The Solid State Postcondensation of PET, 4

Summary: A new method of polymerising PET in the solid state is proposed in either a gas phase reactor, or in hydrocarbon dispersion. It is shown that the reaction can be carried out efficiently at temperatures on the order of 200–240 °C directly from a prepolymer without the need for a melt phase step. It is shown that the crystal structure of the prepolymer plays a determining role in the kinetics of the SSP reaction.

Schema of the reactor used for gas phase SSP.     

Design of a Microfluidic System to Investigate the Mechanical Properties of Layer‐by‐Layer Fabricated Capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.

Time series of video frames showing capsules being compressed into a constriction.     

Chemical Modification of Terephthalate Polyesters by Reaction with Bis(hydroxyethyl ether) of Bisphenol A

Summary: Copolyesters of terephthalic acid with bis(hydroxyethyl ether) of bisphenol A (BHEEB) in different molar ratios have been synthesized by reactive blending from terephthalate polyesters and by melt polycondensation from the monomers. By this way, bisphenol A groups were inserted in the polyester chains with the aim to obtain polyesters with improved mechanical properties. The insertion of the BHEEB into the polyester backbone is quantitative and does not give rise to side reactions. These copolyesters can be obtained by the chemical recycling of commercial polymers; indeed BHEEB can be synthesized by chemical recycling of bisphenol A polycarbonate and may be incorporated in the polyester by reactive blending with recycled terephthalate polyesters. A new method for BHEEB synthesis by chemical recycling of PC is also presented.

Glass transition temperature (T_g) as function of BHEEB content for copolyesters prepared by reactive blending BHEEB with terephthalate polyesters.     

New Polylactide/Layered Silicate Nanocomposites, 6

The measurement of rheological properties of any polymeric material under molten state is crucial to gain fundamental understanding of the processability of that material. In the case of polymer/layered silicate nanocomposites, the measurements of rheological properties are not only important to understand the knowledge of the processability of these materials, but is also helpful to find out the strength of polymer‐layered silicate interactions and the structure‐property relationship in nanocomposites. This is because rheological behaviors are strongly influenced by their nanoscale structure and interfacial characteristics. In order to get this knowledge in the case of polylactide/montmorillonite nanocomposites, we have studied melt rheological properties of these materials in detail. On the basis of rheological data, we have conducted foam processing of pure polylactide and one representative nanocomposite by a newly developed pressure cell technique using carbon dioxide as a physical‐blowing agent.

The time variation of the elongational viscosity of one of the intercalated polylactide/montmorillonite nanocomposites.     

Artificial Opals as Effect Pigments in Clear‐Coatings

Summary: In this paper, we describe the use of artificial opals from polymer beads as effect pigments in transparent industrial and automotive coatings. For this purpose, we synthesized monodisperse colloids from fluorinated methacrylates by surfactant‐free emulsion polymerization. The fluorinated monomers, in combination with crosslinking, lead to a refractive index contrast, thermal stability, and solvent resistivity necessary for use as effect pigments. After crystallization of the monodisperse polymer beads, crystal flakes with iridescent colors can be obtained. The crystal flakes can act as effect pigments in various transparent industrial and automotive coatings. Due to photonic crystal behavior of effect pigments, color flops up to 100 nm are observed.

Crystal flakes of CS ‐7 as effect pigments in a transparent coating. The diameter of the tube is 5 mm.     

Fracture Behaviour of Styrene/Butadiene Block Copolymers having Different Molecular Architecture

The crack toughness behaviour of styrene/butadiene block copolymers of triblock and star architectures was investigated using instrumented Charpy impact testing. In order to evaluate adequately the toughness behaviour of the investigated materials, different concepts of elastic‐plastic mechanics (J‐integral and crack‐tip opening displacement, CTOD concepts) were used. Although the lamellar block copolymers showed a remarkably enhanced ductility in the tensile test than the neat block copolymer having hexagonal PB cylinders in PS matrix, no pronounced difference in crack toughness was found. This behaviour implies that the tensile strain cannot be regarded as the only parameter defining the toughness value. A brittle/tough transition was observed in a lamellar star block copolymer on blending with a linear thermoplastic elastomeric SBS triblock copolymer.

SEM micrograph showing the details of the stable crack propagation region in a binary block copolymer blend.     

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.     

Effect of Soft Segment Length and Chain Extender Structure on Phase Separation and Morphology in Poly(urethane urea)s

The phase separation and morphology in poly(urethane urea)s were investigated as soft segment length and chain extender structure were varied. Increases in soft segment length led to increased phase separation that resulted in greater mobility of the soft segment. This was shown by lower soft segment glass transition temperatures in differential scanning calorimetry (DSC) as well as a shift of E_max″ and tan δ_max to lower temperatures. Also the structure of the chain extender affected the degree of phase separation and mixing of the soft and the hard blocks in an interphase. Atomic force microscopy (AFM) was used to visualize the structure of the phase‐separated domains. The hard domains were in the form of spheres 5–10 nm, or long needles 5 nm thick and 50–300 nm long. As the soft segment length increased, there were more pure soft segment phase areas between the hard domains. At high hard segment content, a larger scale structure was found, consisting of both hard and soft segments.

DSC thermograms of poly(urethane urea)s containing different soft segment lengths.     

Novel Phenol‐Formaldehyde Resins, 2. Resols Prepared Using Reactive Solvents

New results on the method of preparation of phenol‐formaldehyde resins from phenol and multihydroxymethyl derivatives of some ketones are presented. The latter, known as the reactive solvents of melamine, were prepared by reacting acetone and methyl ethyl ketone with excess of formaldehyde. A novel group of resins of resol type has been obtained. The structure of products is discussed and compared to that of classical resols. The fragments of ketones have been found incorporated into the structure of resins.

