Polymers

2024

Jump to: 2023, 2022

13 pages, 4869 KiB

Open AccessArticle

Dispersion of Hydrophilic Nanoparticles in Natural Rubber with Phospholipids

by Jiramate Kitjanon, Nililla Nisoh, Saree Phongphanphanee, Nattaporn Chattham, Mikko Karttunen and Jirasak Wong-ekkabut

Polymers 2024, 16(20), 2901; https://doi.org/10.3390/polym16202901 - 15 Oct 2024

Viewed by 649

Abstract

Coarse-grained molecular dynamics (CGMD) simulations were employed to investigate the effects of phospholipids on the aggregation of hydrophilic, modified carbon-nanoparticle fillers in cis-polyisoprene (cis-PI) composites. The MARTINI force field was applied to model dipalmitoylphosphatidylcholine (DPPC) lipids and hydrophilic modified fullerenes [...] Read more.

Coarse-grained molecular dynamics (CGMD) simulations were employed to investigate the effects of phospholipids on the aggregation of hydrophilic, modified carbon-nanoparticle fillers in cis-polyisoprene (cis-PI) composites. The MARTINI force field was applied to model dipalmitoylphosphatidylcholine (DPPC) lipids and hydrophilic modified fullerenes (HMFs). The simulations of DPPC in cis-PI composites show that the DPPC lipids self-assemble to form a reverse micelle in a rubber matrix. Moreover, HMF molecules readily aggregate into a cluster, in agreement with the previous studies. Interestingly, the mixture of the DPPC and HMF in the rubber matrix shows a cluster of HMF is encapsulated inside the DPPC reverse micelle. The HMF encapsulated micelles disperse well in the rubber matrix, and their sizes are dependent on the lipid concentration. Mechanical and thermal properties of the composites were analyzed by calculating the diffusion coefficients (D), bulk modulus (κ), and glass transition temperatures (T_g). The results suggest that DPPC acts as a plasticizer and enhances the flexibility of the HMF-DPPC rubber composites. These findings provide valuable insights into the design and process of high-performance rubber composites, offering improved mechanical and thermal properties for various applications. Full article

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22 pages, 18654 KiB

Open AccessArticle

Optimization of Glass-Powder-Reinforced Recycled High-Density Polyethylene (rHDPE) Filament for Additive Manufacturing: Transforming Bottle Caps into Sound-Absorbing Material

by Sarah Iftin Atsani and Swee Leong Sing

Polymers 2024, 16(16), 2324; https://doi.org/10.3390/polym16162324 - 16 Aug 2024

Cited by 1 | Viewed by 1143

Abstract

Additive manufacturing presents promising potential as a sustainable processing technology, notably through integrating post-consumer recycled polymers into production. This study investigated the recycling of high-density polyethylene (rHDPE) into 3D printing filament, achieved by the following optimal extrusion parameters: 180 °C temperature, 7 rpm [...] Read more.

Additive manufacturing presents promising potential as a sustainable processing technology, notably through integrating post-consumer recycled polymers into production. This study investigated the recycling of high-density polyethylene (rHDPE) into 3D printing filament, achieved by the following optimal extrusion parameters: 180 °C temperature, 7 rpm speed, and 10% glass powder addition. The properties of the developed rHDPE filament were compared with those of commonly used FDM filaments such as acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) to benchmark the performance of rHDPE against well-established materials in the 3D printing industry, providing a practical perspective for potential users. The resulting filament boasted an average tensile strength of 25.52 MPa, slightly exceeding ABS (25.41 MPa) and comparable to PLA (28.55 MPa). Despite diameter fluctuations, the filament proved usable in 3D printing. Mechanical tests compared the rHPDE filament 3D printed objects with ABS and PLA, showing lower strength but exceptional ductility and flexibility, along with superior sound absorption. A life cycle analysis underscored the sustainability advantages of rHDPE, reducing environmental impact compared to conventional disposal methods. While rHDPE falls behind in mechanical strength against virgin filaments, its unique attributes and sustainability position it as a valuable option for 3D printing, showcasing recycled materials’ potential in sustainable innovation. Full article

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13 pages, 6975 KiB

Open AccessArticle

Frequency-Dependent Fatigue Properties of Additively Manufactured PLA

by Martin Česnik and Janko Slavič

Polymers 2024, 16(15), 2147; https://doi.org/10.3390/polym16152147 - 29 Jul 2024

Viewed by 796

Abstract

Vibration-fatigue failure occurs when a structure is dynamically excited within its natural frequency range. Unlike metals, which have constant fatigue parameters, polymers can exhibit frequency-dependent fatigue parameters, significantly affecting the vibration resilience of 3D-printed polymer structures. This manuscript presents a study utilizing a [...] Read more.

