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Injection Molding of Polymers and Polymer Composites

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: closed (25 February 2024) | Viewed by 20299

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Prof. Dr. Andrew N. Hrymak

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Department of Chemical and Biochemical Engineering, The University of Western Ontario, London, ON N6A, Canada
Interests: polymer processing; flow simulation; multi-phase system; polymer composites

Dr. Shengtai Zhou

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Guest Editor

Polymer Research Institute, The State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610017, China
Interests: materials engineering; polymer processing; foams
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Dear Colleagues,

The injection molding of polymers and polymer composites is a versatile way to fabricate multifunctional components or structural parts for applications in the fields of automotives, biomedicine, electronics, packaging, aerospace, etc. Processing methods of interest include conventional injection molding, foam injection molding, reaction injection molding, ultrasonic-assisted injection molding, and microinjection molding, as developed to suit the needs of the above-mentioned sectors. The properties of the molded parts are primarily determined by the development of crystalline structures, the distribution and orientation of functional fillers, which can be affected by the types of fillers and host matrices, part geometries, and processing conditions. This Special Issue provides a forum for the discussion of the injection molding of polymers and polymer composites, with a focus on state-of-the-art progress, developments, and new trends. Perspectives, review articles, full papers, short communications, and technical papers on this topic are welcome.

Prof. Dr. Andrew N. Hrymak
Dr. Shengtai Zhou
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

injection molding
crystalline properties
mechancial properties
electrical properties
thermal properties
microstructure

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Published Papers (11 papers)

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Editorial

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4 pages, 141 KiB

Open AccessEditorial

Injection Molding of Polymers and Polymer Composites

by Shengtai Zhou and Andrew N. Hrymak

Polymers 2024, 16(13), 1796; https://doi.org/10.3390/polym16131796 - 25 Jun 2024

Cited by 1 | Viewed by 1533

Abstract

Injection molding technology has been widely adopted to fabricate multifunctional polymeric components or structural parts for applications in fields such as automotives, electronics, packaging, aerospace, and many others [...] Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

Research

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13 pages, 7537 KiB

Open AccessArticle

Influence of Strong Shear Field on Structure and Performance of HDPE/PA6 In Situ Microfibril Composites

by Junwen Zhang, Yiwei Zhang, Yanjiang Li, Mengna Luo and Jie Zhang

Polymers 2024, 16(8), 1032; https://doi.org/10.3390/polym16081032 - 10 Apr 2024

Viewed by 1059

Abstract

As one of the most widely applied general-purpose plastics, high-density polyethylene (HDPE) exhibits good comprehensive performance. However, mechanical strength limits its wider application. In this work, we introduced the engineering plastic PA6 as a dispersed phase to modify the HDPE matrix and applied multiple shears generated by vibration to the polymer melt during the packing stage of injection molding. SEM, 2D-WXRD and 2D-SAXS were used to characterize the morphology and structure of the samples. The results show that under the effect of a strong shear field, the dispersed phase in the composites can form in situ microfibers and numerous high-strength shish-kebab and hybrid shish-kebab structures are formed. Additionally, the distribution of fibers and high-strength oriented structures in the composites expands to the core region with the increase in vibration times. As a result, the tensile strength, tensile modulus and surface hardness of VIM-6 can reach a high level of 66.5 MPa, 981.4 MPa and 72, respectively. Therefore, a high-performance HDPE product is successfully prepared in this study, which is of great importance for expanding the application range of HDPE products. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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21 pages, 17411 KiB

Open AccessArticle

The Modification of Useful Injection-Molded Parts’ Properties Induced Using High-Energy Radiation

by Martin Bednarik, Vladimir Pata, Martin Ovsik, Ales Mizera, Jakub Husar, Miroslav Manas, Jan Hanzlik and Michaela Karhankova

Polymers 2024, 16(4), 450; https://doi.org/10.3390/polym16040450 - 6 Feb 2024

Cited by 2 | Viewed by 1230

Abstract

The modification of polymer materials’ useful properties can be applicable in many industrial areas due to the ability to make commodity and technical plastics (plastics that offer many benefits, such as processability, by injection molding) useful in more demanding applications. In the case of injection-molded parts, one of the most suitable methods for modification appears to be high-energy irradiation, which is currently used primarily for the modification of mechanical and thermal properties. However, well-chosen doses can effectively modify the properties of the surface layer as well. The purpose of this study is to provide a complex description of high-energy radiation’s (β radiation) influence on the useful properties of injection-molded parts made from common polymers. The results indicate that β radiation initiates the cross-linking process in material and leads to improved mechanical properties. Besides the cross-linking process, the material also experiences oxidation, which influences the properties of the surface layer. Based on the measured results, the main outputs of this study are appropriately designed regression models that determine the optimal dose of radiation. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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19 pages, 8294 KiB