Temperature dependence of viscosity of a classical resol and of the resols modified with reactive solvents.     

Dynamic Mechanical and Thermal Properties of Phenylethynyl‐Terminated Polyimide Composites Reinforced With Expanded Graphite Nanoplatelets

Summary: This article reports on the dynamic mechanical and thermal properties of thermosetting phenylethynyl‐terminated polyimide (PETI‐5) composites reinforced with expanded graphite (EG) nanoplatelets having various average particle sizes and content. The EG nanoplatelets with varying particle sizes were prepared by different pulverization techniques through intercalation and exfoliation of natural graphite flakes. The effect of the EG particle size and concentration of the thermal behavior of PETI‐5/EG composites was investigated with several thermal analysis methods (DMA, TMA, and DSC). The storage modulus dynamic mechanical properties and glass transition temperature significantly increased with increasing concentration of EG nanoreinforcements regardless of size. The coefficient of thermal expansion significantly decreased, especially in the glass transition region.

     

The Solid State Postcondensation of PET, 1

Summary: A review of the processes underlying the solid state postcondensation of poly(ethylene terephthalate) (PET) is presented. Fundamental aspects of the reactions are treated, and it is shown that the rate of polycondensation in the solid state depends on the relative rates of two types of diffusion. On the one hand, the diffusion of reaction by‐products (physical diffusion) controls the rate of the forward reactions. And on the other hand the diffusion of end‐groups (chemical diffusion) allows the reaction to proceed.

The transesterification of BHET to form PET.     

Theoretical Model for the One‐Dimensional Temperature and Stress Calculation of Simple Hot Plate Welded Geometries

In the field of hot plate welding, experimental investigations show that the stress cracks are caused by inherent stresses in the component, which are induced in the part while it is being heated on the tool. For the better understanding of the process parameters and their effects on the phenomenon of stress cracking, a simple theoretical model for the calculation of the temperature and the stress field is to be developed. The application of the presented method shows the effects of the process parameters on the phenomenon of stress cracking and correlates with the experimental results of further investigations.

Theoretical stress distribution.     

Formation of in situ CB/PET Microfibers in CB/PET/PE Composites by Slit Die Extrusion and Hot Stretching

Summary: In this present study, the in situ fabrication of a microfibrillar composite based on poly(ethylene terephthalate) (PET), polyethylene (PE), and carbon black (CB) is attempted. PET and CB were first melt mixed. The CB/PET compound and PE were subsequently melt extruded through a slit die and then hot stretched. The morphological observation of the as‐stretched extrudate indicated that well‐defined microfibers of CB/PET compound could be generated at appropriate CB contents and a fixed hot stretch ratio. In addition, CB was always selectively located in PET. The microfibrillar CB/PET/PE composite has the potential to be a new electrically conductive polymer composite.

Morphology of the carbon black/poly(ethylene terephthalate)/polyethylene (PE) composite after additional mixing in the mixer at the processing temperature of PE.     

Influence of Screw Speed on Electrical and Rheological Percolation of Melt‐Mixed High‐Impact Polystyrene/MWCNT Nanocomposites

The influence of screw speed on the electrical and rheological percolation of HIPS/MWCNT composites prepared via melt mixing was investigated. Microscopic examination of these composites using POM, FESEM and HRTEM revealed optimum MWCNT dispersion was achieved at intermediate screw speeds. On addition of MWCNTs to HIPS, the electrical conductivity of HIPS increased by up to 12 orders of magnitude. At screw speeds up to 100 rpm an electrical percolation of 1–3 wt.‐% was achieved. This increased to 3–5 wt.‐% when the screw speed was increased to 150 rpm. The onset of a rheological percolation was detected for an MWCNT loading of 5 wt.‐%, irrespective of screw speed employed. An up‐shift in the Raman G‐band of 24 cm^?1 was observed, implying strong interfacial interaction between HIPS and MWCNTs.

     

Preparation and Characterization of Conducting Systems based on EPDM/PE/PS‐co‐DVB/HSb

Summary: Blends of different compositions were prepared from: a thermoplastic elastomer (EPDM), a low density polyethylene (PE), a polystyrene crosslinked with a small amount of divinylbenzene (PS‐co‐DVB) and an inorganic proton conductor: antimonic acid (HSb). The blends obtained were sulfonated heterogeneously with chlorosulfonic acid and were then structurally and electrically characterized by means of the following techniques: differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), crystallization kinetics under non‐isothermal conditions and complex impedance spectroscopy.

Dynamic mechanical analysis for EPDM and EP‐3 blends series.     

Control of Biodegradability of Polylactide via Nanocomposite Technology

Polymer/layered silicate nanocomposite technology is not only suitable for the significant improvement of mechanical and various other materials properties of virgin polymers, it is also suitable to enhance the rate of biodegradation of biodegradable polymers such as polylactide. The biodegradability of polylactide in nanocomposites completely depends upon both the nature of pristine layered silicates and surfactants used for the modification of layered silicate, and we can control the biodegradability of polylactide via judicious choice of organically modified layered silicate.

Biodegradation of neat PLA and various PLA/OMLS nanocomposites recovered from compost with time.     

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.     

Correlating Polymer Parameters to the Entire Molecular Weight Distribution: Application to the Melt Index

Summary: A method that takes into account the entire molecular weight distribution (MWD) for the prediction of polymer point properties and/or indexes is presented. The method is based on the convolution of the polymer mass molecular weight distribution and an empirical kernel function. Thus, the problem of relating the polymers properties to the MWD is reduced to the estimation of this empirical function. The proposed methodology is able to successfully predict melt indexes (MI) of a set of poly(propylene) samples.