Vibration-fatigue failure occurs when a structure is dynamically excited within its natural frequency range. Unlike metals, which have constant fatigue parameters, polymers can exhibit frequency-dependent fatigue parameters, significantly affecting the vibration resilience of 3D-printed polymer structures. This manuscript presents a study utilizing a novel vibration-fatigue testing methodology to characterize the frequency dependence of polymer material fatigue parameters under constant temperature conditions. In this investigation, 3D-printed PLA samples with frequency-tunable geometry were experimentally tested on an electro-dynamical shaker with a random vibration profile. Using the validated numerical models, the estimation of vibration-fatigue life was obtained and compared to the experimental results. Performing the numerical minimization of estimated and actual fatigue lives, the frequency-dependent fatigue parameters were assessed. In particular, the results indicate that the tested samples exhibit varying fatigue parameters within the loading frequency range of 250–750 Hz. Specifically, as the loading frequency increases, the fatigue exponent increases and fatigue strength decreases. These findings confirm the frequency dependence of fatigue parameters for 3D-printed polymer structures, underscoring the necessity of experimental characterization to reliably estimate the vibration-fatigue life of 3D-printed polymer structures. The utilization of the introduced approach therefore enhances the vibration resilience of the 3D-printed polymer mechanical component. Full article

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20 pages, 5525 KiB

Open AccessArticle

Image Data-Centric Visual Feature Selection on Roll-to-Roll Slot-Die Coating Systems for Edge Wave Coating Defect Detection

by Yoonjae Lee, Junyoung Yun, Sangbin Lee and Changwoo Lee

Polymers 2024, 16(8), 1156; https://doi.org/10.3390/polym16081156 - 19 Apr 2024

Viewed by 1154

Abstract

Roll-to-roll (R2R) manufacturing depends on a system’s capability to deposit high-quality coatings with precise thickness, width, and uniformity. Therefore, consistent maintenance requires the immediate and accurate detection of coating defects. This study proposes a primary color selection (PCS) method to detect edge defects [...] Read more.

Roll-to-roll (R2R) manufacturing depends on a system’s capability to deposit high-quality coatings with precise thickness, width, and uniformity. Therefore, consistent maintenance requires the immediate and accurate detection of coating defects. This study proposes a primary color selection (PCS) method to detect edge defects in R2R systems. This method addresses challenges associated with training data demands, complexity, and defect adaptability through a vision data-centric approach, ensuring precise edge coating defect detection. Using color information, high accuracy was achieved while minimizing data capacity requirements and processing time. Precise edge detection was facilitated by accurately distinguishing coated and noncoated regions by selecting the primary color channel based on color variability. The PCS method achieved superior accuracy (95.8%), outperforming the traditional weighted sum method (78.3%). This method is suitable for real-time detection in manufacturing systems and mitigates edge coating defects, thus facilitating quality control and production optimization. Full article

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20 pages, 19013 KiB

Open AccessArticle

Control of Meniscus Formation Using an Electrohydrodynamics Module in Roll-to-Roll Systems for the Stable Coating of Functional Layers

by Minjae Kim, Minho Jo, Jaehyun Noh, Sangbin Lee, Junyoung Yun, Gyoujin Cho and Changwoo Lee

Polymers 2024, 16(6), 845; https://doi.org/10.3390/polym16060845 - 19 Mar 2024

Viewed by 1919

Abstract

In fabricating functional layers, including thin-film transistors and conductive electrodes, using roll-to-roll (R2R) processing on polymer-based PET film, the instability of the slot-die coating meniscus under a high-speed web impedes functional layer formation with the desired thickness and width. The thickness profiles of [...] Read more.

