Polyetherimide Foams Research Articles

Dimensional Accuracy Control and Compressive Property of Microcellular Polyetherimide Honeycomb Foams Manufactured by an In Situ Foaming Fused Deposition Modeling Technology

The microcellular honeycomb foams can be manufactured via fused deposition modeling (FDM) technology. However, the process often involves complicated pre/post‐treatment. Herein, a novel in situ foaming FDM technology is developed to efficiently fabricate the microcellular polyetherimide (PEI) honeycomb foams with various lattice structures. The extremely low gas diffusivity endows the CO2‐saturated PEI filament with a long‐time printing ability and well printing performance, which is characterized by a long printable time up to 7 days and the formation of microcellular structure within the deposited foam strands. The printed PEI foam parts possess high dimensional accuracy with a relative accuracy (δR) of 1.3–6.4% at the external regions and low internal accuracy with δR of 27.5–48.8%, resulting from the increased nozzle expansion and reduced melt viscosity. An accuracy correction based on the nozzle expansion is effective to improve the dimensional accuracy of the foam parts. The high accuracy control of macro/microstructure and the advantages of green processing and long‐time printing make the in situ foaming FDM technology show great application prospects in the fabrication of hierarchical cellular materials.

High‐Performance Polymer Foams by Thermally Induced Phase Separation

Macroporous, low-density polyetheretherketone, polyetherketoneketone, and polyetherimide foams are produced using a high-temperature, thermally induced phase separation method. A high-boiling-point solvent, which is suitable to dissolve at least 20 wt% of these high-performance polymers at temperatures above 250 °C, is identified. The foam morphology is controlled by the cooling procedure. The resulting polymer foams have porosities close to 80% with surface areas up to 140 m2 g-1 and elastic moduli up to 97 MPa.

Influence of nucleating agent type on the morphology of extruded polyetherimide foam for printed circuit boards*

This work focuses on the development of foamed high temperature thermoplastic substrates for printed circuit boards. For this application it is necessary to achieve mean cell diameters smaller than 30 µm in order to be able to realize vias and high packaging densities (miniaturization). Different additives as nucleating agents, namely macro- and micro-crystalline talc, silica, calcium carbonate, and wollastonite, were melt-compounded with polyetherimide using a twin-screw extruder. Foamed samples are prepared by foam extrusion using a slit die and CO2 as physical blowing agent. The aim of this study is to analyze the influence of the mean particle size and the particle surface tension on the mean cell diameters. Therefore, the shape of the additives, the foam morphology, and the elongational viscosity were considered. The additives with a suitable particle size and surface tension exhibit a positive influence on the foam morphology, resulting in smaller cell diameters (<30 µm), a narrower cell size distribution and a foam density lower than 900 kg/m3. If the mean particle diameter of the nucleating agents is lower than 0.6 µm in this study, no nucleation effect could be observed. This is related to the fact that no heterogeneous nucleation occurs, if the particle diameter is too small. If the mean particle diameter of the used additives is larger than 1.5 µm, which could be demonstrated in this study in case of polyetherimide, then the additive acts as nucleating agent and heterogeneous nucleation occurs. Furthermore, it was observed that the mean cell diameter was affected by the different surface tensions of the studied nucleating agents.

Studies on thermal degradation kinetics and dielectric properties of polyether imide foam/nanosilica-based nanocomposites

ABSTRACTIn this paper, polyether imide (PEI) having properties such as a high glass transition temperature of 216°C, high heat resistance, high flame resistance, low smoke generation and a high melting point within the range of 400°C, having low thermal conductivity and low dielectric constant was chosen to be a polymeric foam. Water vapor-induced phase separation method was used to prepare PEI foams. PEI foams were reinforced with nano-silica (weight 1, 3 and 5%) in order to alter the dielectric properties, thermal conductivity and degradation kinetics of foamed polymer. The tested samples showed a reduction in dielectric constant than that of solid PEI but at a higher loading, it showed a higher value due to threshold percolation and a reduction in thermal conductivity was observed for foamed PEI. From thermogravimetric analysis, we can conclude that PEI with 3% filler loading showed better thermal stability compared to other PEI foam compositions.

Microcellular polyetherimide/carbon nanotube composite foam: Structure, property and highly reinforcing mechanism

Microcellular polyetherimide (PEI)/carbon nanotube (CNT) composite foams were prepared via water vapor-induced phase separation (WVIPS) process. The hydroxylated multi-wall nanotubes (MWNTs-OH) were applied, and strong interfacial interaction formed with PEI molecules by high grafting ratio. Much PEI resin adhered to MWNTs-OH surface, resulting in an obvious increase of MWNTs-OH diameter and formation of coating structure. For the composite foams, the homogenous spherical-like cell structure can be observed. With increasing MWNTs-OH content, the tensile strength of the composite foam first increased, and then decreased, reaching maximum at 4 wt% MWNTs-OH, a roughly 53% increase as a result of reinforcing effect of MWNTs-OH on matrix. Meanwhile, the storage modulus of the composite foam was much higher than that of pure PEI foam over the temperature range tested and still maintained above 610 MPa at 200 °C, suggesting a remarkable improvement of thermal mechanical stability. MWNTs-OH distributed uniformly in the matrix, and under stress it was pulled out with surface completely wrapped by PEI resin, confirming that the failure mode was the deformation and destruction of non-interface resin. By incorporation of MWNTs-OH, the thermal decomposition temperature, char yield and LOI values of the composite foam increased, while the UL-94 tests were classed as a V-0 rating.

