Processing characteristics and structure development in solid-state extrusion of bacterial copolyesters: Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The bacterial copolyesters poly(3-hydroxybutyrate-co-3-hydroxyvalerate) have been successfully commercialized by ICI and are currently being distributed worldwide. Because of their bacterial origin, they are completely biodegradable. This has opened up numerous opportunities to develop new environmentally friendly products. The solid-state extrusion of a series of biodegradable copolyesters (P(3HB-3HV)) was performed in our laboratory with the aim of gaining fundamental understanding about their processability below their melting temperatures. The extrudability windows were found to span the temperature range from 135 to 150°C, depending on the composition of the samples under our experimental setup. The solid-state extrudates were found to exhibit an extra melting endotherm about 15–20°C above their normal melting temperature. This high temperature melting peak increasingly became dominant at lower extrusion temperatures. Wide angle X-ray diffraction studies did not indicate any phase change that might be responsible for this increase in the melting point. Contrary to the expectations, the solid-state extruded samples did not show significant chain orientation along the extrusion direction. This might be a result of fracture of the mass in the barrel into smaller pieces and their randomization during the course of their passage through the die. When the extrusion temperature was raised closer to the melting temperature, the quality of the extrudates was improved, and this was reflected in improvement of their mechanical properties. © 1996 John Wiley & Sons, Inc.     

Thermal properties of a tough,new semicrystalline polyimide

Thermal properties of a new semicrystalline polyimide synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride ( BTDA ) and 2,2-dimethyl-1,3-(4-aminophenoxy)propane ( DMDA ) have been studied. Heat capacities in the solid and liquid states of BTDA - DMDA have been measured. The heat capacity increase at the glass transition temperature (T_g = 230°C) is 145 J/°Cmol for amorphous BTDA - DMDA . The equilibrium heat of fusion of the BTDA - DMDA crystals has been obtained using wide-angle X-ray diffraction and differential scanning calorimetry measurements, and is 75.8 kj/mol. Based on the information on crystallinity and the heat capacity increase at T_g, a rigid amorphous fraction is identified in semicrystalline BTDA - DMDA samples, which represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample, which should be associated with crystal sizes, and therefore with crystal morphology. It has also been found that this polymer has a high-temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies of BTDA - DMDA in nitrogen and air are determined to be 154 and 150kJ/mol, respectively.     

Push–pull extrusion: A new approach for the solid-state deformation illustrated with high density polyethylene

The crystalline state deformation of high density polyethylene has been examined at an extrusion draw ratio of 30 over a range of temperatures and pressures. The experiments involve combined pushing (extrusion) and pulling through a conical die. The pressure dependence of the extrusion rate through conical dies is given by a logarithmic relation and the temperature dependence by an activation energy of ～95 kcal/mole. An equation established for the total applied force linearly relates the pulling and extrusion pressure components and represents a force balance at the die entrance and exit. Steady-state extrusion, with or without pulling, was feasible in a pressure range beyond which fractures occurred owing to strain rate and shear or tensile failure. Under some circumstances the extrusion rate was increased by ten times. The mechanical properties and mode of deformation were not affected by pull load and fibers with a tensile modulus of 55 GPa were produced at T < 110°C.     

Microscopic surface and bulk morphology of semicrystalline poly(dimethylsiloxane)–polyester copolymers

In this study, two series of semicrystalline poly(dimethylsiloxane) (PDMS)–polyester segmented copolymers with various PDMS contents were synthesized. One series was based on polybutylene adipate (PBA) as the polyester segment and the other was based on a polybutylene cyclohexanedicarboxylate ester (PBCH) segment. The copolymers were characterized using ¹H‐nuclear magnetic resonance, size exclusion chromatography, dynamic mechanical analyses, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). The microscopic surface morphology and the microscopic bulk morphology were investigated using atomic force microscopy (AFM) and transmission electron microscopy, respectively. The effects of the polyester type and the PDMS content on the crystallinity degree as well as the copolymer surface and bulk morphology at room temperature were investigated for each series. DSC and WAXD results showed the ability of the copolymers to crystallize, to various degrees, depending on the polyester type and the PDMS content. The results showed that the PDMS content had a greater influence on the crystallinity degree in the PDMS‐s‐PBCH (cycloaliphatic) copolymer series than in the PDMS‐s‐PBA (aliphatic) copolymer series. In the copolymers with a low PDMS content, the AFM images showed spherulitic crystal morphology and evidence of PDMS nanodomains in between the crystal lamellae of the ester phase on the copolymer surface. A heterogeneous distribution of the PDMS domains was also observed for these copolymers in the bulk morphology as a result of this segregation between the polyester lamellae. All the copolymers, in both series, showed microphase separation as a result of the incompatibility between the PDMS segment and the polyester segment. Three types of surfaces and bulk morphologies were observed: spherical microdomains of PDMS in a matrix of polyester, bicontinuous double‐diamond type morphology, and spherical microdomains of polyester in a matrix of PDMS as the PDMS content increases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Processing aids for mixing and extrusion of silica–natural rubber compounds

