Thermoplastic polyurethane/clay nanocomposite foam made by batch foaming

The effect of process parameters of foam injection molding on the morphologicalproperties of acrylonitrile butadiene styrene (ABS)-nanoclay polymeric foam has been investigated. Polymethyl methacrylate (PMMA) was used as the compatibilizer between polymeric matrix and nanoclay. Different nanocomposite polymeric foam samples were produced in a chemical foam injection molding process. X-ray diffraction (XRD) test was carried out to analyze the dispersion of nanoclays with different percentages in the polymeric matrix and scanning electron microscopy (SEM) pictures were used to study the cellular structure of nanocomposite foamed samples. The effect of input parameters including nanoclay weight percentage (0, 2, and 4%), Injection Pressure (110, 125, and 140 MPa), and Holding pressure (110, 125, and 140 MPa) on cell density, cell size and expansion ratio of foamed samples have been investigated. Taguchi approach was used for the design of experiments and statistical analysis of results. Based on the results, 2 wt % of nanoclay and injection and holding pressures of 140 MPa is beneficial in order to have polymeric foam with small cell size. On the other hand, to achieve foams with higher cell density, 2 wt % of nanoclay, injection pressure of 140 MPa, and holding pressure of 110 MPa should be used.

Enhanced foaming ability of thermoplastic polyurethane by crystallization during mold-opening foam injection molding with supercritical N2 as blowing agents

Although the influence of hard segment content on the foaming behavior of thermoplastic polyurethane (TPU) has been reported in the literature, most of the studies have been limited to batch foaming, and the relationship between hardness on the foaming quality and the surface quality of TPU is still unclear in injection molding foaming. In this study, three hardnesses of TPU foams were prepared by core‐back injection foaming technique to investigate the relationship between hardness and TPU foaming behavior. Firstly, the relationship between hardness and viscosity of TPU was investigated using rotational rheometer. The results showed that the complex viscosity increased with the increase of hardness, especially the viscosity of high hardness TPU responded more significantly at low frequencies. In addition, a scanning electron microscope was used to analyze the cell morphology of TPU foams with different hardness. It was revealed that the cell morphology of 1098A foam with low hardness was deteriorated and deformed severely, with a cell size and cell density of 172.02 μm and 0.59 × 105 cells/cm3, respectively. With the increase of hardness, the cell morphology of high hardness 1071D foam was regular and rounded, its cell size decreased to 95.98 μm and cell density increased 4.43 × 105 cells/cm3. Surface roughness and mechanical experiments showed that the medium hardness 1065D foam had better surface quality and tensile toughness. The elongation at break of the TPU foams decreased with increasing hardness, while the high hardness 1071D foam had better tensile and flexural strength. This study provides understanding for the selection of a suitable hardness to prepare TPU foams with favorable foaming quality and corresponding mechanical properties.Highlights TPU foams of different hardness were prepared using core‐back chemical foaming injection molding technology. High hardness TPU foam had excellent tensile strength and flexural strength.

Solubility and diffusivity of CO2 and N2 in TPU and their effects on cell nucleation in batch foaming

Batch foaming of SAN/clay nanocomposites with scCO2: A very tunable way of controlling the cellular morphology

Poly(butylene adipate‐co‐terephthalate) (PBAT) has attracted considerable attention in the field of porous materials due to its excellent mechanical properties and biodegradability. However, PBAT foams often exhibit poor cell morphology as well as limited cell size and density during batch foaming, which severely restricts their practical applications. In this study, a synergistic modification strategy combining polymer blending and chain extension was proposed based on the mold‐opening microcellular injection molding (MOMIM) process. Under a target weight reduction of 15%, the effects of packing time and supercritical fluid (SCF) content on cell morphology and size distribution were systematically investigated. Meanwhile, poly(butylene succinate) (PBS) was incorporated into PBAT to enhance its crystallization behavior and regulate melt strength, while 1 wt% of chain extender ADR was introduced to improve interfacial compatibility and suppress foam shrinkage. The results demonstrated that when the PBS content reached 40 wt% with 1 wt% ADR, uniform PBAT microcellular foams with an average cell size below 3 μm and a cell density of 10 10 cells/cm 3 were successfully fabricated, representing a two‐order‐of‐magnitude increase in cell density compared with neat PBAT foam. In terms of mechanical performance, the modified foams exhibited a 196.3% increase in Young's modulus and a 77.5% improvement in tensile strength relative to pure PBAT foams. This work provides valuable insights for the industrial‐scale preparation of biodegradable PBAT‐based microcellular foams via injection molding.

