Improved Design of Shearing Sections with New Calculation Models Based on 3D Finite‐Element Simulations

New models for the Maddock and spiral shearing sections have been developed, employing three‐dimensional finite element analysis (3D FEA). These models describe the pressure‐throughput and power consumption behavior of the shearing sections for both the extrusion and the injection molding process and have been implemented in the REX 6.0 and PSI 4.0 simulation software. As a consequence it is now possible to describe the process behavior of these shearing sections within just a few seconds with the accuracy of FEA calculations.

Actual Maddock shearing section (left) and actual spiral shearing section (right).     

Development of a 3D‐Finite Element Module for the Prediction of the Fibre Orientation in Injection Moulded Parts

This article presents a 3D‐finite element simulation package for the prediction of the fibre orientation in injection moulding. The fibre orientation is calculated by using a mathematical model based on orientation tensors, which not only takes into account the 3D‐flow field, but also the shape of the fibres and the fibre‐fibre interaction. The tensor model has been verified in many scientific investigations and has proven to yield satisfying results. Therefore we decided to use this model for implementation into a 3D‐finite element simulation package, which is currently being developed at the Institute of Plastics Processing (IKV) at RWTH Aachen University, Germany. The implementation of this model using both the finite element method and the finite volume method is described and the different parameters used in this model are analysed and discussed separately, as are the parameters used for the injection moulding process. The results obtained are compared to similar results from literature.

Model of the flow channel (10 mm × 10 mm × 100 mm) used for the simulations.     

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.     

Long‐Aliphatic‐Segment Polyamides: Salt Preparation and Subsequent Anhydrous Polymerization

Long‐aliphatic‐segment polyamides were prepared based on hexamethylenediamine and α,ω‐(CH₂)_x biosynthetic diacids (x = 10, 11, 12). The pertinent monomers (salts) were isolated as solids, thoroughly characterized for the first time, and then submitted to an anhydrous melt prepolymerization technique. The obtained prepolymers exhibited in the range of 5 100–11 800 g · mol^?1, and the molecular weight was further increased by up to 55% through solid‐state finishing. The suggested overall polyamidation cycle was conducted at short melt‐reaction times, so as to avoid any thermal degradation, and was proved efficient, indicating similar reactants polymerizability independently of the methylene content.

     

Structure Studies on 6a-Thiathiophthenes and Related Compounds

The results from structure studies on 6a-thiathiophthenes show that different substituent groups perturb the bonding in the three-sulphur sequence to different degrees. Both equal and unequal S? S bonds occur in symmetrically as well as in unsymmetrically substituted derivatives. The specific effect of methyl and phenyl substituents on the sulphur-sulphur bonding may be described by the results from CNDO/2 calculations on mono-methyl and mono-phenyl substituted 6a-thiathiophthenes. Molecular packing and intermolecular close contacts also seem to affect the S? S bonding. The structures of equally substituted 6a-thiathiophthene analogues with and show, when compared with the equivalent 6a-thiathiophthene, that and cause a pronounced change in the S? S bonding, while the perturbation caused by is negligible. In symmetrical 6a-thiathiophthene analogues with and , the average bond length in the linear three-atom sequence is 9 – 12% longer than the respective single bond.     

Studies of Injection‐Moulded Isotactic Poly(propylene) by Synchrotron WAXD/SAXS: Effects of Nucleating Agent on Morphological Distribution

The morphological distribution of injection‐moulded isotactic poly(propylene) (iPP) plates in the presence of nucleating agents was extensively investigated using synchrotron radiation. The commercial PP compound was injection‐moulded under a variety of different conditions in order to explore the effects of shear flow and temperature on the morphology and morphological distribution. The iPP structures obtained were characterized using the degree of crystallinity, α‐phase orientation index, β‐phase index, long spacing of lamellae, and the thickness of both crystalline and amorphous lamellae. These parameters were plotted as a function of position through the plate depth for the injection‐moulding conditions. Unlike relatively pure iPP, the distributions of crystallinity and α‐phase orientation index in this commercial iPP are independent of position through the plate depth. The “skin‐core” structure that is generally found for injection‐moulded iPP is not present because of the addition of nucleating agents. The β‐phase of iPP has the same distribution through the plate depth as that expected for iPP without nucleating agents. Additionally, the lamellar dimension is found to be independent of position through the plate depth and the fraction of noncrystalline materials residing outside the lamellar stacks can be up to about 30%. The results indicate that the properties of different injection‐moulded iPP grades should be investigated individually.

Typical WAXS patterns of the sample S9 at different labeled distances from the surface. The patterns are vertically shifted for clarity.     