This paper explores the use of silica as a major component, 67% and 100%, of total filler content in natural rubber, carbon black being the minor component. In order to overcome the mixing difficulty, a coupling agent was used. A previous study dealt with the causes of difficulty in extruding high-silica and all-silica compounds. A premature reaction of the coupling agent with natural rubber resulted in wavy extrudates. In the case of a 100% silica compound, the filler dispersion and distribution were not satisfactory in spite of the presence of the coupling agent. The compound was too stiff to be extrudable. In the present work, metal carbonates were added to the formulation. They included calcium, zinc, magnesium, and lead carbonates. These additives significantly facilitated the incorporation, distribution, and dispersion of the filler. The resulting compounds were soft enough to be extruded. The extrudate surfaces were smooth to slightly wavy. Decreasing the amount of the coupling agent to 75% of the original recipe still allowed the compounds to be extruded, although the waviness of the extrudates increased somewhat.     

Processing characteristics of alpha-methylstyrene–methacrylonitrile copolymer

Processing behavior of alpha-methylstyrene–methacrylonitrile copolymer has been studied in a Brabender Plasticorder and in a capillary rheometer. The copolymer is thermally unstable at a processing temperature of 230°C; however, addition of 2% ethyl acrylate to the copolymer composition enhances processing stability. The terpolymer is processable in the range of 210° to 250°C. However, it is limited by melt fracture at low shear rates.     

Influences of liquid electrolyte and polyimide identity on the structure and conductivity of polyimide–poly(ethylene glycol) materials

Current fuel cell technology demands improvements for widespread use, and novel polymer materials may be able to achieve the necessary enhancements. This work inspects the composition, structure, and properties of poly(ethylene glycol) (PEG)–aromatic polyimide systems aimed at polymer electrolyte membrane applications, as PEG is a known ion conductor and aromatic polyimides are quite stable. Liquid electrolytes were incorporated into the polymers through soaking to achieve ionic conductivity. By varying polyimide and liquid electrolyte, the polymers were analyzed for their structure and conductivity. Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small‐angle X‐ray scattering, electrochemical impedance spectroscopy, and cyclic voltammetry were used as characterization tools. Electrolyte identity impacts liquid uptake and conductivity. Polyimide identity can influence the size and variability of the doped polymer structure, which ultimately can change conductivity by up to 28%, with the maximum conductivity being 102 mS/cm at 80°C and 70% RH. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41675.     

Magnetic (ethylene–octene) elastomer composites obtained by extrusion

Most research on magnetorheological elastomer (MRE) composites is focused on achieving the best magnetic and magnetorheological properties of composites. Less attention is paid to obtain adequate strength properties. The aim of this study was to receive MRE composites with the best mechanical characteristics. Thermoplastic ethylene–octene rubber composites, filled with different magnetoactive particles were reported. The use of extrusion method instead of traditional preparation processes (two‐roll mill, mixer) of composites was also presented. Ferromagnetics: micro‐ and nano‐sized iron oxides, as well as gamma iron oxide and carbonyl iron powder were found to be an active fillers improving both mechanical and magnetic properties of rubber. Application of extrusion process affected mechanical properties of MRE composites and the dispersion of magnetic fillers. Dynamic mechanical analysis (DMA) indicates the presence of strongly developed secondary structure in vulcanizates. Studies investigated by vibration sample magnetometer (VSM) proved that all composites exhibit adequate magnetic properties, predispose them for plenty of applications with the most promising being nowadays tunable vibration absorbers. POLYM. ENG. SCI., 57:520–527, 2017. © 2016 Society of Plastics Engineers     

Processing characteristics,structure development,and properties of uni and biaxially stretched poly(ethylene 2,6 naphthalate) (PEN) films