The past decade has witnessed remarkable progress of the development and amelioration of thermoplastic polyether ester elastomer (TPEE), showing its promising wide-range utility. Herein we unraveled an unprecedented research to utilize β-cyclodextrin (β-CD) with perfect charring ability in TPEE in substitution of toxic halogen flame retardants. The TPEE/phosphorous–nitrogen flame retardants (P-N FR) (aluminum diethylphosphinate and melamine polyphosphate)/β-CD system was created and the flame retardance effects were determined using the limiting oxygen index (LOI) and the vertical burning test (UL94), while the charring effects of β-CD were measured by thermogravimetric analysis (TGA), laser Raman spectroscopy (LRS), and scanning electron microscopy (SEM). Besides, the mechanical properties and the morphology were tested by the universal testing machine and SEM. Results indicate that with 10 wt% of β-CD added to the TPEE/25 wt% P-N FR systems, the UL94 can reach to V-0 grade and the tensile strength of this blend was kept above 10 MPa, which can be applied in practice. To our delight, β-CD promoted the formation of stable and compact carbonaceous char, preventing the melt dripping and enhancing the properties and the charring mechanism was better studied by real-time Fourier transform infrared spectra. Being easy to construct, sustainable, and economic, the TPEE composite modified by β-CD and P-N FR is a reliable and widely applicable novel fire retardation material.

Polystyrene (PS) clay nanocomposites were synthesized and used to prepare foams in both batch and continuous extrusion process. It was found that the addition of a small amount of clay could greatly reduce cell size and increase cell density. Once exfoliated, the nanocomposite foam exhibits the highest cell density and the smallest cell size at the same particle concentration. Exfoliated microcellular nanocomposite foams with good surface quality was successfully produced using supercritical carbon dioxide.

Thermoplastic polyurethane (TPU) is one of the most widely used thermoplastic elastomers (TPE) due to its high strength and tear resistance, good elasticity, flexibility and damping properties. Enhancement of TPU properties can be achieved by either varying the hard-soft segment composition ratio or by the reinforcement with micro or nanoscale fillers. In the last decade, cellulose nanocrystals (CNC) have gained an increasing degree of interest from both academics and industries as ‘sustainable nanomaterials’, as they have high-axial mechanical properties and reinforcing capability, abundance, low density, renewability and biodegradability. Contemporary research activities centred on the reinforcement of TPU with CNC have typically employed solvent-based fabrication methods (solution/wet casting). For the successful translation of this new class of nanocomposite materials from laboratory research to widespread applications, processing via scalable approaches has to be demonstrated. The utility of CNC as TPU reinforcers has also been limited by the poor thermal stability of CNC, which are typically isolated via acid hydrolysis, as well as the poor quality of dispersion achieved when more scalable methodologies are used (eg. melt compounding). Thus, this study firstly aims to explore, optimise and develop CNC with enhanced thermal stability, and secondly, to incorporate these more thermostable CNC into high performance TPU nanocomposites via scalable melt-compounding and reactive extrusion methods. The research thesis is presented in three main parts. The first part is focused on the production/isolation of CNC with enhanced thermal stability and at a high production yield. CNC has been isolated via two methods, acid hydrolysis using mild acid and a scalable high energy bead milling process. Both processes have been optimised to isolate CNC with requisite thermal stability and dispersibility for TPU host polymers. The second part is focused on the processability of CNC into the TPU matrix via an intermediate-scale traditional twin screw extrusion melt compounding method. The third and final part is focused on the processing TPU/CNC nanocomposites via a large-scale reactive extrusion method, by pre-dispersing CNC in polyol and then performing in-situ polymerisation in a twin-screw extruder (i.e. reactive extrusion). The main outcomes or observations from this study are: • Isolation of CNC with enhanced thermal stability and dispersibility via mild acid hydrolysis, and with a higher production yield than the previously reported methods • Acid-free isolation of CNC with enhanced thermal stability at high production yields • Organic solvent-free processing of TPU/CNC nanocomposites • The performance of the host TPU matrix, a “workhorse” aromatic polyether grade, is remarkably enhanced by the incorporation strategies reported, without negatively affecting the important elastic properties and compliance of the TPU