In fabricating functional layers, including thin-film transistors and conductive electrodes, using roll-to-roll (R2R) processing on polymer-based PET film, the instability of the slot-die coating meniscus under a high-speed web impedes functional layer formation with the desired thickness and width. The thickness profiles of the functional layers significantly impact the performance of the final products. In this study, we introduce an electrohydrodynamic (EHD)-based voltage application module to a slot-die coater to ensure the uniformity of the cross-machine direction (CMD) thickness profile within the functional layer and enable a stable, high-speed R2R process. The module can effectively control the spreadability of the meniscus by utilizing variations in the surface tension of the ink. The effectiveness of the EHD module was experimentally verified by applying a high voltage to a slot-die coater while keeping other process variables constant. As the applied voltage increases, the CMD thickness deviation reduces by 64.5%, and the production rate significantly increases (up to 300%), owing to the formation of a stable coated layer. The introduction of the EHD-based application module to the slot-die coater effectively controlled the spreadability of the meniscus, producing large-area functional layers. Full article

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2023

Jump to: 2024, 2022

17 pages, 4415 KiB

Open AccessArticle

European Database of Explanted UHMWPE Liners from Total Joint Replacements: Correlations among Polymer Modifications, Structure, Oxidation, Mechanical Properties and Lifetime In Vivo

by Miroslav Slouf, Veronika Gajdosova, Jiri Dybal, Roman Sticha, Petr Fulin, David Pokorny, Jesús Mateo, Juan José Panisello, Vicente Canales, Francisco Medel, Alessandro Bistolfi and Pierangiola Bracco

Polymers 2023, 15(3), 568; https://doi.org/10.3390/polym15030568 - 21 Jan 2023

Cited by 8 | Viewed by 1977

Abstract

This contribution lays the foundation for the European database of explanted UHMWPE liners from total joint replacements. Three EU countries (Czech Republic, Italy and Spain) have joined their datasets containing anonymized patient data (such as age and BMI), manufacturer data (such as information [...] Read more.

This contribution lays the foundation for the European database of explanted UHMWPE liners from total joint replacements. Three EU countries (Czech Republic, Italy and Spain) have joined their datasets containing anonymized patient data (such as age and BMI), manufacturer data (such as information on UHMWPE crosslinking, thermal treatment and sterilization), orthopedic evaluation (such as total duration of the implant in vivo and reasons for its revision) and material characterization (such as oxidative degradation and micromechanical properties). The joined database contains more than 500 entries, exhibiting gradual growth, and it is beginning to show interesting trends, which are discussed in our contribution, including (i) strong correlations between UHMWPE oxidative degradation, degree of crystallinity and microhardness; (ii) statistically significant differences between UHMWPE liners with different types of sterilization; (iii) realistic correlations between the extent of oxidative degradation and the observed reasons for total joint replacement failures. Our final objective and task for the future is to continuously expand the database, involving researchers from other European countries, in order to create a robust tool that will contribute to the better understanding of structure–properties–performance relationships in the field of arthroplasty implants. Full article

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20 pages, 5263 KiB

Open AccessArticle

Impact of Zinc Oxide Addition on Oil Palm Empty Fruit Bunches Foamed Polymer Composites for Automotive Interior Parts

by Taufan Arif Adlie, Nurdin Ali, Syifaul Huzni, Ikramullah Ikramullah and Samsul Rizal

Polymers 2023, 15(2), 422; https://doi.org/10.3390/polym15020422 - 13 Jan 2023

Cited by 9 | Viewed by 2026

Abstract

The sustainable use of agricultural waste to generate valuable products while minimizing environmental burdens is increasing rapidly. Multiple sources of fibers have been intensively studied concerning their application in various fields and industries. However, few publications have extensively discussed the property’s performance of [...] Read more.