Polyetherimide Foams Filled with Low Content of Graphene Nanoplatelets Prepared by scCO₂ Dissolution.

Polyetherimide (PEI) foams with graphene nanoplatelets (GnP) were prepared by supercritical carbon dioxide (scCO2) dissolution. Foam precursors were prepared by melt-mixing PEI with variable amounts of ultrasonicated GnP (0.1–2.0 wt %) and foamed by one-step scCO2 foaming. While the addition of GnP did not significantly modify the cellular structure of the foams, melt-mixing and foaming induced a better dispersion of GnP throughout the foams. There were minor changes in the degradation behaviour of the foams with adding GnP. Although the residue resulting from burning increased with augmenting the amount of GnP, foams showed a slight acceleration in their primary stages of degradation with increasing GnP content. A clear increasing trend was observed for the normalized storage modulus of the foams with incrementing density. The electrical conductivity of the foams significantly improved by approximately six orders of magnitude with only adding 1.5 wt % of GnP, related to an improved dispersion of GnP through a combination of ultrasonication, melt-mixing and one-step foaming, leading to the formation of a more effective GnP conductive network. As a result of their final combined properties, PEI-GnP foams could find use in applications such as electrostatic discharge (ESD) or electromagnetic interference (EMI) shielding.

Microcellular polyetherimide/graphene‐polysiloxane composite foam: intercalation structure, mechanical and thermal properties

AbstractBased on the industrialized reduced graphene oxide (RGO) product, polyetherimide (PEI)/RGO composite foam was prepared by a water‐vapor‐induced phase separation process by incorporation of polysiloxane (SI) as a compatibilizer. It was found that PEI/SI molecules were intercalated into the RGO layers through strong interfacial interaction and RGO with increased layer thickness was uniformly distributed in the PEI matrix. The composite foam possessed a homogeneous spherical‐like cell structure with narrow cell size distribution and low apparent density. In the range of 0–1 wt% RGO‐SI content, the area under the stress–strain curves increased dramatically, indicating the significantly increased toughness of the composite foam, while the tensile strength reached a maximum of 14.5 MPa at 1 wt% RGO‐SI as a result of the reinforcing effect of RGO‐SI on the foam. The addition of RGO‐SI led to a remarkable increase in Tg. Compared with neat PEI foam, the thermal degradation temperature and char yield of the composite foam clearly increased, while in the range of 0.5–3 wt% RGO‐SI a high storage modulus was maintained at high temperature, reaching about 300 MPa at 200 °C, indicating a remarkable improvement of the thermal mechanical stability of the foam. © 2018 Society of Chemical Industry

Mechanical performance of CF/PEEK–PEI foam core sandwich structures

Previous work showed that thermoplastic composite sandwich structures offer great potential to meet the demands of lightweight structures for aviation applications. In this study, the influence of several processing parameters on the mechanical properties of thermoplastic sandwich components, consisting of carbon fibre reinforced polyetheretherketone skins and polyetherimide foam cores, is characterised. Sandwich specimens are manufactured with varying skin temperatures, core compaction distances and different polyetherimide concentrations at the skin–core interface. Following, sandwich samples are mechanically tested to characterise the bond strength, the core performance as well as the performance of the whole sandwich. The results show that in most cases the processing parameters significantly affect the cell structure of the sandwich core, provided that a proper fusion bond between skins and core exists. Thereby, the core performance seems to be weakened and failure predominantly occurs in the transition between affected and original cell structures.

Influence of polyamide–imide concentration on the cellular structure and thermo-mechanical properties of polyetherimide/polyamide–imide blend foams

The present work considers the preparation of medium-density polyetherimide (PEI)/polyamide–imide (PAI) blend foams by means of water vapor-induced phase separation (WVIPS) and their characterization. While pure polymer foams showed homogeneous cellular structures with average cell sizes of 10–12μm, PEI/PAI blend foams presented two distinctive closed-cell structures depending on the composition of the blend. At the lowest concentration of PAI (25wt%) foams showed a very fine homogeneous microcellular structure with an average cell size of 1.4μm, consequence of good miscibility between both polymers, while at the highest studied concentration of PAI (50wt%) foams presented a dual cellular structure formed by small cells (around 1μm in size) within the walls of considerably bigger ones (22μm in size) due to polymer phase separation. The blend foams presented a thermal decomposition behavior similar to that of pure unfoamed polymers, with the foam with 25wt% PAI showing a slightly higher thermal stability. Furthermore, this particular foam presented an improved specific storage modulus compared to pure PEI foam and to the one with 50wt% PAI. X-ray diffraction (XRD) analysis indicated that no polymer crystallization was induced by foaming.

