Technical Polymers Research Articles

Sustainable Compositions and 3D Printing Technologies for Characterizing and Optimizing Recycled PETG

The packing industry makes extensive use of terephthalate polyesters because of their chemical durability and optical qualities. Examples of these materials are polyethylene terephthalate (PET) and glycol-modified PET (PETG). They also supply building materials, medical technology, technical polymers, and the textile sector. PET is made of terephthalic acid as well as ethylene glycol, whereas 30% of the diol moles in PETG are replaced with CHDM during synthesis. Detailed structural analyses of polyethylene terephthalate glycol-modified (PETG) are presented in this study. In two directions, PETG square blocks were tested with a load of 12,200 N to determine their durability and mechanical response. This block experienced a total deformation of 0.2318 mm under vertical loading, with the outer layer experiencing 33.93 MPa, and the middle layer experiencing 23.148 MPa. According to its performance under vertical stress, PETG had a maximum fatigue life of approximately 572,540 cycles and a minimal safety factor of 0.035116. A deformation of 0.23192 mm was recorded under horizontal loading. The bottom layer had a stress of 46.317 MPa and the top layer had a stress of 20.174 MPa, with a better fatigue life of 616,880 cycles and a safety factor of 0.35979.

PECVD and PEALD on polymer substrates (part I): Fundamentals and analysis of plasma activation and thin film growth

AbstractThis feature article presents recent results on the analysis of plasma/polymer interactions and the nucleation of ultra‐thin plasma films on polymeric substrates. Because of their high importance for the understanding of such processes, in situ analytical approaches of the plasma volume as well as the plasma/substrate interfaces are introduced before the findings on plasma surface chemistry. The plasma activation of polymeric substrates is divided into the understanding of fundamental processes on model substrates and the relevance of polymer surface complexity. Concerning thin film nucleation and growth, both plasma‐enhanced chemical vapor deposition and plasma‐enhanced atomic layer deposition processes as well as the combination of both processes are considered both for model substrates and technical polymers. Based on the comprehensive presentation of recent results, selective perspectives of this research field are discussed.

Impact of peanut shells, olive pomace, and plaster on the dielectric properties of PA6

Polyamide 6 (PA6) is among the most widely used technical polymers due to its excellent balance between performance and cost. The diversity of its applications reflects its main qualities (good mechanical properties, thermal stability, resistance to many solvents and bases, etc.). PA6 is often used as an electrical insulator, and in this study, we have shown that we can keep this property by using Plaster (PL) as reinforcement, just as we can by incorporating bio-reinforcements including peanut shell powder (PSP) or olive pomace powder (OPP) to modify this behavior. This was achieved by studying the electrical and dielectric properties of PA6 and PA6/PSP, PA6/OPP, and PA6/PL composites using impedance spectroscopy in the glass transition region ranging from 20°C to 50°C in a range frequency 1Hz - 1MHz. The results show that the PA6/PSP and PA6/OPP composites exhibited low resistance; therefore, very good electrical conductivity was recorded. However, PA6/PL inherits almost the same characteristics as PA6. The present study asserts that the presence of charges in the composite's interfacial region greatly influences the electrical and dielectric behavior and that this behavior is strongly affected near the Tg.

Biocarbon-based sustainable reinforcing system for technical polymers. The structure-properties correlation between polycarbonate (PC) and polybutylene terephthalate (PBT)-based blends containing acrylonitrile-butadiene-styrene (ABS)