The sustainable use of agricultural waste to generate valuable products while minimizing environmental burdens is increasing rapidly. Multiple sources of fibers have been intensively studied concerning their application in various fields and industries. However, few publications have extensively discussed the property’s performance of oil palm empty fruit bunches (OPEFB) composites. With main properties similar to composites currently listed for industrial applications, OPEFB is worth listing as a potential composite for industrial applications and non-structural material alternatives. OPEFB-reinforced polymer composites are expected to be applied to automotive interior parts. This study aims to determine the effect of adding zinc oxide (ZnO) and polyurethane on OPEFB-reinforced polymer composites for automotive interior parts. This composite was produced using the hand lay-up method with 70% resin, 15% OPEFB fiber, 15% polyurethane as a blowing agent, and four variations of ZnO at 5%, 10%, 15%, and 20%. The OPEFB particle sizes are 40, 60, 80, and 100, respectively. The composite was examined to determine mechanical, morphology, chemical, and thermal characteristics. It was observed that the addition of 20% ZnO caused ZnO agglomeration, weakening the interfacial bond between OPEFB particles, polyester, polyurethane, and ZnO filler. Overall, the results showed that adding ZnO and polyurethane to the composite increased tensile, compressive, flexural, and impact strength, as well as thermal stability with more significant values up to 160%, 225%, 100%, 100%, and 4.3%, respectively. This result depicted that the best composition was specimens with 15% ZnO and 149 microns OPEFB fibers particle size. It is considered a promising candidate to be applied in automotive interior components. Full article

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14 pages, 3735 KiB

Open AccessArticle

Effect of the Addition of Different Natural Waxes on the Mechanical and Rheological Behavior of PLA—A Comparative Study

by Mónica Elvira Mendoza-Duarte, Iván Alziri Estrada-Moreno, Erika Ivonne López-Martínez and Alejandro Vega-Rios

Polymers 2023, 15(2), 305; https://doi.org/10.3390/polym15020305 - 6 Jan 2023

Cited by 10 | Viewed by 7746

Abstract

In this study, poly(lactic acid) (PLA) blended with different natural waxes (beeswax, candelilla, carnauba, and cocoa) was investigated. Different wax amounts, 3, 5, 10, and 15 wt%, were incorporated into the PLA using a Brabender internal mixer. The blends were characterized by thermogravimetric [...] Read more.

In this study, poly(lactic acid) (PLA) blended with different natural waxes (beeswax, candelilla, carnauba, and cocoa) was investigated. Different wax amounts, 3, 5, 10, and 15 wt%, were incorporated into the PLA using a Brabender internal mixer. The blends were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), rotational rheometer (RR), dynamic mechanical analysis (DMA), and contact angle to observe the effect of the different waxes on the PLA physicochemical, rheological, mechanical behavior, and wetting properties. The complex viscosity of the blends was studied by employing a RR. The effect of the addition of the waxes on the mechanical properties of PLA was evaluated by DMA in the tension modality. A slight decrease in the thermal stability of PLA was observed with the addition of the waxes. However, in the case of the mechanical properties, the cocoa wax showed a considerable effect, especially in the elongation at break of PLA. Likewise, waxes had an essential impact on the water affinity of PLA. Specifically, with the addition of cocoa, the PLA became more hydrophilic, while the rest of the waxes increased the hydrophobic character. Full article

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2022

Jump to: 2024, 2023

15 pages, 2011 KiB

Open AccessArticle

Effect of High-Pressure Treatments on the Properties of Food Packaging Materials with or without Antimicrobials

by Belén Soriano Cuadrado, Antonio Peñas Sanjuan, Javier Rodríguez López, Irene Delgado Blanca, Maria José Grande, Rosario Lucas, Antonio Galvez and Rubén Pérez Pulido

Polymers 2022, 14(24), 5535; https://doi.org/10.3390/polym14245535 - 17 Dec 2022

Viewed by 1861

Abstract

The aim of this research work was the comparative study of the different properties of interest in the case of plastic materials for food use before and after being subjected to treatment by high hydrostatic pressure (HHP) as well as the impact of [...] Read more.