Poly(ethylene 2,6, naphthalene dicarboxilate), PEN, is very similar to poly(ethylene terephthalate), PET, in its chemical structure and was, therefore, expected to exhibit similar processing characteristics. We, however, observed a few problems during stretching of PEN, the most important of which was necking behavior at 145°C, which is between T_g (117°C) and T^cc (195°C). This is usually observed in PET only when it is stretched close to or below T_g. At temperatures between T_g and T_cc (cold crystallization temperature) PET stretches rather uniformly. The temperature window for film stretching appears to be rather wide, but our results indicate that this is not the case. Films stretched to high stretch ratios become uniform due to propagation and final disappearance of necks as a result of stress hardening. Our attempts at stretching these films at higher temperatures indicated that necking is eliminated, but so is stress induced crystallization, which causes stress hardening (unless high stretching rates are employed). The presence of stress hardening is essential for obtaining high quality, uniform films of these polymers. In addition, at high temperatures thermally activated crystallization which starts dominating the structure development, detrimentally affects the general appearance of the films. In brief, the PEN films we investigated have a narrower processing window than was anticipated based on their thermal behavior alone. At elevated temperatures the films are sensitive to the rate of stretching even more than typical PET processed at comparable conditions. The uniformity of the films depends on the stretch ratio, stretching mode, ratio(s) and rates and temperature. WAXS studies on the films indicate that the macromolecules packed into the low temperature crystal modification. In addition, WAXS pole figure studies suggest that naphthalene planes preferentially orient parallel to the film surface during biaxial stretching. The biaxially stretched films were observed to exhibit a bimodal chain orientation as evidenced by pole figure analysis of the (010) planes.     

Microcellular and nanocellular solid-state polyetherimide (PEI) foams using sub-critical carbon dioxide I. Processing and structure

In this study we investigate the solid-state batch foaming of polyetherimide (PEI) using sub-critical CO₂ as a blowing agent. We report on the gas diffusion for various saturation pressures in this system. Foaming process characterization is reported detailing conditions used to create microcellular and nanocellular PEI foams of 40% and higher relative density. Gas sorption, foaming, and resultant morphologies are analyzed and compared to previously reported results on PEI thin films. It was found that equilibrium gas concentrations for PEI sheet begin to significantly exceed that of films for CO₂ pressures above 3 MPa. A large solid-state foaming process window has been identified that allows for the creation of either microcellular or nanocellular structures at comparable density reductions. A transition from micro-scale cells to nano-scale cells was observed at gas concentrations in the range of 94–110 mg CO₂/g PEI. Additionally, a hierarchical structure was observed which consisted of nanocellular structures internal to microcells. The PEI–CO₂ system offers the unique opportunity to compare and contrast the bulk properties of nanofoams and microfoams.     

Improvement of blown film extrusion of poly(Lactic Acid): Structure–Processing–Properties relationships

The blown extrusion of poly(lactic acid) (PLA) presents several challenges mainly due to the poor shear and elongation properties of this biopolymer. This article highlights some promising routes to enhance the processability of PLA for blown extrusion. To achieve this objective, various formulations of PLA with multifunctionalized epoxy, nucleating agents, and plasticizer were elaborated and studied on the basis of their linear viscoelasticity and elongational properties. We further characterized both the structure and thermomechanical properties of blown films produced with these PLA formulations. Stability charts for the film blowing of neat and modified PLA were thus established at different processing conditions. On the basis of these results, we managed to achieve a large enhancement of the blown processing windows of PLA with high blow‐up ratio (BUR) and take‐up ratio attained. We were able to demonstrate that a higher kinetic of crystallization can also be reached for chain‐extended and branched PLA formulated with adequate amounts of nucleating agents and plasticizers. Induced crystallization during process was also demonstrated. Through this work, blown films with interesting thermomechanical and mechanical properties have been elaborated using an optimal formulation for PLA. POLYM. ENG. SCI., 54:840–857, 2014. © 2013 Society of Plastics Engineers     

Phase structure,morphology and phase boundary diagram in an aromatic polyimide (BPDA–PFMB)/m-cresol system