The sustainable filler system consisting of biocarbon (BC) particles and short basalt (BF) and carbon (CF) fibers was used as the reinforcement for PC/ABS and PBT/ABS type blends. The melt blending procedure includes the preparation of hybrid composite samples, where part of the fibrous filler was replaced by biocarbon powder. Reference samples were prepared with BF and CF fibers. For all samples, the content of the fillers was 20 wt%. The prepared materials were manufactured using the injection molding technique, while during this procedure, different types of standard testing samples were molded, including application samples. For part of the samples, the thermo-oxidative heat aging procedure was applied. All samples were subjected to characterization procedures, including mechanical and thermomechanical tests and structure properties examination. The comparison of the modulus value for BF/BC composites shows a modulus increase of 100%, from 2.5 GPa to over 5.0 GPa for both types of composites (PC and PBT), and the stiffness for CF/BC samples exceeds 6.0 GPa. The increase in thermal resistance compared to the unmodified PBT/ABS matrix was 20 °C for the composite of the BF/BC system and 10 °C for the CF/BC samples. The increase for hybrid samples based on PC/ABS did not exceed 12 °C. The obtained results confirmed that the presence of BC particles was not leading to thermal degradation of the matrix blend; however, the mechanical performance of the hybrid composites was slightly lower. As a result of the heat aging procedure, the properties deterioration was more significant for PC/ABS-based samples since the mechanical performance was reduced after 1000 h of thermo-oxidation. However, the thermal analysis and structure observations did not confirm any significant changes in the macromolecular structure of the prepared materials, which confirmed the possible use in demanding applications.

Performance Spectrum of Home-Compostable Biopolymer Fibers Compared to a Petrochemical Alternative

Manufacturers of technical polymers must increasingly consider the degradability of their products due to the growing public interest in topics such as greenhouse gas emissions and microplastic pollution. Biobased polymers are part of the solution, but they are still more expensive and less well characterized than conventional petrochemical polymers. Therefore, few biobased polymers with technical applications have reached the market. Polylactic acid (PLA) is the most widely-used industrial thermoplastic biopolymer and is mainly found in the areas of packaging and single-use products. It is classed as biodegradable but only breaks down efficiently above the glass transition temperature of ~60 °C, so it persists in the environment. Some commercially available biobased polymers can break down under normal environmental conditions, including polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT) and thermoplastic starch (TPS), but they are used far less than PLA. This article compares polypropylene, a petrochemical polymer and benchmark for technical applications, with the commercially available biobased polymers PBS, PBAT and TPS, all of which are home-compostable. The comparison considers processing (using the same spinning equipment to generate comparable data) and utilization. Draw ratios ranged from 29 to 83, with take-up speeds from 450 to 1000 m/min. PP achieved benchmark tenacities over 50 cN/tex with these settings, while PBS and PBAT achieved over 10cN/tex. By comparing the performance of biopolymers to petrochemical polymers in the same melt-spinning setting, it is easier to decide which polymer to use in a particular application. This study shows the possibility that home-compostable biopolymers are suitable for products with lower mechanical properties. Only spinning the materials on the same machine with the same settings produces comparable data. This research, therefore, fills the niche and provides comparable data. To our knowledge, this report is the first direct comparison of polypropylene and biobased polymers in the same spinning process with the same parameter settings.

Recycling and the end of life assessment of fluoropolymers: recent developments, challenges and future trends.

Herein, we present the state of the art technology on the recycling, reuse, thermal decomposition (by thermolysis, thermal processing, flash pyrolysis, smoldering, open burning, open-air detonation, and incineration), and the life cycle assessment of fluoropolymers (FPs, ranging from poly(tetrafluoroethylene), PTFE, and poly(vinylidene fluoride), PVDF, to various fluorinated copolymers based on VDF and TFE). FPs are niche specialty polymers endowed with exceptional properties and have found many applications in high-tech industries. However, compared to other polymers, the reuse of FPs is still not well-established and is in its infancy. Accordingly, their recycling has attracted increasing interest, even reaching the pilot stage. In addition, recently, several studies have been reported on vitrimers, which are regarded as polymers ranking between thermosets and thermoplastics. In this case, although many articles have reported to date on the thermal degradation of these technical polymers, intensive efforts have been devoted to avoiding the release of low molar mass oligomers and per- and poly-fluoroalkyl substances (PFAS, and especially polymerisation aids such as perfluorooctanoic acid (PFOA) and its alternatives), while various reports demonstrated the complete decomposition of PTFE, leading to the formation of TFE (and hexafluoropropylene or octafluorocyclobutane to a lesser extent). Incineration is one of only a few technologies that can potentially degrade FPs and completely degrade PTFE and other PFAS from 850 °C. Recent studies on the mineralisation of FPs under subcritical water represent an interesting approach to close the loop of the fluorine chemistry cycle. Because of the high molar masses (several million for PTFE) and thermal, chemical, photochemical, and hydrolytic inertness and biological stability of FPs, it has been clearly evidenced that they satisfy the 13 accepted regulatory assessment criteria to be considered as polymers of low concern.

