Chemical Foaming Agent Research Articles

Processing of a new class of multifunctional hybrid for electromagnetic absorption based on a foam filled honeycomb

A multifunctional hybrid material class in the form of a sandwich panel has been developed towards the combined optimization of mechanical and electromagnetic absorption performance. The faces of the panel are made of glass fibre reinforced epoxy composites and the core is made of carbon nanotube reinforced polymer foam filling a metallic honeycomb. The different processing strategies and options tested to fabricate the core material are described as well as the associated scientific and technological issues. The most efficient processing route is by foaming the nanocomposite with a chemical foaming agent directly inside the honeycomb. This route offers a good surface finish and the operation can be achieved in one step. But, in order to produce large panels with a semi-continuous process, thermo-mechanical insertion of the foamed nanocomposite with supercritical CO2 can be more suitable. The characterization of the electromagnetic absorption of the panels produced by different routes shows that the performance is not much sensitive to processing defects making possible upscaling to mass production.

Morphological analysis of microcellular PP produced in a core‐back injection process using chemical blowing agents and gas counter pressure

A complete experimental analysis of the microcellular injection process using Chemical Blowing Agents (CBA) with Gas Counter Pressure (GCP) and core‐back expansion is presented. Three different types of polypropylene, neat and charged, were mixed with two different CBAs and injected into a plate mold with varying process parameters. First, an exhaustive cartographical mapping of the plate morphology is analyzed. In a second step, the relation between injection parameters and the resulting morphology is investigated. The results show that injection time affects the cellular structure. The formulation, especially the type of chemical foaming agent, controls the average bubble radius. Compared with classical injection process, the use of CBAs, combined to Gas Counter Pressure and core‐back process, allows obtaining parts with good surface aspect, more homogeneous cellular structures and smaller bubble radius. POLYM. ENG. SCI., 55:2465–2473, 2015. © 2015 Society of Plastics Engineers

Experimental study on micro-porous patterning using UV pulse laser hybrid process with chemical foaming agent

A new micro porous patterning method was proposed in this paper. We experimentally demonstrated the feasibility of this method using UV laser hybrid process with polymer sheet. The PP(Polypropylene) sheet of 0.1mm thickness was firstly mixed with CFA(Chemical Foaming Agent), and then the desired porous pattern was selectively fabricated by 355nm UV pulse laser processing. According to processes parameters such as laser fluence, processing time and CFA density, the characteristic of porosity which is pore size, pore density and pore type was proven to be controllable. From these experimental results, it was possible to manufacture micro porous patterned polymer sheet.

Sidoarjo Mud-Based Lightweight Mortar Using Foaming Agent and Aluminum Powder

Lightweight concrete is generally used particularly at high-rise buildings in order to reduce the risk of earthquake. It is common that lightweight concrete is made with less Portland Cement associated with pozzolanic material as a binder. In this paper, calcined-Sidoarjo mud was identified as pozzolanic material as cement substitution. The mud contains SiO2, Al2O3 and Fe2O3 and to be expected it has properties as a potential pozzolanic material. Paste and mortar as specimens made from mixtures of calcined-Sidoarjo mud, fly ash, lime, portland cement and natural sand. The specimens were then mixed with a commercial chemical foaming agent and Aluminum powder as aerating agents. The results showed that test paste specimens using chemical foam showed higher compressive strength and density than those of using aluminum powder. Lightweight paste made with chemical foam has compressive strength of 10.7 Mpa with density of 1133kg/m3. Moreover, the specimens of lightweight mortar had the compressive strength of 4.8 MPa, and the density of 1154.7kg/m3. Lightweight paste specimens using aluminum powder had a compressive strength of 2.8 Mpa with density of 1013kg/m3, while lightweight mortar specimens showed compressive strength of 2.4 MPa, and the density was 966kg/m3.