The aim of this research work was the comparative study of the different properties of interest in the case of plastic materials for food use before and after being subjected to treatment by high hydrostatic pressure (HHP) as well as the impact of additivation with antimicrobials. This method of food preservation is currently on the rise and is of great interest because it is possible to extend the shelf life of many foods without the need for the use of additives or thermal processing, as is the case with other preservation methods currently used. The effects of HHP treatment (680 MPa for 8 min) on plastic materials commonly used in the food industry were studied. These materials, in sheet or film form, were polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), multilayer polyethylene terephthalate–ethylene-vinyl alcohol copolymer–polyethylene (PET–EVOH–PE), multilayer polyethylene–polyethylene terephthalate (PE–PET), polyvinyl chloride aluminum (PVC–AL), and polylactic acid (PLA), which were provided by manufacturing companies in the sector. PE, PP, and PLA activated with tyrosol, zinc oxide, or zinc acetate were also tested. The phenomena and properties, such as overall migration, thermal behavior, oxygen barrier, and physical properties were analyzed before and after the process. The results show that the HHP process only slightly affected the properties of the materials. After pressurization, oxygen permeability increased greatly in PVC–AL (from 7.69 to 51.90) and decreased in PLA (from 8.77 to 3.60). The additivation of the materials caused a change in color and an increase in oxygen permeability. The additivated PE and PP showed migration values above the legal limit for certain simulants. The HHP treatment did not greatly affect the mechanical properties of the additivated materials. The main increases in the migration after HHP treatment were observed for PE activated with tyrosol or zinc oxide and for PS activated with zinc oxide. Activated PLA performed the best in the migration studies, irrespective of the HHP treatment. The results suggest that activated PLA could be used in HHP food processing as an inner antimicrobial layer in contact with the food packed in a container with the desired oxygen permeability barrier. Full article

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13 pages, 5131 KiB

Open AccessArticle

The Effect of the Addition of Copper Particles in High-Density Recycled Polyethylene Matrices by Extrusion

by Camila Arcos, Lisa Muñoz, Deborah Cordova, Hugo Muñoz, Mariana Walter, Manuel I. Azócar, Ángel Leiva, Mamié Sancy and Gonzalo Rodríguez-Grau

Polymers 2022, 14(23), 5220; https://doi.org/10.3390/polym14235220 - 30 Nov 2022

Cited by 3 | Viewed by 2370

Abstract

In this study, the effect of the recycling process and copper particle incorporation on virgin and recycled pellet HDPE were investigated by thermo-chemical analysis, mechanical characterization, and antibacterial analysis. Copper particles were added to pellet HDPE, virgin and recycled, using a tabletop single [...] Read more.

In this study, the effect of the recycling process and copper particle incorporation on virgin and recycled pellet HDPE were investigated by thermo-chemical analysis, mechanical characterization, and antibacterial analysis. Copper particles were added to pellet HDPE, virgin and recycled, using a tabletop single screw extruder. Some copper particles, called copper nano-particles (Cu-NPs), had a spherical morphology and an average particle size near 20 nm. The others had a cubic morphology and an average particle size close to 300 nm, labeled copper nano-cubes (Cu-NCs). The thermo-chemical analysis revealed that the degree of crystallization was not influenced by the recycling process: 55.38 % for virgin HDPE and 56.01% for recycled HDPE. The degree of crystallization decreased with the addition of the copper particles. Possibly due to a modification in the structure, packaging organization, and crystalline ordering, the recycled HDPE reached a degree of crystallization close to 44.78% with 0.5 wt.% copper nano-particles and close to 36.57% for the recycled HDPE modified with 0.7 wt.% Cu-NCs. Tensile tests revealed a slight reduction in the tensile strength related to the recycling process, being close to 26 MPa for the virgin HDPE and 15.99 MPa for the recycled HDPE, which was improved by adding copper particles, which were near 25.39 MPa for 0.7 wt.% copper nano-cubes. Antibacterial analysis showed a reduction in the viability of E. coli in virgin HDPE samples, which was close to 8% for HDPE containing copper nano-particles and lower than 2% for HDPE having copper nano-cubes. In contrast, the recycled HDPE revealed viability close to 95% for HDPE with copper nano-particles and nearly 50% for HDPE with copper nano-cubes. The viability of S. aureus for HDPE was lower than containing copper nano-particles and copper nano-cubes, which increased dramatically close to 80% for recycled HDPE with copper nano-particles 80% and 75% with copper nano-cubes. Full article

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17 pages, 5847 KiB

Open AccessArticle

A Node Detection Method Based on Johnson–Cook and Thin-Film IMD Characteristic Model Armor Damage Detection Repair and Subsequent Optimization

by Hanjui Chang, Guangyi Zhang, Yue Sun and Shuzhou Lu

Polymers 2022, 14(21), 4540; https://doi.org/10.3390/polym14214540 - 26 Oct 2022

Cited by 1 | Viewed by 1757

Abstract

In this paper, a node detection method is proposed for the detection of battle damage to armor. This experiment uses the special nature of the film to virtualize the surface of the armor IMD film coverage. The die index is a large area [...] Read more.