An organo-soluble aromatic polyimide has been synthesized from 3,3′, 4,4′-bis(phenyltetracarboxylic) dianhydride (BPDA) and 2,2′-bis (trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) via a one-step polymerization in m-cresol. The phase boundary diagram for this system has been established by differential scanning calorimetry, polarized light microscopy (PLM) and wide angle X-ray diffraction (WAXD) experiments. A crystallosolvate form I has been found over the entire concentration region at low temperatures. When the temperature is increased, an isotropic phase has been observed below concentrations of about 40%. In the relatively high concentration region between 45 and 95%, a transition from the crystallosolvate from I to a crystallosolvate form II has been observed. Form II exhibits a different WAXD pattern. In a narrow concentration region between the isotropic and the crystallosolvate form II (40–45%), a biphase behavior has been found. The birefringence of this region may be an indication of a liquid crystalline phase. The BPDA–PFMB polymer crystal has been found in the very high concentration region (>95%) for temperatures >250°C. The morphologies of these phases have been investigated via PLM and transmission electron microscopy. Above the gel/sol transition temperature, the form I shows negative birefringent spherulites consisting of thin lamellae. The form II exhibits a tendency of positive birefringent spherulites. Possible mechanisms of the formation of the metastable phase morphology and their associations with the mechanical gel/sol transition are also discussed.     

Processing,structure, and properties of multiwalled carbon nanotube–poly(phenylene sulfide) composite fibers

To improve the processability and properties of the poly(phenylene sulfide) (PPS) fibers at room temperature and high temperatures, a series of composite fibers based on PPS and multiwalled carbon nanotubes were prepared by melt spinning. We researched the processability with a high‐pressure capillary rheometer, and the properties of the composite fibers were investigated in detail by scanning electron microscopy, differential scanning calorimetry, fiber sonic velocity measurement, and single‐fiber strength testing. The results show that the carbon nanotubes (CNTs) had good interfacial adhesion with PPS and dispersed homogeneously in the PPS matrix. When the shear rate was higher than 500 s^?1, the oriented CNTs induced the orientation of PPS molecular chains; this resulted in a decline in the apparent viscosity and an increase in the orientation degree of the molecular chains. Meanwhile, the CNTs acted as nucleating agents to effectively improve the crystallization of PPS. The strength of the fibers at room temperature were improved by 28.8% after the addition of 0.2% CNTs, and the initial modulus was also significantly enhanced. The strength retention at 160 °C was promoted from 60.58 to 88.32% with the addition of 1.0% CNTs. The shrinking percentage decreased to almost zero from higher than 15%; this suggested that the CNTs could efficiently improve the dimensional stability at high temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44609.     

Effect of ultrasound on extrusion of polypropylene/ethylene–propylene–diene terpolymer blend: Processing and mechanical properties

The effects of ultrasonic irradiation on extrusion processing and mechanical properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) blends are examined. Results show that appropriate irradiation intensity can prominently decrease die pressure and apparent viscosity of the melt, increase output, as well as increase toughness of PP/EPDM blends without harming rigidity. In case the blends are extruded with ultrasonic irradiation twice, the impact strength of the blend rises sharply at 50–100 W ultrasonic intensity, and amounts to more than 900 J/m, 1.5 times as high as that of blend without ultrasonic irradiation. Scanning electron microscopy observation shows that with ultrasonic irradiation, morphology of uniform dispersed EPDM phase and good adhesion between EPDM and PP matrix was formed in PP/EPDM blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3519–3525, 2003     

Modification of poly(lactic) acid by reactive extrusion and its melt blending with acrylonitrile–butadiene–styrene

Poly(lactic) acid (PLA) is a biodegradable polymer that has attracted interest as a potential substitute for some thermoplastic polymers. However, its advanced brittleness at room temperature represents one of the major drawbacks for its general use. In this work, PLA was modified by reactive extrusion (PLA_REx) to enhance the rheological behaviour and to limit its degradation. The modified material was melt blended with acrylonitrile–butadiene–styrene (ABS), and the resultant morphology, rheological, thermo‐mechanical and fracture behaviour were analysed. Since PLA does not have reasonable compatibility with ABS, maleic‐anhydride‐grafted ABS (ABS‐g‐Ma) was used as compatibilizer. The morphology of the PLA_REx/ABS samples resulted in the formation of small ABS rods in the matrix. The presence of maleic anhydride contributed to reducing the interfacial energy of the blends and to obtaining finer micro‐domains of the ABS‐rich phase in the PLA_REx matrix. In the compatibilized blends, the presence of elongated ABS‐rich phases opposed free crack propagation and contributed to the increase in fracture energy in comparison to neat PLA. © 2020 Society of Chemical Industry     

