Enhanced sound insulation properties of microporous PMMA foams by constructing novel multilayered and directional cell structure (MDCS)

The main purpose of this study is to improve the performance of soundproofing materials through structure design without any functional phases. The sound insulation properties of PMMA microporous foams with multilayered and directional cell structure (MDCS) were investigated. The influence of the MDCS on sound transmission loss was discussed in detail. In addition, the mechanism for improving the sound transmission loss of the multilayered foams was discussed. The results show that the sound transmission loss value of the multilayered foams is up to 29.70 dB, which is 29.5% higher than that of the single-layer foams. It is due to the MDCS, which reduces the cell size of the foams, leading to increase the reflection and scattering of sound waves in pores. Meanwhile, the MDCS accompanied by multilayer interfaces increases the multiple reflection of sound waves at the interfaces. Besides, the smaller cell size and higher cell density strengthen the stiffness of the foams, which promotes the sound insulation properties. This study presents a novel and convenient method to design modern sound insulation materials.     

Influence of process parameters on mechanical properties of physically foamed,fiber reinforced polypropylene parts

Due to the high complexity of the foaming technology, the relationship between processing and final properties of parts produced is not completely understood. Investigating the causality chain Processing–Morphology–Properties is of great importance, especially for the automotive industry, in order to be able to tailor the mechanical properties of foamed parts. This article examines and qualifies the effects of seven process parameters (melt/mold temperature, degree of foaming, injection speed, delay time, gas content, and back pressure) on biaxial bending and flexural behavior—the predominant deformation mechanisms in interior automotive applications—of foamed plaques, using the MuCell process. The results clearly show that three major factors (mold temperature, degree of foaming, and delay time) have significant impact on the mechanical properties of the foamed parts. For a clear understanding of these interactions, computed tomography scans of certain plaques are correlated to process parameters and mechanical performance. This article should forge a bridge between production and performance. © 2018 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47275.     

Rheology,morphology, and mechanical properties of HMSPP/POE blends and its alternate layered foam

In this article, the multilayered foaming sheet with alternate layered structure was successfully prepared through multilayer co‐extrusion. The high melt strength polypropylene (HMSPP)/poly (ethylene‐co‐octene) (POE) blend and POE were designed as foaming layers and film layers, respectively. POE was added into HMSPP to reduce the crystalline degree and improve the processing performance. The rheological results indicated that the addition of POE had a little effect on relaxation process and the strain hardening behavior of HMSPP when the POE content was lower than 50%. The results of the foam morphology showed that the cell size and its distribution of the multilayered foaming sheet with alternate layers were better than that with single layer. In addition, the cell size reduced and the cell density increased with increasing the number of layers from 4 to 32. The mechanical properties of the multilayered foaming sheet with alternate layers also could be improved through assembling of foaming layers and film layers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41339.     

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

Epoxy 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.     

Facile fabrication of polyimide foam sheets with millimeter thickness: Processing,morphology, and properties

A series of polyimide foam sheets (PIFSs) with thickness of 0.5 mm using 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 3,4′‐oxydianiline (3,4′‐ODA), and polyaryl polymethylene isocyanate (PAPI) as main materials were first fabricated by liquid foaming and compression molding technology. The effects of different PAPI contents and 3,4′‐ODA contents on the structures and properties of PIFSs were investigated. The results indicated that PIFSs exhibited a structure that front surface displayed closed cells made of damaged cell walls and membranes, while internal cells were open, and elliptic vacancies were flatted in the thickness direction from the cross section. The average cellular diameter increased with increasing PAPI loading. In addition, the introduction of 3,4′‐ODA increased the average cell size of PIFSs. Further, PIFSs had density of 0.087–0.239 g/cm³, elongation at break of 3.75–8.01% and tensile toughness of 3.46 × 10^?2?13.87 × 10^?2 J/cm³. Notably, they exhibited higher tensile strength of 1.89–5.42 MPa and lower thermal conductivity of 14.727–19.25 mW/m ?K at 24°C, compared to the polyimide foams reported earlier. The sound absorption coefficients (α) of samples with different PAPI contents increased and then decreased with increasing PAPI content. At low frequencies, a certain content of 3,4′‐ ODA allowed an improvement of the acoustical behavior of PIFSs, and the α increased and then decreased with increasing density. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39881.     

