Thermoplastic Processing Research Articles

Aqu‐Thermoplastics: Recycling Plastics with Water

AbstractRecycling of real waste plastics with diverse composition is extremely difficult. Herein, an eco‐friendly and easy‐to‐operate strategy is demonstrated to facilitate the recycling of plastic composites and mixtures by using only water. An aqu‐thermoplastic bioplastic (CPp‐TA) is constructed with switchable water solubility and excellent thermoplastic property from natural cellulose. CPp‐TA consisted of the cellulose main chain (C) and two functional groups, internal‐plasticizing group (Pp) and switchable group (TA). It not only has outstanding thermo‐plastic formability, water resistance, and mechanical property to satisfy the daily needs, but also can be easily recycled with water by switching to the water‐soluble state. CPp‐TA can processed into various high‐performance plastic parts, fibers, heat‐sealing packaging, transparent cups, paper‐plastic composites, and aluminum‐plastic composites by conventional thermoplastic processing methods. The obtained CPp‐TA/Al/paper composite exhibits better barrier performance than the famous Tetra Pak with a complex recycling process, and can be easily separated into CPp‐TA, Al foil, and paper by using basic aqueous solution to trigger the water solubility of CPp‐TA. Similarly, CPp‐TA can be effectively separated from plastic mixtures. The recovery yield achieves to 100%. The revolutionary aqu‐thermoplastic materials and water‐recycling strategy markedly reduce the recycling difficulty of intricate plastics and promote the sustainable development.

Bonding strength of short carbon fiber reinforced PA6 composites ultrasonic welding joints

AbstractShort carbon fiber composites have high specific modulus, high specific strength and excellent formability, which are suitable for short‐term and environmentally friendly ultrasonic welding. In this study, ultrasonic welding experiments were conducted on short carbon fiber reinforced PA6 composites using a servo‐driven non‐metallic ultrasonic welder. The weld specimens were analyzed for spot weld morphologies, interfacial bonding strength, failure modes and compressive shear fracture to establish the correlation between weld energy and weld quality. The results indicate that when the welding energy is 450 J, the short carbon fibers are interlaced at the interface, which has a pinning effect, thereby enhancing the joint strength reaching 2990 N, and the welding efficiency reaches 46%. Besides, the compressive shear section is divided into regions. The proportion of heat and area in different compressive shear regions are quantitatively analyzed, and the calculation model of joint strength is proposed. Meanwhile, the correlation between welding energy and its correlation, as well as three different shear failure modes, is obtained. This work is helpful for the optimization of carbon fiber reinforced thermoplastic (CFRTP) ultrasonic welding process parameters and the evaluation of joint strength.Highlights A special fixture for ultrasonic welding was designed to optimize the welding energy process of ultrasonic welding CFRTP, and the properties of ultrasonic welded joints were analyzed. When the welding energy is 450 J, a high shear strength welded joint of 2990 N was successfully prepared. The shear fracture of the welded joint was successfully obtained by designing a special clamp for compression shearing. The welding area was qualitatively divided according to the temperature measurement results of the interface center. In addition, the heat and area ratio of different zones in the compression‐shearing area under different welding energy were quantitatively analyzed, and the calculation model of joint strength was proposed. At the same time, the welding energy and its correlation, as well as three different shear failure modes were obtained. The short fiber distribution characterization and pores effect on the joint's strength were analyzed. The appearance of porosity defects has a significant weakening effect on the welded joint.

Optimization of thermoplastic composites process parameters based on robotic fiber placement

Optimization of thermoplastic composites process parameters based on robotic fiber placement

Application of Poly(lactic Acid) Composites in the Automotive Sector: A Critical Review.

The introduction of bio-based matrices in automotive applications would, in principle, increase their sustainability and, in case the use of secondary raw materials is also involved, even result in reduced resource depletion. The bio-based polymer composite matrix that has been mainly brought forward towards industrial application is poly(lactic acid) (PLA), which has often been proposed as the replacement for matrices based on polyolefins in fields such as packaging and short-term commodities since, in general, it matches the needs for conventional thermoplastic production processes. The passage to the automotive sector is not obvious, though: problems affecting durability, the relation with water and the environment, together with the requirement for outstanding mechanical and impact performance appear very stringent. On the other hand, PLA has obtained durable success in additive manufacturing as a competitor for acrylonitrile butadiene styrene (ABS). Also, the perspective for 3D and 4D printing does not appear to be confined to bare prototyping. These contrasting pieces of evidence indicate the necessity to provide more insight into the possible development of PLA use in the automotive industry, also considering the pressure for the combined use of more sustainable reinforcement types in automotive composites, such as natural fibers.