Open AccessArticle

Enhancing Amplification in Compliant Mechanisms: Optimization of Plastic Types and Injection Conditions

by Pham Son Minh, Van-Thuc Nguyen, Tran Minh The Uyen, Vu Quang Huy, Hai Nguyen Le Dang and Van Thanh Tien Nguyen

Polymers 2024, 16(3), 394; https://doi.org/10.3390/polym16030394 - 31 Jan 2024

Viewed by 1268

Abstract

This study surveys the impacts of injection parameters on the deformation rate of the injected flexure hinge made from ABS, PP, and HDPE. The flexure hinges are generated with different filling time, filling pressure, filling speed, packing time, packing pressure, cooling time, and melt temperature. The amplification ratio of the samples between different injection parameters and different plastic types is measured and compared to figure out the optimal one with a high amplification ratio. The results show that the relationship between the input and output data of the ABS, PP, and HDPE flexure hinges at different injection molding parameters is a linear relation. Changing the material or many injection molding parameters of the hinge could lead to a great impact on the hinge’s performance. However, changing each parameter does not lead to a sudden change in the input and output values. Each plastic material has different optimal injection parameters and displacement behaviors. With the ABS flexure hinge, the filling pressure case has the greatest amplification ratio of 8.81, while the filling speed case has the lowest value of 4.81. With the optimal injection parameter and the input value of 105 µm, the ABS flexure hinge could create a maximum average output value of 736.6 µm. With the PP flexure hinge, the melt temperature case achieves the greatest amplification ratio of 6.73, while the filling speed case has the lowest value of 4.1. With the optimal injection parameter and the input value of 128 µm, the PP flexure hinge could create a maximum average output value of 964.8 µm. The average amplification ratio values of all injection molding parameters are 6.85, 5.41, and 4.01, corresponding to ABS, PP, and HDPE flexure hinges. Generally, the ABS flexure hinge has the highest amplification ratios, followed by the PP flexure hinge. The HDPE flexure hinge has the lowest amplification ratios among these plastic types. With the optimal injection parameter and the input value of 218 µm, the HDPE flexure hinge could create a maximum average output value of 699.8 µm. The results provide more insight into plastic flexure hinges and broaden their applications by finding the optimal injection parameters and plastic types. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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15 pages, 4160 KiB

Open AccessArticle

Flexible Polyolefin Elastomer/Paraffin Wax/Alumina/Graphene Nanoplatelets Phase Change Materials with Enhanced Thermal Conductivity and Mechanical Performance for Solar Conversion and Thermal Energy Storage Applications

by Jie Tian, Chouxuan Wang, Kaiyuan Wang, Rong Xue, Xinyue Liu and Qi Yang

Polymers 2024, 16(3), 362; https://doi.org/10.3390/polym16030362 - 29 Jan 2024

Cited by 4 | Viewed by 1586

Abstract

In this study, electrically insulating polyolefin elastomer (POE)-based phase change materials (PCMs) comprising alumina (Al₂O₃) and graphene nanoplatelets (GNPs) are prepared using a conventional injection moulding technique, which exhibits promising applications for solar energy storage due to the reduced interfacial thermal resistance, excellent stability, and proficient photo-thermal conversion efficiency. A synergistic interplay between Al₂O₃ and GNPs is observed, which facilitates the establishment of thermally conductive pathways within the POE/paraffin wax (POE/PW) matrix. The in-plane thermal conductivity of POE/PW/GNPs 5 wt%/Al₂O₃ 40 wt% composite reaches as high as 1.82 W m⁻¹K⁻¹, marking a remarkable increase of ≈269.5% when compared with that of its unfilled POE/PW counterpart. The composite exhibits exceptional heat dissipation capabilities, which is critical for thermal management applications in electronics. Moreover, POE/PW/GNPs/Al₂O₃ composites demonstrate outstanding electrical insulation, enhanced mechanical performance, and efficient solar energy conversion and transportation. Under 80 mW cm⁻² NIR light irradiation, the temperature of the POE/PW/GNPs 5 wt%/Al₂O₃ 40 wt% composite reaches approximately 65 °C, a notable 20 °C improvement when compared with the POE/PW blend. The pragmatic and uncomplicated preparation method, coupled with the stellar performance of the composites, opens a promising avenue and broader possibility for developing flexible PCMs for solar conversion and thermal storage applications. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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20 pages, 22215 KiB