Supermolecular morphology of polypropylene filled with nanosized silica

The supermolecular morphology of injection‐molded SiO₂/polypropylene (PP) nanocomposites was investigated via thin sections analyzed under polarized light and the systematic development of an appropriate etching technique, which allowed the study of the supermolecular morphologies with light microscopy (LM) and high‐resolution field emission scanning electron microscopy (FESEM). In parallel, information regarding the dispersion, distribution state, and morphology of SiO₂ particles was investigated via transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of the ion‐polished and fractured surfaces of SiO₂‐filled PP. The TEM/SEM results demonstrated an almost homogeneous dispersion and distribution of SiO₂ particle agglomerates in the PP matrix. With polarized transmitting LM, reflecting LM, and FESEM, the spherulitic structure of the nanocomposites could be visualized to obtain information on the nanoparticle influence on the crystallization and structural behavior. The size and size distribution of the spherulites analyzed with transmitting light (thin sections) and reflecting light (etched specimens) showed an excellent correlation. With increasing filler loading, the mean size of the spherulites decrease as did the degree of crystallinity. This was a clear indication that the particles acted as nucleation agents and, on the other hand, hindered the arrangement of the molecules during the crystallization. As a result, the particles were most likely located in three areas: the center of the spherulites, the areas between the highly crystalline branches, and the spherulite boundaries. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39655.     

Foaming of polypropylene with supercritical carbon dioxide: An experimental and theoretical study on a new process

A new process was used to foam polypropylene (PP) with batch foaming technique with supercritical carbon dioxide (scCO₂) as the blowing agent. Comparing with the conventional process, the new one takes less time to foam and the foaming temperature range is much broader, which is about 2.5 h and 55°C, respectively. An activation model was established on the basis of mass equilibrium, this model was combined with classical nucleation theory and S‐L EOS model to explain foaming behaviors of PP and simulate the cell nucleation and cell diameter. A satisfactory agreement between calculated and experimental values was obtained. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2877–2885, 2013     

Compressive and thermal characterization of syntactic foams containing hollow silicon carbide particles with porous shell

Silicon carbide hollow particle (SiC_HS) reinforced vinyl ester matrix syntactic foams are prepared and characterized for compressive properties and coefficient of thermal expansion (CTE). Two types of SiC_HS were utilized in 60 vol % to prepare syntactic foams. These SiC_HS had ratio of inner to outer radius of 0.91 and 0.84 for the thin and thick walled particles. The specific compressive strength values were 33.4 and 38.8 kPa/kg/m³ and the specific compressive modulus values were 0.8 MPa/kg/m³ and 0.6 MPa/kg/m³ for the thin and thick walled SiC_HS‐filled syntactic foams, respectively. The shell of the hollow particles contained microporous voids, and the porosity was estimated as 16.6% and 24.8% in the walls of the thin and thick walled particles, respectively. The shell porosity adversely affected the specific compressive strength and the modulus of the syntactic foam. However, the SiC_HS‐filled syntactic foams exhibited low CTE values (26.7 and 15.9 × 10^?6/°C). These CTE values were 65.1% and 79.3% lower than the CTE of the neat resin. Such properties can be useful for applications where syntactic foams are exposed to high temperatures and dimensional stability is important. A theoretical model is used to estimate the porosity level in the SiC shells and estimate the effective mechanical properties of the porous SiC material that forms the particle shell. Such analysis can help in using the models as predictive tools to estimate the mechanical properties of syntactic foams. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40689.     

Density reduction behaviors and cell morphology in extrusion of LLDPE/wood fiber composites with physical and chemical blowing agents

Foamed wood fiber/plastic composites (WPC) with a fine-cell structure offer many benefits compared with the unfoamed WPC, such as the reduced material cost and density, the improved toughness, and the enhanced processability. However, it is extremely challenging to achieve the desired density reduction and obtain a fine-cell structure simultaneously. One of the obstacles is that the volatiles released from the wood fiber (WF) during processing should be suppressed to ensure a fine-cell structure. Linear low-density polyethylene (LLDPE) has a relatively low melting temperature, and it can reduce the processing temperature and suppress volatiles when used as a polymer matrix for foamed WPC. This paper systematically investigates the foamability of LLDPE/WF composites in a continuous foam extrusion, with both a chemical blowing agent and a physical blowing agent (PBA). It turns out that the PBA-based foaming led to a smaller cell size and a narrower cell size distribution. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48829.     