Graphene nanoplatelets-reinforced polyetherimide foams prepared by water vapor-induced phase separation

The present work considers the preparation of medium-density polyetherimide foams reinforced with variable amounts of graphene nanoplatelets (1–10 wt%) by means of water vapor-induced phase separation (WVIPS) and their characterization. A homogeneous closed-cell structure with cell sizes around 10 µm was obtained, with foams exhibiting zero crystallinity according to X-ray diffraction (XRD). Thermogravimetric analysis under nitrogen showed a two-step thermal decomposition behaviour for both unfilled and graphene-reinforced foams, with foams containing graphene presenting thermal stability improvements, related to a physical barrier effect promoted by the nanoplatelets. Thermo-mechanical analysis indicated that the specific storage modulus of the nanocomposite foams significantly increased owing to the high stiffness of graphene and finer cellular morphology of the foams. Although foamed nanocomposites displayed no further sign of graphene nanoplatelets exfoliation, the electrical conductivity of these foams was significant even for low graphene contents, with a tunnel-like model fitting well to the evolution of the electrical conductivity with the amount of graphene.

Semi-continuous approach for the study of impacts on woven composite laminates: Modeling interlaminar behavior with a specific interface element

This paper investigates impacts on sandwich structures made up of a thin woven composite skin and polyetherimide foam core. A semi-continuous Finite Elements explicit modeling was chosen to represent the response of the woven skin made of plies with different orientations. The plies are modeled with specific woven elements, and are bonded with a new damageable shell-to-shell interface element. The modeling strategy is validated by representing static bending, low velocity impacts and medium velocity oblique impacts. The presented approach is accurate enough to predict the size and the shape of the damage for the woven composite laminate.

Cell morphology and mechanical properties of microcellular mucell® injection molded polyetherimide and polyetherimide/fillers composite foams

ABSTRACTMicrocellular polyetherimide (PEI) foams were prepared by microcellular injection molding using supercritical nitrogen (SC‐N2) as foaming agent. The effects of four different processing parameters including shot size, injection speed, SC‐N2 content, and mold temperature on cell morphology and material properties were studied. Meanwhile, multiwalled carbon nanotube (MWCNT), nano‐montmorillonoid (NMMT), and talcum powder (Talc) were introduced into PEI matrix as heterogeneous nucleation agents in order to further improve the cell morphology and mechanical properties of microcellular PEI foams. The results showed that the processing parameters had great influence on cell morphology. The lowest cell size can reach to 18.2 μm by optimizing the parameters of microcellular injection molding. Moreover, MWCNT can remarkably improve the cell morphology of microcellular PEI foams. It was worth mentioning that when the MWCNT content was 1 wt %, the microcellular PEI/MWCNT foams displayed optimum mechanical properties and the cell size decreased by 28.3% compared with microcellular PEI foams prepared by the same processing parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4171–4181, 2013

Fabrication and characterization of polyetherimide nanofoams using supercritical CO2

Polymer nanofoams have recently attracted significant interest in both industry and academia. The unique nanoscaled porous structure could bring unprecedented material properties that have not been seen in conventional or microcellular polymer foams. It has been hypothesized that nanofoams could have a much higher specific strength and toughness as well as significantly improved thermal resistivity. In this research, we study the fabrication and characterization of polyetherimide nanofoams using a supercritical carbon dioxide foaming process. A process map indicating the conditions to obtain various polyetherimide foam structures, including micro-, micro/nano transition, and nanofoams has been established. Two types of nanofoams were observed, one made with high gas concentrations and the other with high foaming temperatures. The one with high gas concentrations exhibited a higher specific modulus than that of unfoamed polyetherimide. Nanofoams generally showed a higher thermal resistivity than microfoams with similar relative densities. It is found that the equilibrium CO2 concentration in polyetherimide under the supercritical conditions does not fit well to the well-known dual-mode sorption model. A new gas concentration model was developed to describe the CO2 uptake under supercritical conditions.

Indentation into polymeric foams

The effects of the nose shape of rigid indenters on the indentation behaviour of polymethacrylimide (PMI) and polyetherimide (PEI) foams with different densities are investigated. Experimental results show that indentation resistance depends on the geometry of the indenter and the density of the foam. Analytical models based on the deformation mechanisms observed in experiments are developed to predict the indentation resistance. It shows that the analytical predictions are in good agreement with experimental measurements for a range of polymeric foams. This study presents a complete and systematic experimental data on the indentation behaviours of a range of polymeric foams and demonstrates the capability of the analytical model to predict the indentation behaviours of PMI and PEI foams.

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 3MPa. 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 94–110mg 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.