Open AccessArticle

Impact Energy Dissipation and Quantitative Models of Injection Molded Short Fiber-Reinforced Thermoplastics

by Quan Jiang, Tetsuo Takayama and Akihiro Nishioka

Polymers 2023, 15(21), 4297; https://doi.org/10.3390/polym15214297 - 1 Nov 2023

Cited by 3 | Viewed by 1226

Abstract

Glass short fiber-reinforced thermoplastics (SGFRTP) are used to reduce carbon dioxide emissions from transportation equipment, especially household vehicles. The mechanical properties required for SGFRTP include flexural strength, impact resistance, etc. In particular, impact resistance is an important indicator of the use of SGFRTP. For this study, a mechanical model was developed to explain the notched impact strength of SGFRTP injection molded products in terms of their interfacial shear strength. The values obtained from the model show good agreement with the experimentally obtained results (R² > 0.95). Results also suggest that the model applies to different fiber orientation angle and a range of fiber lengths in the molded product that are sufficiently shorter than the critical fiber length. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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19 pages, 6811 KiB

Open AccessArticle

Mechanical Anisotropy of Injection-Molded PP/PS Polymer Blends and Correlation with Morphology

by Tetsuo Takayama and Rin Shibazaki

Polymers 2023, 15(20), 4167; https://doi.org/10.3390/polym15204167 - 20 Oct 2023

Viewed by 1277

Abstract

The molecular orientation formed by melt-forming processes depends strongly on the flow direction. Quantifying this anisotropy, which is more pronounced in polymer blends, is important for assessing the mechanical properties of thermoplastic molded products. For injection-molded polymer blends, this study used short-beam shear testing to evaluate the mechanical anisotropy as a stress concentration factor, and clarified the correlation between the evaluation results and the phase structure. Furthermore, because only shear yielding occurs with short-beam shear testing, the yielding conditions related to uniaxial tensile loading were identified by comparing the results with those of three-point bending tests. For continuous-phase PP, the phase structure formed a sea-island structure. The yield condition under uniaxial tensile loading was interface debonding. For continuous-phase PS, the phase structure was dispersed and elongated in the flow direction. The addition of styrene–ethylene–butadiene–styrene (SEBS) altered this structure. The yielding condition under uniaxial tensile loading was shear yielding. The aspect ratio of the dispersed phase was found to correlate with the stress concentration factor. When the PP forming the sea-island structure was of continuous phase, the log-complex law was sufficient to explain the shear yield initiation stress without consideration of the interfacial interaction stress. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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17 pages, 2893 KiB

Open AccessArticle

Experimental Development of an Injection Molding Process Window

by Mason Myers, Rachmat Mulyana, Jose M. Castro and Ben Hoffman

Polymers 2023, 15(15), 3207; https://doi.org/10.3390/polym15153207 - 28 Jul 2023

Cited by 1 | Viewed by 2192

Abstract

Injection molding is one of the most common and effective manufacturing processes used to produce plastic products and impacts industries around the world. However, injection molding is a complex process that requires careful consideration of several key control variables. These variables and how they are utilized greatly affect the resulting polymer parts of any molding operation. The bounds of the acceptable values of each Control Process Variable (CPV) must be analyzed and delimited to ensure manufacturing success and produce injected molded parts efficiently and effectively. One such method by which the key CPVs of an injection molding operation can be delimited is through the development of a process window. Once developed, operating CPVs at values inside the boundaries of the window or region will allow for the consistent production of parts that comply with the desired Performance Measures (PM), promoting a stable manufacturing process. This work proposes a novel approach to experimentally developing process windows and illustrates the methodology with a specific molding operation. A semicrystalline material was selected as it is more sensitive to process conditions than amorphous materials. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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11 pages, 2891 KiB

Open AccessArticle

High-Temperature Response Polylactic Acid Composites by Tuning Double-Percolated Structures

by Haiwei Yao, Rong Xue, Chouxuan Wang, Chengzhi Chen, Xin Xie, Pengfei Zhang, Zhongguo Zhao and Yapeng Li