Analysis of emission of volatile organic compounds and thermal degradation in investment casting using fused deposition modeling (FDM) and three-dimensional printing (3DP) made of various thermoplastic polymers.

The study examined the degradation process of various types of polymers used to form models using the fused deposition modeling (FDM) and three-dimensional printing (3DP) methods and used in the investment casting method. Commercial filaments made of polylactide (PLA), acrylonitrile butadiene styrene terpolymer (ABS), high-impact polystyrene (HIPS), polyamide 12 (PA12), poly(methyl methacrylate) (PMMA), and polypropylene (PP) were used to produce gypsum molds. The assessment included organic volatile compounds (VOCs) released during mold heating and model degradation, which is characteristic of this technological process. The screening qualitative chromatographic analysis of decomposition products sampled from various points of the production hall made it possible to define potential threats related to the processing of selected polymers and the necessary preventive measures. Furthermore, passive diffusion-type samplers were used at the sampling stage of VOCs emitted to the gaseous phase to reduce nuisance and user interference. Studies have been completed to characterize the thermoplastic polymer degradation process. The coupled thermogravimetry (TGA) with analysis of gaseous products by infrared spectroscopy with Fourier transformation (FT-IR) has been used. The presented results are the first to compare and rate the use of this still-developing novel aspect of castings by the method of fused models.

Synthesis and Characterization of Rebondable Polyurethane Adhesives Relying on Thermo-Activated Transcarbamoylation.

Dynamic polymer networks combine the noteworthy (thermo)mechanical features of thermosets with the processability of thermoplastics. They rely on externally triggered bond exchange reactions, which induce topological rearrangements and, at a sufficiently high rate, a macroscopic reflow of the polymer network. Due to this controlled change in viscosity, dynamic polymers are repairable, malleable, and reprocessable. Herein, several dynamic polyurethane networks were synthetized as model compounds, which were able to undergo thermo-activated transcarbamoylation for the use in rebondable adhesives. Ethylenediamine-N,N,N',N'-tetra-2-propanol (EDTP) was applied as a transcarbamoylation catalyst, which participates in the curing reaction across its four -OH groups and thus, is covalently attached within the polyurethane network. Both bond exchange rate and (thermo)mechanical properties of the dynamic networks were readily adjusted by the crosslink density and availability of -OH groups. In a last step, the most promising model compound was optimized to prepare an adhesive formulation more suitable for a real case application. Single-lap shear tests were carried out to evaluate the bond strength of this final formulation in adhesively bonded carbon fiber reinforced polymers (CFRP). Exploiting the dynamic nature of the adhesive layer, the debonded CFRP test specimens were rebonded at elevated temperature. The results clearly show that thermally triggered rebonding was feasible by recovering up to 79% of the original bond strength.

Manufacturing of hexagonal cross-section thermoplastic matrix composite parts with automatic filament winding system

Thermoplastic filament winding is a flexible manufacturing method typically used in the production of cylindrical composite structures, allowing for in-situ consolidation without the need for a second consolidation step. The objective of this study is to produce non-cylindrical geometries, typically manufactured using thermoset matrix composites according to the literature, using the thermoplastic filament winding process. For this purpose, glass fiber (GF) reinforced polypropylene (PP) prepreg tapes were used to produce hexagonal cross-section thermoplastic composite parts. The critical process parameters; hot-air heater nozzle temperature, compression roller pressure, the linear speed of mandrel rotation, and corner radius of the mandrel, were determined using the Taguchi experimental design method. The interlaminar shear strength (ILSS) and maximum compressive strength (σmax) values were obtained as 211 MPa and 49.40 MPa as maximum, respectively. ANOVA analysis showed that the corner radius had the most significant impact on ILSS, while mandrel rotation speed and temperature were critical for σmax.

Influence of plasticisation during foam injection moulding on the melt viscosity and fibre length of long glass fibre-reinforced polypropylene

Abstract The processing of long glass fibre-reinforced thermoplastics results in considerable fibre damage, particularly during plasticising. By using thermoplastic foam injection moulding (FIM) with a constant blowing agent atmosphere, fibre damage during plasticisation can be reduced. This can be attributed to the reduction of the melt viscosity on the one hand and the influence of the melting behaviour on the other. Therefore, the influence of the FIM and the process parameters on the fibre length and the fibre length distribution are analysed and compared with the influence of the process parameters on the melt viscosity.