In this paper, a node detection method is proposed for the detection of battle damage to armor. This experiment uses the special nature of the film to virtualize the surface of the armor IMD film coverage. The die index is a large area and is easy to damage, but with the use of a unique IMD film stamping die, the possibility of damage decreases, which provides a damage prediction function for the armor. In addition, for the damaged armor, the same method can be used to detect because the damaged part more easily causes the surface film to rupture after being impacted, so it is possible to optimize the design of the armor and the molding through the die index. The die index can also detect the degree of damage to the damaged part of the damaged armor. Therefore, the IMD die index is introduced to quantify the data, and the degree of damage is judged by the IMD die index. The novelty of this work is that each node can efficiently detect the vulnerable damage position of the armor using the die index and then pass through the COMSOL. The Johnson–Cook stress model simulates the battle loss, obtains the stress deformation that occurs after the battle loss, and verifies the experiment by comparing the results obtained. Finally, the repair method is used to repair all the predicted battle damage parts based on additive manufacturing to ensure that they can be used again after repair. Full article

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13 pages, 4201 KiB

Open AccessArticle

Crystallization Behavior of Poly(ε-Caprolactone)-Hollow Glass Microspheres Composites for Rotational Molding Technology

by Adriano Vignali, Roberto Utzeri, Maurizio Canetti and Fabio Bertini

Polymers 2022, 14(20), 4326; https://doi.org/10.3390/polym14204326 - 14 Oct 2022

Viewed by 1755

Abstract

Composites suitable for rotational molding technology based on poly(ε-caprolactone) (PCL) and filled with hollow glass microspheres (HGM) or functionalized hollow glass microspheres (HGMf) were prepared via melt-compounding. The functionalization of glass microspheres was carried out by a silanization treatment in order to improve [...] Read more.

Composites suitable for rotational molding technology based on poly(ε-caprolactone) (PCL) and filled with hollow glass microspheres (HGM) or functionalized hollow glass microspheres (HGMf) were prepared via melt-compounding. The functionalization of glass microspheres was carried out by a silanization treatment in order to improve the compatibility between the inorganic particles and the polymer matrix and achieve a good dispersion of glass microspheres in the matrix and an enhanced filler–polymer adhesion. The crystallization behavior of materials was studied by DSC under isothermal and non-isothermal conditions and the nucleating effect of the glass microspheres was proven. In particular, the presence of silanized glass microspheres promoted faster crystallization rates and higher nucleation activity, which are enhanced by 75% and 50%, respectively, comparing neat PCL and the composite filled with 20 wt% HGMf. The crystalline and supermolecular structure of PCL and composites crystallized from the melt was evaluated by WAXD and SAXS, highlighting differences in terms of crystallinity index and structural parameters as a function of the adopted crystallization conditions. Full article

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20 pages, 4001 KiB

Open AccessArticle

Polycarbonate/Titania Composites Incorporating TiO₂ with Different Nanoscale Morphologies for Enhanced Environmental Stress Cracking Resistance in Dioctyl Phthalate

by Yasir Khalid, Amine Achour, Muhammad Aftab Akram and Mohammad Islam

Polymers 2022, 14(17), 3693; https://doi.org/10.3390/polym14173693 - 5 Sep 2022

Cited by 5 | Viewed by 2322

Abstract

Polycarbonate (PC) is susceptible to environmental stress cracking (ESC) when the conditions of pre-strain and presence of fluid with a compatible solubility index are both prevalent. One approach to counter this involves using nanoscale fillers to bridge the propagating microcracks, thus, effectively inhibiting [...] Read more.