Effect of crystalline structure on the cell morphology and mechanical properties of polypropylene foams fabricated by core-back foam injection molding

Foam injection molding (FIM) is an advanced technology for preparing lightweight plastic foams, but its inferior mechanical performance remains a challenge. In this study, microcellular injection-molded β-polypropylene (β-PP) foams with high ductility were successfully prepared by combing the β-nucleating agent with controllable temperature field. Foaming results showed that the microcellular β-PP foams exhibiting a cell size of about 8 μm and cell density over 10⁸ cells/cm³ were prepared with a crystalline diameter approximately 5 μm, while PP foams had a rather large cell size approximately 150 μm and low cell density of 10⁵ cells/cm³ with 30 μm crystalline size. As a result, this significant improvement in cell structure as well as the crystalline size lead to a significant increment of 86% for the ductility of β-PP foams. This work offers a facile strategy to prepare injection-molded foams with desirable mechanical properties for their wide range of applications, such as automotive construction and consumer electronics.     

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer (COC)—including CO₂ solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low T_g (78°C) and high T_g (158°C) were studied. Solubilities are 20–50% higher in high T_g COC than in the low T_g COC across the saturation temperature range. Diffusivities are about 15% higher on average in high T_g COC for temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low T_g COC due to it being in the rubbery state. Under similar gas concentration, high T_g COC starts foaming at a higher temperature. And the foam density decreases faster in low T_g COC with foaming temperature. Also, high T_g COC foams show about two orders of magnitude higher cell nucleation density than the low T_g COC foams. The effect of saturation temperature on microcellular foaming can be viewed as the effect of CO₂ concentration. Nucleation density increases and cell size decreases exponentially with increasing CO₂ concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high‐T_g COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low‐density high‐T_g COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42226.     

Graphene/polypropylene nanocomposites with improved thermal and mechanical properties

Small amount of large surface area graphene (G) is expected to significantly alter functional properties of polymers. The property enhancement is a function of degree of exfoliation and dispersion of G as well as its compatibility with base polymer. However, nonpolar nature of polyolefins such as polypropylene (PP) restricts homogeneous dispersion of G, leading to significant agglomeration and properties reduction. In this work, two compatibilizers, poly (ethylene-co-butyl acrylate) (EBA) (new compatibilizer) and PP-grafted-maleic anhydride (MA-PP) (conventional compatibilizer) were compared to enhance the dispersion efficacy of G in PP. The EBA-compatibilized nanocomposites exhibited 44% increase in the Young's modulus compared to 32% increment in MA-PP-compatibilized nanocomposites. Higher elongation at break for EBA-compatibilized nanocomposites is attributed to lower degree of crystallinity in these nanocomposites. On the other hand, EBA-compatibilized nanocomposites showed significantly improved thermal stability compared to MA-PP-compatibilized nanocomposites. The results indicate that EBA may act as a potential compatibilizer for G/PP nanocomposites.     

The influence of in situ synthesized nanoparticles on microstructure and compression properties of polymer foams during supercritical carbon dioxide foaming

The influence of in situ synthesized nanoparticles on the microstructure and compression properties of polymer foams during supercritical carbon dioxide foaming has been investigated. The in situ synthesized Ag nanoparticles were chosen to be heterogeneous nucleating agent. For achieving our target, the influence of the nanoparticle size on the cell structure and the nucleation mechanism has been detailed discussed firstly. The results show that the in situ synthesized nanoparticles can be heterogeneous nucleation agent to improve the cell density of the PMMA‐based foams. The particle size is able to reduce to the critical size of heterogeneous nucleation agent and, then, can highly improve the cell density of the foams. The Ag nanoparticles with average size of 2.2 nm led to 85% increase in compressive strength of the foams. The improvement of strength of the polymer matrix and the microstructure of the foams can lead to the remarkable increase in the mechanical properties of the foams. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44629.     

Mechanical and nonisothermal crystallization properties of coal gasification fine slag glass bead-filled polypropylene composites

Coal gasification fine slag (CGFS) was subjected to calcination at 600 °C for 7 h, forming CGFS glass beads (CGFSGB). CGFSGB was successfully incorporated into polypropylene (PP) by melt compounding. The results indicated that CGFSGB has the potential to replace calcium carbonate in the plastics market. Thermogravimetric analysis showed obvious reinforcement in thermal stability by incorporation of CGFSGB, but crystallization ability decreased. The CGFSGB was modified with 3-methacryloxypropyltrimethoxy silane (KH570) and hydrochloric acid (HCl) to improve the compatibility between the CGFSGB and PP, resulting in CGFSGB-S and CGFSGB-A, respectively. The tensile strength, thermal stability, and crystallization ability of PP composites and dispersity of the CGFSGB were increased after modification by KH570 and HCl, and the PP/CGFSGB-A composites showed better performance than PP/CGFSGB-S. Surface area and pore structure analysis and transmission electron microscopy revealed that good mechanical performance of PP/CGFSGB-A may be attributed to existence of mesopores in CGFSGB-A. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47803.     