Chemical foaming extrusion of poly(lactic acid) with chain-extenders: Physical and morphological characterizations

The effects of an epoxide-based chain-extender (CE) on the properties of poly(lactic acid) (PLA) foams obtained by chemical foaming extrusion using 4wt.% of chemical foaming agent (CFA) were studied. PLA/CE blends with different weight ratios of CE were initially processed using a co-rotating twin-screw extruder. PLA/CE foams were then produced using a single-screw extruder. Various PLA/CE foams characterizations, including solution viscosity, thermal properties (DSC, TGA), cellular structure (void fraction, cell size, open cell content), mechanical and dynamic rheological behaviors, were investigated. Results show that the addition of CE enhances the viscosimetric average molecular weight and rheological properties (viscosity and storage modulus) of PLA, but it has no significant effects on the thermal properties of PLA, except the occurring of a cold crystallization. The CE incorporation also led to a decrease in the void fraction of cellular PLA, in the cell size and in the open cell content and to an increase in the cell density. Furthermore, the tensile mechanical properties such as yield stress and elongation at break of cellular materials increased with the addition of CE.

Mix design, properties and cost analysis of fly ash-based geopolymer foam

This study has investigated the joint effect of several mix parameters on the properties of foam geopolymers. The mix parameters analysed through a laboratory experiment of 54 different mortar mixes were, sodium silicate/sodium hydroxide mass ratio (2.5, 3.5, 4.5), activator/binder mass ratio (0.6, 0.8, 1.0), chemical foaming agent type (hydrogen peroxide (H2O2) and sodium perborate (NaBO3)) and foaming agent mass ratio content (1%, 2%, 3%). Properties, SEM and FTIR analysis and cost analysis are included. The results show that the sodium perborate over performs hydrogen peroxide leading to a lower overall thermal conductibility of foam geopolymers. Mixtures with a low thermal conductivity of around 0.1W/(m·K) and a compressive strength of around 6MPa were achieved. The cost analysis show that the foaming agents are responsible for a small percentage of foam geopolymers total cost being that the alkaline activators are responsible for more than 80%.

Effect of melt viscosity on the cell morphology and properties of poly(lactic acid) foams

A compression molding foaming technique was used to prepare polylactic acid foams with a chemical foaming agent. The effect of melt viscosity of the polylactic acid on its cell morphology, apparent density, void fraction, cell population density, cell diameter, mechanical properties, and thermal property were studied. The apparent density of the foamed polylactic acid first decreased with decreasing melt viscosity and then increased, whereas the void fraction showed an opposite trend. A lower melt viscosity resulted in smaller cells, a more uniform cell size distribution, and a higher cell population density until the viscosity could not support further cell expansion which subsequently could cause gas escape and cell collapse. The tensile strength of the foams first increased with decreasing melt viscosity and then decreased. Their impact strength and flexural strength were improved by decreasing the melt viscosity. The use of glycidyl methacrylate only showed a small influence on the thermal stability of foamed polylactic acid.

Experimental investigation on mechanical properties of extruded foamed PVC‐wood composites reinforced with continuous glass fibers

In this study, mechanical performances of extruded foamed and unfoamed PVC‐wood composites, reinforced with continuous glass fibers, were investigated. A specially designed die was used to incorporate the continuous glass rovings into the extruded rectangular shaped profiles. The experimental variables were the number of continuous glass rovings (0–2‐4) and the presence or absence of the chemical foaming agent. Three point bending tests as well as density measurements were conducted to evaluate the mechanical properties and density reduction upon foaming. The results showed that the flexural strength of the reinforced profiles was significantly increased, as 58% increase in flexural strength was noticed for wood plastic composites (WPCs) reinforced with four glass rovings. The highest density reduction (14%) was observed upon foaming for profiles reinforced with four glass rovings, while resulting in strength deterioration. Moreover, results revealed the remarkable effect of reinforcement on preserving mechanical performance of the foamed samples, as 88% increase in flexural strength of the foamed samples reinforced with four glass rovings was observed compared with the unreinforced foamed ones. For the foamed WPCs reinforced with even two glass rovings, the higher specific strength values were also noticed compared to the unreinforced and unfoamed samples. POLYM. COMPOS., 37:1674–1680, 2016. © 2014 Society of Plastics Engineers