ScCO2-processed thermoplastic starch/chitosan oligosaccharide blown films and their oxygen barrier or antibacterial applications

Abstract Antibacterial and oxygen barrier films were inventively prepared by blending very small loadings (<2 wt%) of chitosan oligosaccharide (COS) or chitosan (CS) in thermoplastic starch (TPS) and/or processing with supercritical carbon dioxide (scCO2). Oxygen transmission rates (OTR) and free-volume-hole (FVH) characteristics of scCO2-processed TPS/COS and TPS/CS blown films diminish to a minimum, as their COS or CS approach a specific compatibility limit content. The minimum OTR and FVH characteristics of scCO2-processed TPS/COS films are somewhat smaller than those of corresponding TPS/COS films without scCO2-assistance, and decrease further with decreasing COS molecular weights. The minimum OTR values of scCO2-processed TPS/COS blown films with COS’s molecular weight of 200 and 500 are only 4.1 and 4.5 cm3/m2 × day × atm, respectively, and their antibacterial rates of Staphylococcus aureus are ≥97 %, which make them as promising antibacterial and oxygen barrier films having OTR ≦ 5 cm3/m2 × day × atm. Among other things, longitudinal or transversal tensile strengths acquired for the properly scCO2-processed TPS/COS or TPS/CS films are ∼30 to ∼50 % higher than those of the TPS films. Dynamic mechanical relaxation results of these scCO2-processed reveal that chitosan oligosaccharide or chitosan are compatible with TPS, as COS or CS contents are ≤ the compatibility limit value.

Vaterite-based in situ surface modification and process-dependent biocompatibility of laser sintered polypropylene

Polypropylene (PP) rapidly gains scientific attention as fatigue-resistant and lightweight tissue repair and implant material, while emerging laser-sintering based methods for PP processing further allow unlimited versatility of PP specimens and often reduced numbers of process steps, substituting traditional manufacturing approaches. Generally, PP is considered biocompatible for a variety of medical applications while showing superior long-term stability, however, thermoplastic processing of polypropylene may induce the formation of cytotoxic degradation products, necessitating its cytotoxicological assessment. In the present study, PP specimens have been fabricated using warm, quasi-isothermal and complementary cold, non-isothermal powder bed fusion (PBF), allowing processing PP at ambient powder bed temperature of 25 °C for minimizing thermal exposure and the formation of decomposition products. The surface of manufactured specimens has been modified with hybrid coatings consisting of mesoporous inorganic microcrystals of vaterite laden with model biomacromolecules, i.e., fluorescently labelled dextran, demonstrating the stable coating and attachment of dextran-loaded vaterite crystals independent of the applied PBF processing regime. Vaterite coating is degradable and enables the opportunity to endow the surface of PP with sustained release functionalities. Both coated and uncoated specimens demonstrated excellent biocompatibility independent of the applied processing regime, as evaluated in an ex ovo shell-less hen's egg model.

Packing simulation and analysis applied to a thermoplastic composite recycling process

A numerical model of packing applied to rigid objects is presented. It aims at describing a random stack of polymer composite chips in order to model the packing step of an existing recycling technique. The geometric properties of the stack play a major role in the mechanical properties of the recycled products. Short, simple and effective geometric descriptors of the stack are proposed. Their ability to differentiate random stacks is illustrated with an example. Then, a validation is proposed based on experimental data obtained from a bench specially designed for this work. The tests consist in the free fall of square chips. Finally, the developed model is compared to other models (free fall and packing of fibers) in order to enforce its relevance in the simulation of packing of rigid objects.

Pre- and in-process dimensional compensation in the selective thermoplastic electrophotographic process

As a cutting-edge additive manufacturing (AM) technology, the selective thermoplastic electrophotographic process (STEP) has opened up possibilities for mass production with its combination of real engineering plastics and potential high part quality. To improve the accuracy and fidelity of STEP for the most demanding applications, this paper proposes a novel method encompassing both pre-processing and in-process dimensional compensations. Iterative compensation before production is achieved through physics-driven simulation, resulting in input masks that better match the required dimensions at the design level. Layer-wise compensation is implemented during the production process through the laser profiler system, thereby suppressing the accumulation of surface unevenness during printing. With the compensation method proposed in this paper, the maximum distortion during simulated printing is decreased by 86.2%, and surface unevenness is effectively controlled during the printing process.