Study of the optical, thermal, morphological and mechanical characteristics of a laser weldable fiber reinforced polymer

AbstractIn recent years, varied industrial users such as the automotive and electronic manufacturers, have greatly expanded the application of technical polymers, exploring the lower weight, improved moldability of complex parts and good mechanical performance that these materials can provide, especially when reinforced with fibers. Among these materials, polybutylene terephthalate reinforced with 30% glass fiber, designated as PBT GF30, is highly interesting, since it combines excellent mechanical properties with watertightness, allowing PBT GF30 to be used in the encapsulation of sensitive electronic elements. However, to maintain access, PBT GF30 products always require the use of joints, which are often created using laser welding. This work presents a detailed characterization of the thermal, optical, mechanical, and morphological characteristics of PBT‐GF30 suitable for laser welding, supported by a numerical analysis. This process allowed to determine the influence of thermal energy on the behavior of the material and thus fully understand the mechanical response of the material after laser welding. Testing of the PBT GF30 in the as received state confirmed a fusion temperature of 225°C and large energy absorption for wavelengths around 1000 nm. Exposure to large temperatures leads to increased fiber exposure and matrix degradation, with a deleterious effect on the mechanical properties. When treated at the highest temperature under consideration, the material exhibited a reduction of 66% in its ultimate tensile stress, 67% in the yield at failure, 45% in the Young's modulus and 44% in the stress intensity factor. Hardness was less affected by the temperature increase. From the numerical model for the tensile and the compact tension tests, it was possible to find a good degree of convergence. This material was generally found suitable for laser welding processes and the determined useful to support the modeling the behavior of laser welded joints.

Polyamide/sepiolite Nanocomposites for application in Additive Manufacturing processPolyamide/sepiolite Nanocomposites for application in Additive Manufacturing process

Additive manufacturing includes a series of technologies where a three-dimensional object is fabricated by the superposition of different layers of material. From all this technologies, fused filament fabrication (FFF) may the most mature approach. This technology has been used mainly for rapid prototyping, but it starts to be implemented at the industrial level due to the low energy consumption and greater efficiency in the use of raw materials. Currently, the most used polymers in FFF process are the polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). However, their mechanical properties and service temperature are not good enough to be used in applications where high technical demands are recquired. Due to these shortcomings, scientists have focused on other technical polymers such polyether ether ketone (PEEK) and polyetherimide (PEI). Other approach to improve mechanical performance of traditional materials is the use of fibers or nanofibers, which allows printed parts with new functionalities and/or improved properties. In this study a needle-like nanoclay has been used for obtaining bio-polyamide nanocomposites, specially prepared for FFF application. The final printed parts showed good dimensional stability and good mechanical properties, which place them between the conventional (PLA and ABS) and the technical materials (PEEK and PEI).

Bio-inspired 3D micro structuring of a liver lobule via direct laser writing: A comparative study with SU-8 and SUEX

Real biological tissues show a great variety of different geometric morphologies with special features on different geometric scales. An interesting example is the liver lobule that is the basic subunit of a liver. The lobule is a quasihexagonal macroscopic structure with periodic like so-called sinusoidal elements with structural features on the micro- and macroscale made of proteins, cells, and fluids. Various tools from micromachining and nanotechnology have demonstrated their capabilities to construct micromorphologies precisely, but even the reconstruction of such a system in technical polymers is challenging. In this work, the rapidly evolving technique of multiphoton polymerization has been explored for the construction of a scaffold that mimics the micromorphology of the liver with high resolution and detail up to the millimeter scale. At the end, a highly complex fluidically perfusable structure was achieved and simulations showed that the occurring shear stress, fluid velocity, and stream lines are comparable to the native liver lobule. Hereby, the photoresists SU-8 and SUEX TDFS were compared in terms of their processability, achievable resolution, and suitability for the intended application. Our results have shown that SUEX needs lower writing velocities but is easier to process and achieves a considerable higher resolution than SU-8. The scaffold could provide a base frame with a geometrically defined morphology for hepatic cells to adhere to, which could act as a starting point for cells to build new liver tissue for further integration in more complex systems.