Lightweight Medium-Sized Parts Made of Foamed HDPE Processed via Extrusion Blow Moulding: Analysis of Parison Formation

The manufacturing of medium-sized hollow parts using a foamed high density polyethylene was studied using a conventional accumulator blow extrusion machine and a systematic capture of pictures during the parison formation. To fully monitor the parison formation, several experiments were carried out varying the chemical foaming agent content from 0 wt.% to 2 wt.% and increasing the push extrusion speed. Results pointed out greater wall thickness, diameter, and length of parisons with higher weight percentage of blowing agent and extrusion speed. A full experimental characterisation of parison dimensions was essential to assure a proper prediction of the blowing step. Information was used as input for modelling and simulations of the blowing phase of an industrial container. To validate the proposed methodology, a blow moulding process of a generic container was simulated using Ansys Polyflow v13 software and its finite element analysis which provided an accurate approximation of the wall thickness expected. Further real tests on the simulated container also demonstrated that, in those parisons with a 1 wt.% CFA concentration and higher blowing pressure, there was remarkable improvement on their packaging properties such as decreasing of the total weight of the container and an enhancement of its surface quality.

Influence of foam agent content and talc filler on the microcellular and mechanical properties of injection molded polypropylene and talc filled polypropylene composite foams

In this study, influence of the chemical foaming agent content and talc mineral filler on the microcellular and mechanical properties of pure polypropylene and 20 wt% talc filled polypropylene composite foams was investigated. The chemical foaming agent at 1 wt% and 2 wt% ratios was added to pure polypropylene and talc filled polypropylene composites. Using an injection molding machine, foam materials were produced under a set of process parameters consisting of injection pressure, injection speed, melt temperature, and packing pressure. For each set of process parameters, the cell number, cell size, distance between cells, skin layer thickness, cell density, and the mechanical properties of foam products were recorded. The results indicate that the cell number, cell density, skin layer thickness, tensile strength, and tensile modulus values for microcellular talc filled polypropylene composite foam are higher, while the cell diameter, impact strength, and elongation at break values are lower than that of pure microcellular polypropylene foam.

Cell morphology, bubbles migration, and flexural properties of non‐uniform epoxy foams using chemical foaming agent

ABSTRACTEpoxy foams with different densities and microstructures were prepared by changing the process parameters including the foaming temperature, chemical foaming agent (CFA) content and precuring extent. The microstructure of foams reveals a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher precuring extent. However, the cell size and distribution are not affected by the foaming temperature and CFA content without precuring process. In addition, the bubbles migration, which resulted in non‐uniform cell density distribution, was promoted by increasing the foaming temperature and depressed by increasing the CFA content and precuring extent. The flexural properties of the non‐uniform epoxy foams were also studied. Results showed that the flexural modulus was related to the cell morphology, while the flexural strength was affected by both the cell morphology and the position of the specimens during test. It was also found that the relative flexural modulus and strength exhibited a power‐law dependence with respect to the relative density. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41175.

Novel lightweight foamed poly(lactic acid) reinforced with different loadings of functionalised Sepiolite

Abstract The aim of the present work is to develop an ease processable novel biobased lightweight material with improved mechanical and thermal properties. Sepiolite was used as reinforcement to improve Poly lactic acid (PLA) mechanical properties. Composite materials were obtained by extrusion and injection moulding. A chemical foaming agent (CFA) was introduced at 2 wt.% not only to produce a foamed polymer but also to ease the processability of the material. The obtained results demonstrated that Sepiolite improves PLA mechanical properties and makes the composite thermically more stable. The combination of CFA and Sepiolite favours nucleation during the foaming process and therefore the homogeneous formation of microporosity. The appropriate combination leaded to a decrease in density of 33% respect to raw PLA with improved mechanical properties attaining a material 9% stiffer with 10 wt.% Sepiolite and 38% tougher with just 2 wt.% of Sepiolite.