Extrusion foaming behavior of a polypropylene/nanoclay microcellular foam

With maleic anhydride grafted polypropylene (PP‐g‐MAH) as a compatibilizer, composites of block‐copolymerized polypropylene (B‐PP)/nanoclay were prepared. The effects of the PP‐g‐MAH and nanoclay content on the crystallization and rheological properties of B‐PP were investigated. The microcellular foaming behavior of the B‐PP/nanoclay composite material was studied with a single‐screw extruder foaming system with supercritical (SC) carbon dioxide (CO₂) as the foaming agent. The experimental results show that the addition of nanoclay and PP‐g‐MAH decreased the melt strength and complex viscosity of B‐PP. When 3 wt % SC CO₂ was injected as the foaming agent for the extrusion foaming process, the introduction of nanoclay and PP‐g‐MAH significantly increased the expansion ratio of the obtained foamed samples as compared with that of the pure B‐PP matrix, lowered the die pressure, and increased the cell population density of the foamed samples to some extent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44094.     

Effects of butyl acrylate modified polypropylene on structural and thermal properties of foamed polypropylene

In this work, the melt strength of PP matrix was reinforced by crosslinking‐modified PP (CM‐PP) which was yielded by peroxide‐initiated crosslinking of linear PP with butyl acrylate (BA). The nano‐silica aerogel (nano‐SiO₂) worked as a nucleating agent for foaming. The effects of CM‐PP with the various contents of BA on the foaming behavior and thermal property of PP were studied by measurements of density, thermal conductivity, Vicat softening temperature and SEM. The results showed that the foamed PP got the best properties when the crosslinking PP modified with the weight ratio of butyl acrylate was 10 wt %. The density of the obtained foamed PP with uniform closed cells was as low as 0.23 g/cm³, the thermal conductivity was 0.044 W/(m K), and the Vicat softening temperature was 120 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44340.     

Mechanical properties and fracture morphology of Al(OH)3/polypropylene composites modified by PP grafting with acrylic acid

Al(OH)₃/polypropylene (PP) composites modified by polypropylene grafted with acrylic acid (FPP) were prepared by melt extrusion. Effect of PP grafting with acrylic acid on mechanical properties and fracture morphology of Al(OH)₃/polypropylene composites were investigated. Although incorporation of Al(OH)₃ reduced the mechanical properties of PP, addition of FPP increased the mechanical properties of Al(OH)₃/PP composites. It is suggested that addition of FPP improve the dispersion of Al(OH)₃ and the interfacial interaction between filler and matrix. Mechanical properties of Al(OH)₃/FPP/PP composites depend on the grafting rate and the content of FPP. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2617–2623, 2001     

Interfacial tuning and designer morphologies of microporous membranes based on polypropylene/natural rubber nanocomposites

Microporous polypropylene (PP) nanocomposite membranes are in great demand in various fields such as energy harvesting, water purification, and other industrial applications. Thin films of PP/natural rubber (NR) blend nanocomposite have been prepared by melt mixing and the membranes are made porous by extracting the NR phase from the blend. The present study gives a better insight into the nanoparticle shape and localization-tailored porous morphology of PP membrane. Thermodynamic prediction of nanofiller localization and its impact on morphology were studied. 2D clay platelets in PP matrix tune the morphology of the porous membrane into lamellar, whereas spherical nanofillers give elongated spherical pores. The localization of nanoparticles was observed using transmission electron microscope, which is also confirmed from theoretical prediction of localization of nanofillers with the help of interfacial energy and surface tension. Thermal studies reveal that nanofillers enhance the thermal stability of polymers. Mechanical studies reveal that nanoparticles improve the mechanical properties of the system. 2D platelet shaped-nanofillers enhance the mechanical strength of the polymer up to 39%, which is higher than that obtained for 3D spherical nanofillers. Nanofiller shape and localization have a great influence in deciding the properties and porosity of the membrane.