear of pure PI into abrasive wear of the PI hybrids with adding AT to PI matrix. Debris analysis suggested that AT as filler inside the PI matrix could prevent the formation of bigger debris and a chemical reaction that occurred during the friction process of pure PI but not in the hybrids.

A plot of the calculated wear rate versus filler content.     

Influence of Catalyst Content on the Thermal and Mechanical Properties of Epoxy Resins Initiated by a Cationic Latent Thermal Catalyst at Elevated Temperatures

The effect of catalyst content on the thermal and mechanical properties of diglycidyl ethers of bisphenol A (DGEBA)/BPH system was investigated at elevated temperatures. The contents of the catalyst, N‐benzylpyrazinium hexafluoroantimonate (BPH), examined were 0.5, 1, and 3 wt.‐% and the elapsed heating time was varied from 0 to 1 024 h. As a result, the thermal‐oxidative resistance and mechanical properties, including flexural strength, elastic modulus in flexure, and impact strength showed a maximum value at 1 wt.‐% BPH. By increasing the elapsed time to 4 h, the thermal and mechanical properties of the specimens were also improved. These results showed that the internal structure of the epoxy system was stabilized and post‐cured as the elapsed time increased, resulting in an improvement of the thermal and mechanical properties of the specimens.

Impact strength of the DGEBA/BPH system as a function of BPH content and elapsed heating time.     

Laccases to Improve the Whiteness in a Conventional Bleaching of Cotton

This study reports for the first time on the enhancement of the bleaching effect achieved on cotton using laccase enzyme. Laccases applied in short‐time batchwise or pad‐dry processes prior to conventional peroxide bleaching, improved the end fabric whiteness. The whiteness level reached in the combined enzymatic/peroxide process was comparable to the whiteness in two consecutive peroxide bleaches.

Effect of 10 min laccase pre‐treatment at 60 °C, pH 5 on fabrics whiteness before and after a conventional hydrogen peroxide bleaching.