A comparison between different foaming methods for the synthesis of light weight geopolymers

Foaming to reduce the density of geopolymeric materials is increasingly being reported in the literature as it has been shown to be effective in improving their insulating properties. However, there is no consistency in foaming methods and as such this study was performed to compare methods in order to better understand their effect on the properties of geopolymers. A surfactant and two chemical foaming agents (hydrogen peroxide and aluminium powder) were added to a fly ash based geopolymer matrix. Surfactant was also combined with each of the chemical foaming agents in order to stabilise the foam in the geopolymer matrix and to reduce coarse pores. The physical, mechanical and microstructural properties of the low density geopolymers are presented and the effects of the foaming agents׳ characteristics on the hardened product is discussed, as well as the relative merits of the different procedures to synthesise the foamed geopolymer. It was found that homogeneous microstructures with small pores can be obtained by adding surfactant and hydrogen peroxide. The combination of hydrogen peroxide (0.1wt%) and surfactant (1.0wt%) produced geopolymer foams with density and compressive strength values of 0.94g/cm3 and 4.6MPa, respectively.

Clariant foaming agents reduce mass in interior auto parts

The Masterbatches business unit of Clariant has commercialized a new generation of Hydrocerol® chemical foaming agents (CFAs) [see also ADPO, February 2011 and July 2001]. The new CFA masterbatches are designed particularly to help automotive manufacturers reduce the mass of many plastic interior car parts without adversely affecting their appearance or performance. Hydrocerol technology is standardized globally, with production in North America, Europe and Asia, backed by local technical support.

Physical and mechanical properties of foamed HDPE/wheat straw flour/nanoclay hybrid composite

In this study, the effects of Azodicarbonamide (AZD) and nanoclay (NC) content on the physico-mechanical and foaming properties of HDPE/wheat straw flour (WSF) composites were investigated. To meet this objective, AZD as the exothermic chemical foaming agent (CFA) with 3 levels of 0, 2 and 4phr (per hundred parts of resin) and three NC levels of 0, 2, and 5phr were used. The amount of WSF was fixed at 40phr for all formulations. First, the WSF, HPDE, NC and AZD were compounded under the foaming agent decomposing temperature in an internal mixer (HAAKE) and microcellular closed cell foamed samples were prepared using an injection molding machine in a batch foaming process. The cellular structure results showed that by increasing the AZD content from 2 to 4phr, the average cell size and cell density increased whereas the foam density showed a decrease to 21.7% and by adding NC up to 5phr, the cell size decreased and the cell density increased. When the contents of the AZD increased from 0 to 4phr, the water absorption and thickness swelling of samples increased to 19.3% and 26.5% respectively. The mechanical properties of HPDE/WSF composite were reduced by adding the CFA and it was improved by adding 2phr of NC. It should also be noted that the addition of AZD and NC had a negative effect on the foamed composites impact resistance. These results were further supported by SEM micrographs.

The mechanical performance of adhesive joints containing active disbonding agents

A controllable adhesive disbonding mechanism can be achieved by incorporating, and then activating, functional additives located within the matrix of an adhesively bonded joint. This action facilitates the disassembly and material recovery of structurally bonded assemblies.The engineering capabilities of bonded joints containing a range of chemical or physical foaming agents were investigated. Joint disassembly was measured as a function of additive chemistries, physical properties and concentration. The short- and long-term mechanical properties of bonded joints and bulk adhesives containing functional additives were subsequently evaluated.The disbonding mechanism was found to be due to a ‘solid-state foaming’ of the adhesive, followed by a proliferation of micro-cracking throughout the matrix. The effect of the physical foaming agents on joint disassembly was mostly attributable to the volumetric expansion efficiency of the additive whilst constrained within an adhesive matrix. For chemical foaming agents, the effectiveness of disassembly was dependent on the chemical compatibility of the adhesive and additive, the concentration and the efficiency to which the additive decomposed to a gas.