The technology and current applications of continuous fiber‐reinforced thermoplastic composites

AbstractBecause of its inherent properties, the use of thermoplastic composites is expanding in a number of industries, including aerospace, rail transportation, and wind power generation. However, the development of 2D and 3D reinforced thermoplastic composite structures is hampered by the high viscosity and poor wetting of thermoplastic matrices, resulting in their application being mainly limited to nonload‐bearing components. This article provides a comprehensive overview of the technology and current applications of thermoplastic composites, covering materials, preform structures, manufacturing methods, process parameters, performance, and applications. It also provides an outlook on their future development.Highlights Thermoplastic composite has economic and environmental benefits. Summarized the current technology and application of thermoplastic composites. The manufacturing difficulty is the thermoplastic polymers wet fibers. One promising approach to the issue is prepreg technology. Prepreg technology make 3D thermoplastic composites become possible.

Co‐reinforcing sustainable graphenes from thermoset/thermoplastic wastes for enhanced polypropylene matrix composites in automotive engineering

AbstractTalc is widely used in the automotive industry as a primary reinforcement in part manufacturing. However, its relatively high density, low impact strength, and difficulty in recycling pose challenges. The present study investigates the utilization of graphene grown on talc derived from waste polypropylene (PP) and graphene nanoplatelet obtained from waste tires by recycling and upcycling processes to be used as reinforcing agents in thermoplastic processing by keeping mechanical integrity and part performance properties the same compared to the part used in serial production. The whole value chain was examined by developing compound formulation, scaling up with a high shear mixer, and injection molding of the selected exterior part of the glass front grill with its part performance tests with the real‐case thermal and structural finite element analysis. Regarding the mechanical performance analysis, the developed compound formulation having 9 wt% micron scale talc with graphene nanoparticles and hybrid additive yielded substantial enhancements of 32% and 22% in flexural and tensile strength, respectively, in the homopolymer polypropylene (HomoPP) matrix by achieving 10% weight reduction. With a systematic life cycle assessment study, CO2 reduction was provided by 55% for the selected part by replacing virgin HomoPP with mechanically recycled waste PP originally unknown.

Improving performance of TPU by controlled crosslinking of soft segments

AbstractThermoplastic polyurethanes (TPUs) are a family of thermoplastic elastomers with great properties such as high elongation and excellent chemical and abrasion resistance, which are processable by conventional melting methods. Nevertheless, TPUs lose mechanical properties and thermal stability at higher temperatures. In this work, we designed and synthesized a new TPU with limited crosslinking of the soft segments in order to improve its performance at high temperatures while preserving processability. Additionally, the new TPU maintains its transparency. With the incorporation of 10% trifunctional polyol, the Tg was increased by 7°C, the storage modulus at room temperature (25°C) was improved by 412 MPa (136%), the rubbery plateau was extended by 32°C and the thermal stability was enhanced by 4°C at T5. Moreover, the TPU with controlled crosslinking of the soft segments shows exceptional creep behavior both at room temperature and at 150°C, where the creep rate decreased by 80%. The new TPU shows limited decrease in tensile properties and can be processed by conventional thermoplastic processing techniques.Highlights Design and synthesis of a new TPU with limited crosslinking of the soft segments. Incorporation of the crosslinks into the soft segments preserves system processability. Enhanced mechanical and thermal properties while preserving system transparency. High temperature application window extended by 32°C. Creep rate at 150°C lowered by 80%.

DL‐Isoborneol esters as nontoxic main plasticizers for polyvinyl chloride with improved processability, thermal stability, and mechanical performance

AbstractDL‐Isoborneol is a forestry chemical product that can serve as an intermediate in the synthesis of value‐added plasticizer products. In this study, three kinds of DL‐Isoborneol esters (octanoic acid‐DL‐Isoborneol, decanoic acid‐DL‐Isoborneol ester, and lauric acid‐DL‐Isoborneol ester [LDE]) with different fatty hydrocarbon chains were synthesized via esterification reaction. Fourier transform infrared spectrometer (FT‐IR) and Nuclear magnetic hydrogen spectrum (1H NMR) indicated that DL‐Isoborneol esters were successfully synthesized. The oral toxicity experiment of plasticizers in mice indicated that DL‐Isoborneol esters have toxic doses of 5000 mg/kg and was environmentally friendly and nontoxic. DL‐Isoborneol esters were used as main plasticizers to plasticize polyvinyl chloride (PVC) and compared with commercial plasticizer dioctyl phthalate (DOP). The results showed that DL‐Isoborneol esters could improve thermoplastic processing performance and thermal stability of plasticized PVC than DOP. DL‐Isoborneol esters and PVC showed more excellent compatibility compared with DOP. Tg of plasticized PVC reached 22°C, tensile strength and elongation at break of PVC plasticized with 40 wt% LDE reached 12.90 ± 0.83 MPa and 342 ± 13%, respectively. DL‐Isoborneol esters with improved migration resistance performance and plasticization efficiency can completely replace DOP as main plasticizers for PVC.Highlights DL‐Isoborneol esters with different fatty hydrocarbon chains were synthesized. DL‐Isoborneol esters have toxic doses of 5000 mg/kg and are nontoxic. DL‐Isoborneol esters can be used as main plasticizer for PVC. Plasticized PVC with improved processability. DOP can be completely replaced by DL‐Isoborneol esters.