Improving the Tribological Properties of Technical Polymers with Metal Sulphide Compounds

Technical thermoplastic materials (e.g., PEEK, PPA and POM) are widely used for tribological applications combined with different filler systems (e.g., glass- or carbon fibres) because of their excellent mechanical properties. The friction and wear behaviour of thermoplastics can be specifically improved by solid lubrication systems such as graphite, PTFE and MoS2. Besides these systems, others such as WoS2 and MnS are becoming scientifically interesting. This work investigates the influence of different solid lubricants—alternative metal sulphides and polymer-based—in combination with different glass fibre contents on the tribological behaviour of unfilled PEEK and glass fibre-filled PPA. For this purpose, compounds were produced and injection-moulded into tribological test specimens that were subsequently tested. It is particularly evident for both matrix materials that the solid lubricant SLS 22 shows a 25% wear rate reduction when compared to MoS2 and, in addition, the proportion of fibre content in PPA shows an additional wear rate reduction by a factor of 10. The friction level could be kept at a similar level compared to the usually utilised solid lubricants. The investigations showed the potential use of metal sulphide filler systems in high-performance thermoplastic with enhanced tribological properties as alternatives to the well-established solid lubricants.

Mechanical properties and drop-weight impact performance of injection-molded HDPE/birch fiber composites

Natural-fiber-reinforced composites offer various advantages over synthetic composites, including low density, useful mechanical properties and environmental friendliness. In spite of the progress achieved in the field, the mechanical performance of these composite materials has yet to be fully characterized, particularly in terms of impact resistance. In this study, we measured the drop weight impact, Izod impact strength, hardness, tensile strength and elastic modulus of birch-fiber-reinforced HDPE obtained by injection molding. Drop weight impact energy absorbed was constant and independent of fiber content whereas impact strength was inversely proportional to fiber content. Material toughness decreased slightly at 40% fiber. The Shore D hardness of virgin HDPE increased from 50.6 at 0% fiber to 74.6 at 30% fiber. The improvement of the elastic modulus of a composite containing 40% fiber was 27.2% superior to that reported for similar material made by compression molding. The corresponding improvement in tensile strength was superior by 19.7%. Birch-fiber-reinforced HDPE could be an adequate alternative to technical polymers widely used in several industrial sectors.

Evaluation of adhesion properties of lignin-epoxy adhesives in structural wood applications for automotive components

The use of sustainable hybrid components is an important topic in lightweight automotive applications. Wood being a renewable material, when used in combination with other materials such as technical polymers, offers a high potential for producing hybrid components and the implementation of innovative lightweight automotive materials. The feasibility of wood-based hybrid automotive components strongly depends on the properties of the interface between wood, lignin as a renewable coupling agent, and technical polymers. This paper investigates the macromolecular reactions and the bonding area in biobased epoxy adhesives for a specific influence on the performance of structural automotive wood components. Therefore, a typical bisphenol A diglycidyl ether epoxy adhesive was modified with lignosulphonate to increase the penetration depth. The composites were characterized by thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy to validate the crosslinking of the macromolecules and the thermal stability of the adhesive. In the next step, a layer-by-layer composite was built up with the biobased adhesive and 1 mm beech veneer. The bonding area was characterized by scanning electron microscopy and compression tests.