Polycarbonate (PC) is susceptible to environmental stress cracking (ESC) when the conditions of pre-strain and presence of fluid with a compatible solubility index are both prevalent. One approach to counter this involves using nanoscale fillers to bridge the propagating microcracks, thus, effectively inhibiting impending failure. In this work, we report incorporation of titania (TiO₂) with different nanoscale morphologies into polycarbonate matrix to assess its effect on ESC resistance against dioctyl phthalate (DOP). Using a hydrothermal process with a NaOH/Ti molar ratio of 72, TiO₂ nanostructures were produced containing nanosheets with large surface area and nanotubes having typical diameter and length values of 15–20 nm and a few hundred nanometers, respectively. PC/TiO₂ composites were fabricated with up to 0.5 weight percent of TiO₂ nanoparticles (NPs), nanowires (NWs), or hybrid nanostructures (HNs). ESC tests were conducted by exposing test coupons to DOP oil at different temperatures and pre-strain conditions. The results showed that, under identical test conditions, while as-received PC grade exhibited complete fracture in ~3.1 h, PC/TiO₂-0.05HN composite took ~70 h to fail via surface cracking. SEM examination of the fracture surface revealed that homogeneous dispersion and efficient load-bearing capability of TiO₂ nanotubes and nanosheets impeded localized crack propagation by bridging the gap between the PC matrix segments. Liquid nitrogen fracture of the PC/TiO₂ composite further confirmed the critical role of TiO₂ hybrid nanostructures towards improvement in ESC resistance of PC matrix composites. Full article

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17 pages, 7742 KiB

Open AccessArticle

Mechanical Properties of Polypropylene-Based Flame Retardant Composites by Surface Modification of Flame Retardants

by Jinwoo Lee, Jae Hyung Park, Seung Bo Shim and Ji Eun Lee

Polymers 2022, 14(17), 3524; https://doi.org/10.3390/polym14173524 - 27 Aug 2022

Cited by 13 | Viewed by 3503

Abstract

A flame retardant refers to a substance that can be added to a material having the property of being efficiently combusted to improve the material physically and chemically. It should not affect the physical properties required for the final product. Halogen-based compounds are [...] Read more.

A flame retardant refers to a substance that can be added to a material having the property of being efficiently combusted to improve the material physically and chemically. It should not affect the physical properties required for the final product. Halogen-based compounds are representative flame retardants with excellent flame retardancy. However, their use is limited due to restrictions on the use of chemicals introduced due to human safety. Magnesium hydroxide, one alternative material of halogen flame retardants, is widely used as an eco-friendly flame retardant. However, the most significant disadvantage is high load. To find a solution to this problem, many studies have been conducted by mixing magnesium hydroxide with other additives to create a synergistic effect. In this study, flame retardancy and mechanical properties of polypropylene-based flame retardant composites as a function of mixing surface-modified magnesium hydroxide with phosphorus-based flame retardants were investigated. All materials including PP, additives, and flame retardants were mixed using an extrusion process. Specimens were prepared by an injection process of the compound made after mixing. As a result of the evaluation of the mechanical properties by the modified flame retardant, the relational expression of the mechanical performance degradation as a function of the amount of addition was obtained, and the tensile (CBATS) and bending strength (CBABS) were performed on the amount of flame retardant added. The relational expression obtained in this study is considered to be a formula for predicting the strength reduction according to the addition amount of the modified flame retardant and can be used in industry. In addition, it was found that the addition amount of the modified flame retardant had a greater effect on the lowering of the bending strength. Full article

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19 pages, 10652 KiB

Open AccessArticle

Study on the Effect of Processing Parameters on Residual Stresses of Injection Molded Micro-Pillar Array

by Xiaoyu Zhang, Tao Ding, Wanlin Wang, Jiezhen Liu and Can Weng

Polymers 2022, 14(16), 3358; https://doi.org/10.3390/polym14163358 - 17 Aug 2022

Cited by 7 | Viewed by 2102

Abstract

As one of the main methods for fabricating microstructured surfaces, micro-injection molding has the advantages of short cycle time, high production efficiency, and the potential for batch manufacturing. However, non-negligible residual stresses inside the molded part could affect the replication quality, dimensions, and [...] Read more.

As one of the main methods for fabricating microstructured surfaces, micro-injection molding has the advantages of short cycle time, high production efficiency, and the potential for batch manufacturing. However, non-negligible residual stresses inside the molded part could affect the replication quality, dimensions, and physical properties of the microstructure. Therefore, studying the effects of processing parameters on residual stresses is a necessary prerequisite to ensure the successful fabrication of microstructured parts. In this paper, an injection molding simulation model of micro-pillar arrays was developed using molecular dynamics software, and a series of injection molding experiments were conducted. It was found that increasing the mold temperature and melt temperature can reduce the thermal residual stresses and molecular orientation stresses, and effectively improve the uniformity of residual stress distribution. The increase in the packing pressure can make the shear field of flow more intense and increase the molecular orientation stresses, thus making the residual stresses more severe. Full article

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