Wastewater phosphorus enriched algae as a sustainable flame retardant in polylactide

Revolutionizing our polymer industry for adaption to a sustainable carbon circular economy has become one of today's most demanding challenges. Exploiting renewable resources to replace fossil-fuel—based plastics with biopolymers such as poly(lactic acid) (PLA) is inevitable while using waste streams as a raw material resource at least is promising. When it comes to using PLA as technical polymer, its high flammability must be addressed by flame retardants compatible with the thermoplastic processing of PLA and its compostability. This study proposes microalgae enriched with phosphorus from wastewater (P-Algae) as an elegant way towards a kind of sustainable organophosphorus flame retardant. The concept is demonstrated by investigating the processing, pyrolysis, flammability, and fire behavior of PLA/P-Algae, while varying the P-Algae content and comparing P-Algae with four alternative bio-fillers (phosphorylated lignin, biochar, thermally treated sewage sludge, and metal phytate) with different P-contents as meaningful benchmarks.

Challenges to Improve Extrusion-Based Additive Manufacturing Process of Thermoplastics toward Sustainable Development.

This review aims to present the different approaches to lessen the environmental impact of the extrusion-based additive manufacturing (MEX) process of thermoplastic-based resins and protect the ecosystem. The benefits and drawbacks of each alternative, including the use of biomaterials or recycled materials as feedstock, energy efficiency, and polluting emissions reduction, have been examined. First, the technological option of using a pellet-fed printer wascompared to a filament-fed printer. Then, common biopolymers utilized in MEX applications are discussed, along with methods for improving the mechanical properties of associated printed products. The introduction of natural fillers in thermoplastic resins and the use of biocomposite filaments have been proposed to improve the specific performance of printed items, highlighting the numerous challenges related to their extrusion. Various polymers and fillers derived from recycling are presented as feeding raw materials for printers to reduce waste accumulation, showing the inferior qualities of the resulting goods when compared to printed products made from virgin materials. Finally, the energy consumption and emissions released into the atmosphere during the printing process are discussed, with the potential for both aspects to be controlled through material selection and operating conditions.

Theoretical Assessment of the Environmental Impact of the Preheating Stage in Thermoplastic Composite Processing: A Step toward Sustainable Manufacturing

Theoretical Assessment of the Environmental Impact of the Preheating Stage in Thermoplastic Composite Processing: A Step toward Sustainable Manufacturing

Microstructure evolution and mechanical properties of β/γ-TiAl alloy during high-rate near-isothermal multidirectional forging

The microstructure of β/γ-TiAl alloy was characterized and analyzed in various deformation regions during a high-rate near-isothermal multidirectional forging (HR-NIMDF) process in this study. The results indicate that the localized precipitation of the B2 phase occurs within the large lamella microstructure through DRX and heterogeneous exsolution decomposition mechanism in the stagnant zone. The majority of mixed fine-grained microstructures (α2/γ/B2), with a grain diameter smaller than 1 μm, were formed under an appropriate stress-temperature coupling field. In the central region of the large deformation zone, a small twisted lamellar microstructure with low B2 phase content is observed, suggesting that HR-NIMDF can efficiently decompose the (α2/γ) lamellar structure and achieve refined grain microstructures. After undergoing HR-NIMDF, the β/γ-TiAl alloy exhibits a low tough-brittle transition temperature and an elongation of 7 % at 650 °C, with an ultimate tensile strength of 862.6 MPa. At 700 °C, the elongation increases to 55.4 %, while the ultimate tensile strength decreases to 653.8 MPa. Moreover, this study demonstrates that when the plastic deformation degree is insufficient and the adiabatic warming effect is relatively pronounced, significant precipitation of the B2 phase leads to a reduction in DRX extent within the material, ultimately resulting in the formation of large residual (α2/γ) lamellar microstructure. The unsynchronized thermal-force coupling relationship between the precipitation of the B2 phase and DRX holds significant implications for advancing and refining the thermoplastic deformation process of β/γ-TiAl alloy.