A novel class of high molecular weight multifunctional antioxidants for polymers based on thiol-ene click reaction

Novel bifunctional antioxidants (AO) with high molecular weight were successfully synthesized by two-step free-radical thiol-ene click reaction and transesterification. The structures of the stabilizers were confirmed by 1H NMR spectra and Fourier Transform Infrared Spectrometry (FTIR). Thermal gravimetric analysis (TGA) showed high temperature stability above 300 °C, proving suitability as potential stabilizers for standard and technical polymers. The performance of the bifunctional antioxidants was investigated through oxidation induction time (OIT) and accelerated heat aging of PP compounds in comparison to state of the art stabilizers represented through 2,2′-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and a binary mixture of pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) and dioctadecyl 3,3′-thiodipropionate. Reduced degradation and extended maintenance of mechanical values of PP stabilized through the novel antioxidants during heat aging are due to the high amount of alkyl sulfide groups. Furthermore, a low migration tendency of the high-molecular AO could be determined by FTIR mapping of heat-treated samples.

Compatibility study of support materials within the enzyme-mediated addressing of proteins

Enzyme-mediated addressing is a versatile, specific, energy-efficient, and easy-to-apply method for the formation of coatings and particle arrangements on surfaces. While variability, with respect to particle materials and achievable structures, has received much attention in the past, the equally important aspect of compatible support materials has not yet been considered. This is however an extremely relevant aspect with regard to real-world applications. In particular, technical polymers and metal supports are of supreme importance in sectors such as life-sciences or nanotechnology. This work is designed as an extensive compatibility study for support materials with the enzyme-mediated addressing of proteins. By careful evaluation of produced coating structures, it is shown that most examined metals and polymers, as well as inorganics and wood, can be successfully coated with thin and highly site-specific protein films, opening up manifold new possibilities for the application of the enzyme-mediated addressing in high-tech products.

Smart photoactive soft materials for environmental cleaning and energy production through incorporation of nanophotocatalyst on polymers and textiles

Energy and environment are key issues for the sustainable development of human beings and are also the current and long‐term focuses of scientific research. New energy and environmental technologies in combination with polymer and textile science work to create many additional functions for conventional polymers and fabrics. Therefore, some novel technical polymers and textiles, such as photovoltaic and photocatalytic polymers and textiles, have begun to emerge. Generally, light‐activated chemicals, materials, or processes that are produced or enabled by light and the agent absorbing light starting a photochemical alteration in the system is nominated as photocatalyst. This review firstly introduces the different photoactive materials, their classifications, and degradation mechanism. Then, inorganic semiconductor nanoparticles were selected as the best candidate for the application in soft materials. Finally, a detailed study was provided on both preparations of photoactive soft materials using metal oxide semiconductors and their advantages and applications. This paper will be more helpful for the scientists working in the field of photoactive soft materials.

The Effect of Irradiation on Mechanical and Thermal Properties of Selected Types of Polymers.

This article deals with the influence of electron-beam radiation on the micro-mechanical, thermo-mechanical, and structural properties of selected polymers. In the search for the desired improvement of polymers, it is possible to use, inter alia, one particular possible modification—Namely, crosslinking—Which is a process during which macromolecular chains start to connect to each other and, thus, create the spatial network in the structure. In the course of the treatment of the ionizing radiation, two actions can occur: crosslinking and scission of macromolecules, or degradation. Both these processes run in parallel. Using the crosslinking technology, standard and technical polymers can acquire the more “expensive” high-tech polymeric material properties and, thus, replace these materials in many applications. The polymers that were tested were selected from across the whole spectra of thermoplastics, ranging from commodity polymers, technical polymers, as well as high-performance polymers. These polymers were irradiated by different doses of beta radiation (33, 66, 99, 132, 165, and 198 kGy). The micro-mechanical and thermo-mechanical properties of these polymers were measured. When considering the results, it is obvious that irradiation acts on each polymer differently but, always when the optimal dose was found, the mechanical properties increased by up to 36%. The changes of micro-mechanical and thermo-mechanical properties were confirmed by structural measurement when the change of the micro-hardness and modulus corresponded to the crystalline phase change as determined by X-ray and gel content.

Residual wood polymers facilitate compounding of microfibrillated cellulose with poly(lactic acid) for 3D printer filaments.