Effect of chemical and physical foaming additives on the properties of PP/wood flour composites

Low weight is an important property of polymer composites used in applications such as construction, the automotive industry, etc. Focusing on fabricating lighter materials, PP/wood flour composites were expanded using different chemical and physical foaming agents. The goal of the investigation was to compare the effect of these additives on the density, mechanical and morphological properties of the expanded composites by means of density determinations, tensile tests and scanning electron microscopy analysis. The foaming agents used were based on azodicarbonamide, sodium bicarbonate and expansive polymer spheres. It was verified that the effect of the chemical foaming agents reflected its degradation behaviour determined by thermogravimetry. Closed cells with varied sizes and more or less regular shapes were found in the materials according to the foaming system used. Among them, Hydrocerol 1004 (a masterbatch of sodium bicarbonate and citric acid in PE), produced the expanded PP/wood flour composites with the finest morphology, significant density reduction and acceptable loss of mechanical properties.

Study on Foam Injection Molding of Thermoplastic Elastomer by Supercritical Fluid

Foam injection molding is a molding method that generates cells in the resin by dissolving carbon dioxide and chemical foaming agent. Foam injection molding makes it possible to reduce weight of products and material by generating cells in the resin. However, this technique may cause a problem defective molded product was a defects known as short-shot if the amount of resin that is filled into the mold is insufficient. Therefore, in this study, we studied to prevent the molding defects such as short shot, and to clarify molding conditions and factors to achieve stable molding process in continuous molding. Foam injection molding with a thermoplastic elastomer and supercritical carbon dioxide was carried out. We considered molding conditions and factors that prevented molding defects such as short-shot and could realize a stable molding process. We have revealed the following results. When carbon dioxide gas was injected at a pressure lower than the critical point, weight of the resin was constant and the weight of the molded product was stable. Therefore, we could achieve a stable molding process, and prevent short-shot. However, in this case, it is necessary to use a gas having a high-solubility into the resin.

Development of poly(lactic acid) cellular materials: Physical and morphological characterizations

The present study aims at assessing the extrusion foaming characteristics of two commercial grades of poly(lactic acid) (PLA) using a chemical foaming agent (CFA). For each PLA the process was optimized based on a maximal void fraction criterion. The extruder die temperature significantly affects the void content (maximal for about 195 °C). An increase in the barrel temperature profile was also correlated with an increase in the void fraction. Moreover an increase in CFA concentration increased the PLA void fraction, and in some cases induced a decrease in cell density and an increase in cell size. Finally, an optimal value of 47% void fraction was obtained. Finally, optimally processed PLAs with varying CFA contents were tensile tested. The results pointed out that it was possible to observe significant decrease in the density and increase in some specific mechanical properties by controlling the extrusion foaming process.

Mechanical properties of injection-molded foamed wheat straw filled HDPE biocomposites: The effects of filler loading and coupling agent contents

This study investigated the effect of filler loading and coupling agent contents on the densities and mechanical properties of injection-molded foamed biocomposites. Biocomposite pellets were manufactured using wheat straw flour, maleic anhydrite grafted polyethylene (MAPE), paraffin wax, and high-density polyethylene (HDPE) with an extrusion process. Pellets and the chemical foaming agent (azodicarbonamide) were dry-mixed and foamed in an injection-molding machine. Densities and mechanical properties of the foamed biocomposites samples were measured and analyzed using central composite design (CCD). The results showed that both filler loading and coupling agent contents affected the density and mechanical properties of foamed biocomposites. Densities in the range of 0.57 to 0.81 gr cm-3 were achieved. Best results were obtained when less than 20% wheat straw flour and 1% coupling agent content were used. The flexural modulus and tensile modulus of foamed biocomposites were improved with increasing filler loading. However, flexural strength, tensile strength, elongation at break, and impact strength values were diminished. The tensile strength of the biocomposites was positively affected by CA contents, but other mechanical properties were not affected by it. Overall, injection molded foamed biocomposites with moderate mechanical properties were produced.