The Effect of Particle Matrix Adhesion on the Mechanical Properties of Silica Filled Cyanate Ester Composites

Summary: The effect of silica and its surface treatment on the mechanical properties of composites was studied as part of the evaluation of cyanate ester matrices as potential electronic encapsulants. Three filler surface treatments were used, as a qualitative interfacial adhesion scale, in an attempt to gauge the magnitude of interfacial adhesion between untreated filler and the cyanate ester matrix. There was strong interfacial adhesion between matrix and untreated filler. The level of silica content most affected composite modulus and fracture toughness. Filler surface treatment most affected composite strength and fracture toughness/energy. Composite fracture was found to occur via crack pinning and/or crack blunting depending on the strength of adhesion. The composites evaluated were found to possess suitable mechanical properties for potential use as electronic encapsulants.

     

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.     

An Approach to Calculating Wear on Annular Non‐Return Valves

The serviceability of non‐return valves has a major influence on the productivity of the injection molding process. During a meeting of experts held at our Institute, it was seen that closing behavior and wear are the key problems encountered in practice. The conducted investigations to tackle these questions have shown that both an improved closing behavior and a lower level of wear can be achieved by reducing the inside radius of the locking ring.

Pressure profile over the length of a non‐return valve (n = 0.4; = 25 000 mm³/s).     

Global Concept for Describing and Investigation of Wall Slip Effects in the Extrusion Process

When it comes to the design of extrusion line components such as single‐screw extruders or extrusion dies, no one has yet succeeded in developing a well‐functioning concept for wall‐slipping materials. This article examines the fundamental influences of the wall slippage effect on flow behavior in the extrusion die and plastification unit. New and extended methods of calculation for describing this flow phenomenon are presented for both these extrusion line components, and the general possibilities for linking the two approaches are discussed.

Diagram of the flow curve (τ = shear stress, = shear rate) of wall‐slipping plastics for constant pressure.     

The Solid State Postcondensation of PET, 3

Summary: It was demonstrated that it is possible to produce prepolymers with a number‐average degree of polymerisation on the order of 5–40 directly in a liquid‐liquid dispersion in less than three hours. It was also shown that prepolymers made via this route and rapidly crystallised by the addition of a dispersant at ambient temperature are more porous than prepolymers made in an industrial liquid melt process.

SEM micrograph of prepolymers pLL‐PTA with \overline {DP} _{\rm n} = 28, d_p ∈ 63–125 μm.     

Preparation and Characterization of Polycarbonate/Poly(propylene)/Attapulgite Ternary Nanocomposites with the Morphology of Encapsulation

Summary: Ternary nanocomposites based on polycarbonate (PC), poly(propylene) (PP), and attapulgite (AT) were prepared via the method of two‐step melt blending, by which the AT was blended with PP prior to compound with PC. Structure and properties of the ternary PC/PP/AT nanocomposites were investigated. The degradation of PC triggered by AT during direct blending process can be inhibited effectively by using two‐step melt blending. It was found that the morphology of encapsulation structure like sandbag was formed in PC matrix, where PP encapsulated AT fibrillar single crystals. DSC experiments showed that in PC/PP/AT ternary nanocomposites, AT had a strong heterophase nucleation effect on PP, resulting in the enhancement of crystallization degree and the crystallization temperature of PP. DMA and mechanical property results showed that the ternary nanocomposites exhibited good balanced toughness and stiffness.

TEM photograph of PC/PP/AT ternary nanocomposite.     

A Fully Polymeric Mouldable Microfluidic Device. Part 1: The Process of Design

Microfluidic devices as used, e.g., in lab‐on‐a‐chip and micro‐total‐analysis systems, are frequently fabricated using silicon or polydimethylsiloxane (PDMS)‐based technologies, both with their known disadvantages. Here, we design a fully polymeric, multifunctional microfluidic reactor device, using an alternative fabrication method, the two‐component co‐injection moulding technology, in which different polymer combinations—generally a flexible and a rigid thermoplastic polymer—can be applied. The prototype device is based on an ambi‐symmetrical design, combining two identical shells, that are each folded to occupy a 160 × 90 mm² space and subsequently stacked into a 4 (double) layer system. One microfluidic reactor unit includes six different in‐ and output connections, six peristaltic pumps (built up from three membranes each), eighteen volume‐neutral, recoverable control valves, two fluid storages, and two efficient, flow splitting, rotating and recombining, serpentine mixers. The mixers realize an almost perfect baker's transformation and possess ten elements that create 2 × 4¹⁰ layers with an individual striation thickness of 0.5 nm in 10 s. The total reactor volume amounts 7 mL. The capacity of the peristaltic pumps, with their stroke of 0.5 mm, equals about 35 µL · s^?1 at an actuation frequency of 5 Hz. Actuation occurs by air pressure. One microfluidic device can be endlessly connected to its replicas.