Microfibrillated cellulose (MFC) is a fascinating material with an obvious potential for composite reinforcement due to its excellent mechanics together with high specific surface area. However, in order to use this potential, commercially viable solutions to important technological challenges have to be found. Notably, the distinct hydrophilicity of MFC prevents efficient drying without loss in specific surface area, necessitating storage and processing in wet condition. This greatly hinders compounding with important technical polymers immiscible with water. Differently from cellulose, the chemistry of the major wood polymers lignin and hemicellulose is much more diverse in terms of functional groups. Specifically, the aromatic moieties present in lignin and acetyl groups in hemicellulose provide distinctly less polar surface-chemical functionality compared to hydroxyl groups which dominate the surface-chemical character of cellulose. It is shown that considerable advantages in the production of MFC-filled poly(lactic acid) filaments for three-dimensional printing can be obtained through the use of MFC containing residual lignin and hemicellulose due to their advantageous surface-chemical characteristics. Specifically, considerably reduced agglomerations of MFC in the filaments in combination with improved printability and improved toughness of printed objects are achieved.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Dichroic nanocomposites based on polymers and metallic particles: from biology to materials science

AbstractDichroic nanocomposites change their colors when they are viewed through a turning polarizer. In the case of polymer matrices containing inorganic nanoparticles, this color effect originates in anisotropic structures of inorganic moieties, such as uniaxially oriented linear assemblies of spherical nanoparticles or parallel oriented nanorods. The orientation of the particles or particle assemblies, respectively, is induced by the polymer matrix, either through oriented elongated hollow spaces or drawing. Matrices based on biopolymers (e.g. cellulose, polypeptides, chitin) as well as synthetic polymers (e.g. polyethylene, poly(vinyl alcohol)) have been employed. The dichroic colors have been generated so far mainly by silver or gold particles (including nanorods), but also other metals and occasionally also semiconductors (metalloids). Notably, dichroism is also disclosed in optical absorption spectra recorded with polarized light. Dichroism in biopolymer‐based objects with incorporated nanoparticles has been exploited for the cognition of biological fine structures, while dichroic films with technical polymers as matrices have been considered as optical switches in bicolored liquid crystal displays and authenticity cachets for documents, banknotes and packaging films. In this context, micropatterning of dichroic nanocomposites, which has been achieved by local heating procedures of materials composed of metal nanorods, is also of interest. © 2017 Society of Chemical Industry

Production of spherical wax and polyolefin microparticles by melt emulsification for additive manufacturing

Melt emulsification is a top-down approach that so far has been applied in the food industries (cf. homogenization of milk) and in pharmaceutical applications. Within this contribution the applicability of the process for the production of spherical polymer microparticles will be outlined. Size reduction of the polymer raw melt emulsion was realized in a rotor–stator-device. The process is characterized for paraffin and polyethylene (PE) waxes in aqueous environment using Tween 85 as an emulsifier. Process temperature and dispersed phase viscosity have the largest impact on the particle size distribution (PSD): decreasing temperature and viscosity leads to smaller particles. The suitability of the melt emulsification process for technical polymers is demonstrated for polypropylene (PP) emulsified in a continuous hexadecane phase. Polymer particles obtained by the proposed method are promising candidates for advanced powders for additive manufacturing processes like selective laser beam melting (LBM) of polymers. The LBM processability of the obtained PP powders is demonstrated by production of sintered layers.

Improved High Performance Recycling of Polymers by Means of Bi-Exponential Analysis of Their Fluorescence Lifetimes

Technical polymers could be identified by means of their remarkably strong auto fluorescence. The mono-exponentially obtained time constants of fluorescence decay were applied for a rough assignment of the polymeric materials whereas bi-exponential analysis allowed a fine classification such as for special batches and for preceding contaminations. Chemically similar materials such as LDPE (low-density polyethylene), HDPE (high-density polyethylene) and UHDPE (ultrahigh-density polyethylene) could be as well identified as contaminations of mineral oil in PET (polyethylene terephthalate). Furthermore, the fluorescence spectra could be characterized by means of five Gaussian functions in the visible allowing a redundant assignment to the fluorescence lifetimes. Thus, efficient sorting of polymers was possible for high performance recycling.