Polymers 2023, 15(1), 138; https://doi.org/10.3390/polym15010138 - 28 Dec 2022

Cited by 2 | Viewed by 1396

Abstract

Due to the properties of a positive temperature coefficient (PTC) effect and a negative temperature coefficient (NTC) effect, electrically conductive polymer composites (CPCs) have been widely used in polymer thermistors. A dual percolated conductive microstructure was prepared by introducing the polybutylene adipate terephthalate phase (PBAT) into graphene nanoplatelets (GNPs)-filled polylactic acid (PLA) composites, intending to develop a favorable and stable PTC material. To achieve this strategy, GNPs were selectively distributed in the PBAT phase by injection molding. In this study, we investigated the crystallization behavior, electrical conductivity, and temperature response of GNP-filled PLA/PBAT composites. The introduction of GNPs into PLA significantly increased PLA crystallization capacity, where the crystallization onset temperature (T_o) is raised from 116.7 °C to 134.7 °C, and the crystallization half-time (t_1/2) decreases from 35.8 min to 27.3 min. The addition of 5 wt% PBAT increases the electrical conductivity of PLA/PBAT/GNPs composites by almost two orders of magnitude when compared to PLA/GNPs counterparts. The temperature of the heat treatment is also found to play a role in affecting the electrical conductivity of PLA-based composites. Increasing crystallinity is favorable for increasing electrical conductivity. PLA/PBAT/GNPs composites also show a significant positive temperature coefficient, which is reflected in the temperature–electrical resistance cycling tests. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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14 pages, 4432 KiB

Open AccessArticle

Improving Thermal Conductivity of Injection Molded Polycarbonate/Boron Nitride Composites by Incorporating Spherical Alumina Particles: The Influence of Alumina Particle Size

by Chuxiang Zhou, Yang Bai, Huawei Zou and Shengtai Zhou

Polymers 2022, 14(17), 3477; https://doi.org/10.3390/polym14173477 - 25 Aug 2022

Cited by 8 | Viewed by 2353

Abstract

In this work, the influences of alumina (Al₂O₃) particle size and loading concentration on the properties of injection molded polycarbonate (PC)/boron nitride (BN)/Al₂O₃ composites were systematically studied. Results indicated that both in-plane and through-plane thermal conductivity of the ternary composites were significantly improved with the addition of spherical Al₂O₃ particles. In addition, the thermal conductivity of polymer composites increased significantly with increasing Al₂O₃ concentration and particle size, which were related to the following factors: (1) the presence of spherical Al₂O₃ particles altered the orientation state of flaky BN fillers that were in close proximity to Al₂O₃ particles (as confirmed by SEM observations and XRD analysis), which was believed crucial to improving the through-plane thermal conductivity of injection molded samples; (2) the presence of Al₂O₃ particles increased the filler packing density by bridging the uniformly distributed BN fillers within PC substrate, thereby leading to a significant enhancement of thermal conductivity. The in-plane and through-plane thermal conductivity of PC/50 μm-Al₂O₃ 40 wt%/BN 20 wt% composites reached as high as 2.95 and 1.78 W/mK, which were 1183% and 710% higher than those of pure PC, respectively. The prepared polymer composites exhibited reasonable mechanical performance, and excellent electrical insulation properties and processability, which showed potential applications in advanced engineering fields that require both thermal conduction and electrical insulation properties. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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22 pages, 7645 KiB

Open AccessEditor’s ChoiceArticle

Development of an Injection Molding Process for Long Glass Fiber-Reinforced Phenolic Resins

by Robert Maertens, Wilfried V. Liebig, Kay A. Weidenmann and Peter Elsner

Polymers 2022, 14(14), 2890; https://doi.org/10.3390/polym14142890 - 16 Jul 2022

Cited by 5 | Viewed by 3350

Abstract

Glass fiber-reinforced phenolic resins are well suited to substitute aluminum die-cast materials. They meet the high thermomechanical and chemical demands that are typically found in combustion engine and electric drive train applications. An injection molding process development for further improving their mechanical properties by increasing the glass fiber length in the molded part was conducted. A novel screw mixing element was developed to improve the homogenization of the long fibers in the phenolic resin. The process operation with the mixing element is a balance between the desired mixing action, an undesired preliminary curing of the phenolic resin, and the reduction of the fiber length. The highest mixing energy input leads to a reduction of the initial fiber length L₀ = 5000 μm to a weighted average fiber length of L_p = 571 μm in the molded part. This is an improvement over L_p = 285 μm for a short fiber-reinforced resin under comparable processing conditions. The mechanical characterization shows that for the long fiber-reinforced materials, the benefit of the increased homogeneity outweighs the disadvantages of the reduced fiber length. This is evident from the increase in tensile strength from σ_m = 21 MPa to σ_m = 57 MPa between the lowest and the highest mixing energy input parameter settings. Full article

(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)

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