     

Construction of 2,3,4,7‐Tetrahydro‐1,2,4,5‐oxatriazepines via [4+3] Cycloadditions of α‐Halogeno Hydrazones with Nitrones

In the presence of sodium carbonate, the [4+3] cycloadditions of α‐halogeno hydrazones with nitrones were performed efficiently, and affording 2,3,4,7‐tetrahydro‐1,2,4,5‐oxatriazepines in moderate to high yields.

     

Strongly Photosensitive and Fluorescent F8T2 Electrospun Fibers

Electrospun fibers of poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐bithiophene] (F8T2) with exceptional electro‐optical performance are obtained. The I/T characteristics measured in fibers with 7–15 µm diameter and 1 mm length show a semiconductor behavior; their thermal activation energy is 0.5 eV and the dark conductivity at RT is 5 × 10^?9 (Ω cm)^?1. Besides exhibiting a photosensitivity of about 60 under white light illumination with a light power intensity of 25 mW · cm^?2, the fibers also attain RT photoluminescence in the cyan, yellow, and red wavelength range under ultraviolet, blue, and green light excitation, respectively. Optical microscope images of F8T2 reveal homogeneous electrospun fibers, which are in good agreement with the uniformly radial fluorescence observed.

     

Micromechanical Processes in PET/PC Multilayered Tapes: High Voltage Electron Microscopy Investigations

Summary: A totally new kind of multilayered tape consisting of two macroscopically ductile polymers (PET and PC) was studied using high voltage electron microscopy (HVEM). Both components were co‐extruded as uniform laminates with thousands of alternating layers. The multilayered PET/PC samples were annealed at high temperature. Investigation of the multilayered PET/PC tapes with various compositions clearly demonstrated a transition of the microdeformation mechanism which was dependent on the thickness of the individual layers. The annealing of the tapes led to a significant change in the deformation behavior. However, no lamellae formation was revealed in the PET phase after annealing, leading to the assumption of constrained crystallization in very thin PET layers.

     

A Novel Impact Modifier for Nylon 6

A new carboxylated styrene‐butadiene rubber (CSBR) in ultrafine powder form was used to modify the properties of nylon 6. The nylon 6/CSBR blends possessed higher toughness than nylon 6/maleic anhydride‐grafted polyethylene‐octene elastomer (POE‐g‐MAH) system. TEM micrographs revealed the fine dispersion of CSBR particles with a diameter of 150 nm. The effective toughening of nylon 6 with CSBR was attributed to the good interface, fine dispersion, and shear yielding.

TEM photograph of undeformed Nylon 6/CSBR (80/20) blend (×40 000).     

Morphology Dependent Double Yielding in Injection Molded Polycarbonate/Polyethylene Blend

Summary: Polycarbonate (PC)/polyethylene (PE) blend was injection molded at different molding temperatures. The morphological observation by scanning electronic microscope (SEM) indicated that the sample molded at 190 °C contained only uniformly dispersed spherical PC particles. The samples molded at 230 and 275 °C had a typical skin‐core structure, and there were many injection‐induced PC fibers in the subskin. While the sample molded at 190 °C had the usual stress‐strain behavior, the samples obtained at 230 and 275 °C showed apparently double yielding behavior. It was suggested that the double yielding points were morphology‐dependent. The first one was the result of the yielding of PE at low strain, and the second one was caused by the yielding of the PC fibers. Moreover, it is the frictional force in the interfaces between PC and PE that transferred the stress to the PC fibers, hence giving rise to the reinforcement of PE by PC.

Stress‐strain curves of PC/PE blends injection molded at various temperatures showing first (I) and second (II) yielding points.     

Synthesis and Characterization of Hyperbranched Poly(β‐ketoester) by the Michael Addition

Summary: A novel hyperbranched poly(β‐ketoester) was synthesized from 2‐(acetoacetoxy)ethyl acrylate by the Michael addition in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as catalyst. ¹H NMR integration experiments revealed that the degree of branching in the poly(β‐ketoester) was remarkably high at a level of 82.9%. The number‐average molecular weight of the polymer was between 2 100 and 12 000 and increased with reaction temperature and conversion.

Synthesis of hyperbranched polymer by Michael addition of AAEA.