The biodegradable nanocomposite foams can be developed using different fabrication techniques where the use of various kinds of bio-based nanofillers helps in tailoring the foam properties. A brief discussion on different techniques of fabrication, their economic viability, and industrial feasibility in regards to the polymeric foams is made in this chapter. Moreover, the available different biodegradable polymeric foams and their processing in the recent past years is detailed. However, the chapter mainly focuses on the biodegradable poly (lactic acid) (PLA)-based nanocomposite foams and their recent developments and breakthroughs. The addition of nanofillers for fabricating the foam greatly affects various foam properties such as cell size, cell density, and porosity. Other important properties such as thermal properties, mechanical properties, and wettability are also affected by the nanofiller materials. The degradation of PLA-based nanocomposite foams is greatly influenced due to the addition of various bio-based nanofiller materials. In this regard, the tailor-made properties of various biodegradable foams make them promising candidate in different areas of research.

Thermoplastic natural rubber (TPNR) is widely used across industries due to its unique blend of elasticity and processability. Thermoplastic vulcanizates (TPVs) based on thermoplastic polyurethane (TPU) offer excellent mechanical properties and flexibility, yet often require enhanced elasticity and durability. Blending TPU with natural rubber (NR) is promising; however, phase incompatibility reduces mechanical strength and thermal stability. To address this, epoxidized NR (ENR) was employed as a compatibilizer in TPU/NR blends. ENR’s hydrocarbon backbone interacts with crosslinked NR, while epoxy groups enhance adhesion with TPU. Incorporating 3 phr of ENR significantly improved crosslinking, increased tensile strength by 41.1%, enhanced stress relaxation, and lowered the glass transition temperatures of both TPU and NR phases in the TPU/NR blends. These effects are attributed to improved chemical bridging between TPU and NR. However, excess ENR disrupts phase compatibility, causing polymer entanglement and reduced strength. Optimizing ENR content is essential for developing high-performance TPU/NR blends. Printability was demonstrated using the material extrusion additive manufacturing (MEx-AM) fused deposition modeling (FDM), showing potential for flexible applications like splints and medical devices.

Corrugated thermoplastic polyurethane foams with high mechanical strength fabricated by integrating fused filament fabrication and microcellular foaming using supercritical CO2

Three-dimensional printing has already been shown to be beneficial to the fabrication of custom-fit and functional products in different industry sectors such as orthopaedics, implantology and dental technology. Especially in personal protective equipment and sportswear, three-dimensional printing offers opportunities to produce functional garments fitted to body contours by directly printing protective and (posture) supporting elements on textiles. In this article, different flexible thermoplastic elastomers, namely, thermoplastic polyurethanes and thermoplastic styrene block copolymers with a Shore hardness range of 67A–86A are tested as suitable printing materials by means of extrusion-based fused deposition modelling. For this, adhesion force, abrasion and wash resistance tests are conducted using various knitted and woven workwear and sportswear fabrics primarily made of cotton, polyester or aramid as textile substrates. Due to polar interactions between thermoplastic polyurethane and textile substrates, excellent adhesion and high fastness to washing is observed. While fused-deposition-modelling-printed polyether-based thermoplastic polyurethane polymers keep their abrasion–resistant properties, polyester-based thermoplastic polyurethanes are more prone to hydrolysis and can be partially degraded if presence of moisture cannot be excluded during polymer processing and printing. Thermoplastic styrene compounds generally exhibit lower adhesion and abrasion resistance, but these properties can be sufficient depending on the requirements of a particular application. Soft thermoplastic styrene filaments can be processed down to a Shore hardness of 70A resulting in three-dimensional printed parts with good quality and comfortable soft-touch surface. Finally, three demonstrator case studies are presented covering the entire process to realize the customized and three-dimensional printed textile. This encompasses product development and fabrication of a textile integrated custom-fit back protector and knee protector as well as customized functionalization of a technical interior textile for improved acoustic comfort. In the future, printing material modifications by compounding processes have to be taken into account for optimized functional performance.

Role of nano silica in supercritical CO2 foaming of thermoplastic poly(vinyl alcohol) and its effect on cell structure and mechanical properties

A flexible superhydrophobic thermoplastic polyurethane porous surface with good self-cleaning function prepared by supercritical CO2 foaming