The effect of preparation process of PMDA–ODA–DR1 polyimide on its second harmonic generation characteristics

In situ second harmonic generation (SHG) observation of PMDA–ODA–DR1 polyimide films prepared by different preparative procedures were studied to understand the effects of the residual acid and the imidization byproduct and the extent of imidization on the SHG characteristics of the PMDA–ODA–DR1 polyimides. PMDA–ODA–DR1 polyimides with or without removal of salt were also investigated to study the influence of remaining triethyl hydrogen ammonium chloride salt on the SHG characteristics and reliability of the polymers. A blue shift in the UV/vis spectrum during poling was observed for the low temperature-baked film, but did not occur for the high-temperature-baked film. Both high temperature imidization and removal of the byproduct organic salt did not only improve the poling efficiency of PMDA–ODA–DR1 polyimide as a SHG material, but also slowed down the relaxation of the film and made the film more reliable. © 1995 John Wiley & Sons, Inc.     

Study of P(AM‐NVP‐DMDA) hydrophobically associating water‐soluble terpolymer

A new kind of hydrophobically associating water‐soluble terpolymer P(AM‐NVP‐DMDA) was synthesized by free radical terpolymerization. Compared with micellar terpolymerization, this terpolymerization can be conducted in aqueous solution in absence of external surfactant, because the hydrophobic monomer is surface active. Synthesis, structure, and solution properties of P(AM‐NVP‐DMDA) terpolymer were studied, including its electrolyte effect, rheological behavior, temperature dependence of viscosity, dilute solution property, and the polymer–alkali, polymer–surfactant interaction. The terpolymer shows strong hydrophobic effect, and the terpolymer aqueous brine solution exhibits high viscosity at low polymer concentration. Incorporation of N‐vinyl‐pyrrolidone into the terpolymer causes an improvement in thermal stability of the terpolymer. The transmission electron photomicrograph analysis of the terpolymer indicates that the presence of the microphase separation of the terpolymer in aqueous solution plays an important role in the viscosification efficiency of the terpolymer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 211–217, 1999     

Amplitude–frequency characteristics of polymer electro‐magnetic dynamic tri‐screw extrusion

The mechanism of plastic forming and processing in electromagnetic dynamic tri‐screw extruder is very sophisticated and the investigation of amplitude–frequency characteristic acts as the foundation of equipment design and the optimization of polymer processing parameters. A mathematical and analytical model of plastic forming in such extruder was developed and the results were nondimensional‐normalized. To validate the mathematical solutions experiments based on LDPE were carried out and the experimental vibration amplitude and vibration frequency curve was obtained. Three conclusions can be drawn herein: (1) the experimental results hold a good agreement with the calculations, and thus the feasibility of the proposed model is validated; (2) the possibility of resonance closely relates to polymer melt viscosity, rotating speed, and geometry parameters of the screw; (3) resonance of the tri‐screw extruder is seldom observed under normal conditions and there exists an inverse correlationship between vibration frequency and amplitude. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122:1778–1784, 2011     

Microwave irradiation of nadic-end-capped polyimide resin (RP-46) and glass–graphite–RP-46 composites: cure and process studies

Microwave energy was investigated to cure nadic-end-capped polyimide precursors (RP-46 resin) using a Cober Electronics Model LBM 1.2A/7703 microwave oven at a frequency of 2.45 GHz. Both neat resin samples and glass cloth and hybrid glass cloth–graphite cloth–RP-46 resin composites were studied. For the resin studies, the effect of various parameters, such as power level, sample size, processing temperature, time, and graphite fiber absorber, were investigated. The variables investigated with the composite study were the power level, mold material, vacuum, and low pressure. The results showed that microwave energy was effective in curing both neat resin samples and composite specimens. The presence of a small quantity of absorber (chopped carbon fiber) accelerates the cure dramatically. Moreover, soapstone mold material was found to be an efficient absorber for glass and glass–graphite composite processing, causing an effective cure in less than 1 h. Glass and glass–graphite hybrid composites with flexural strengths of 372–588 MPa (54–85 ksi) and moduli of 28.7–31.7 GPa (4.2–4.6 Msi) have been fabricated. This is equivalent to 50 to 80% of the properties of composites fabricated by conventional means. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2391–2411, 1999