Pressure-induced Flow Processing Research Articles

In‐situ generation of biodegradable poly(lactic acid)/poly(butylene succinate) nanofibrillar composites via a facile and cost‐effective strategy of pressure‐induced flow processing

AbstractInspired by the fact that the in‐situ fibrillation structure can enhance the polymer's macroscopic mechanical performance, a facile and cost‐effective strategy based on the pressure‐induced flow (PIF) processing was developed to produce ultra‐strong and super‐tough biodegradable poly(lactic acid)/poly(butylene succinate) (PLA/PBS) blends. Under the action of external pressure field, the ductile and flexible PBS droplets deformed along the flow direction (FD) and shifted from spheroid to ellipsoid, eventually to nanofiber as the compression ratio (CR) increased. From the scanning electron microscopy (SEM) results, it was found that the PBS droplets did not in‐situ take shape into nanofibrils until the CR reached to 4, and the PBS nanofibrils served as the central shish to induce the PLA molecular chain to crystallize in the perpendicular direction, resulting in nanohybrid shish‐kebab superstructures. The Raman spectra and differential scanning calorimetry results confirmed the enhancement effect of the CR on the orientation degree, lamellar thickness, and crystallization properties. Benefiting from the abundant interlocked hybrid shish‐kebabs, the tensile strength, tensile modulus, and impact strength of the PIF processing PLA/PBS blend (CR = 4) reached the maximum value of 106.4 MPa, 2332.4 MPa, and 87.4 kJ/m2, respectively, which were 116.7%, 40.1%, and 20.8‐folds higher than those of the common PLA/PBS blend. Overall, it is believed that the proposed methodology put forward a facile and cost‐effective way to produce PLA‐based in‐situ fibrillation reinforced composites for engineering applications.

Pressure-induced flow processing behind the superior mechanical properties and heat-resistance performance of poly(butylene succinate)

Abstract We propose a pressure-induced flow (PIF) processing method for the simultaneous enhancement of strength, toughness, and heat resistance of biodegradable poly(butylene succinate) (PBS). The pressure and temperature were systematically adjusted to optimize the tensile strength of PBS. Under the optimized processing conditions, the structured PBS was characterized by relatively high strength of 89.5 MPa, toughness of 21.4 kJ·m−2, and improved heat resistance without deterioration of much of its ductility. Microscopic analyses witnessed denser and highly oriented crystalline domains along the flow direction caused by PIF processing. Detailed crystallization analysis made by 2D-WAXD and 2D-SAXS unraveled the extremely ordered PBS domains, which were featured by a significant increase in the orientation degree from 0.25 for the reference to 0.73 for PIF-processed PBS. Such a highly ordered microstructure substantially boosted the degree of crystallinity and heat-resistance temperature of PBS. We believe that our findings would offer a facile, green, and cost-effective approach for fabricating biodegradable polymers with outstanding properties and performance.

A facile strategy for preparation of strong tough poly(lactic acid) foam with a unique microfibrillated bimodal micro/nano cellular structure

This work reports the design and fabrication of strong tough poly(lactic acid) (PLA) foam by combining pressure-induced-flow (PIF) processing with supercritical CO2 foaming. PIF processing widened the foaming window of PLA to 40–120 °C, while supercritical CO2 foaming released the undesired internal stress of PLA samples with PIF processing (P-PLA). The prepared PLA foams displayed a unique microfibrillated bimodal micro/nano cellular structure which is strongly affected by saturation temperature (Ts). Both micron and nano cells showed decreasing cells size and increasing cell density as Ts elevated. The orientation factor as well as internal stress of PLA foams decreased with increased Ts. Compared with P-PLA samples, PLA foam prepared at Ts of 40 °C showed negligible reduction of orientation from 0.45 to 0.41 and release of internal stress characterized by the rightward shift of Raman peak (stretching vibration of CO bond from 1763 to 1766 cm−1). Furthermore, PLA foam prepared at Ts of 40 °C presented excellent impact strength (32.3 kJ/m2), tensile strength (42.0 MPa), and ductility (14.2%). The combination of PIF processing and supercritical CO2 foaming provides a facile and effective method to prepare strong tough PLA foam that has immense potential in biomedical, aerospace, automotive, and other structural applications.

High Impact Toughness ABS/CaCO<sub>3</sub> Nanocomposites Prepared through Pressure Induced Flow Moulding

ABS/CaCO3 nanocomposite with super toughness was processed by pressure induced flow (PIF) moulding. After PIF processing, the impact toughness of ABS/CaCO3 nanocomposite improved remarkably, the average highest Izod impact strength of nanocomposite increased to around 69 kJ/m2, which was 2.3 times higher than that of orignal ABS. Moreover, the relative toughening mechanism was investigated. The disk-like rubber domain and the cavities caused by calcium carbonate were researched by small angle X-ray scattering (SAXS). The synergy of them could prevent the craze becoming a large crack effectively.

Fabrication of high strength PA6/PP blends with pressure-induced-flow processing

Ultra high strength PA6/PP blend was fabricated with pressure-induced-flow (PIF) processing. It was found that the mechanical properties of PA6/PP blend with PIF processing were comprehensively and markedly higher than non-PIF PA6. Tensile strength increased by 290%, especially impact strength increased by 650%, even flexural strength was higher than non-PIF PA6 meanwhile. The morphology of PA6/PP blend samples was characterized by SEM and XRD, revealing that the blend with PIF processing has oriented structure both on macro-scale and micro-scale. Based on the relationship of structure and properties, the mechanism model of the significant enhancement was proposed. More crazes and voids were formed to consume the energy and also longer paths for dissipating energy were created inside the samples with PIF.

Toughening plastics by crack growth inhibition through unidirectionally deformed soft inclusions

We demonstrate that without changing the filler content mechanical properties of commodity plastics with immiscible soft inclusions can be decisively enhanced, simply by pressure induced flow processing in the solid state. As an example, we have chosen acrylonitrile-butadiene-styrene (ABS), where shape and orientation of the soft fillers were changed by processing, resulting in an array of aligned and oriented nanosize deformed rubber domains. These deformed domains effectively controlled the propagation of cracks inside the solid matrix and were responsible for a multifold increase of tensile and impact toughness. Thus, appropriate processing allows manufacturing plastics with high impact resistance in accordance with engineering needs.

Tough and strong polyamide 6,6 with oriented morphologies via pressure induced flow processing

Polyamide 6,6 (PA 6,6) is widely used as a key synthetic material. However, its applications are constrained by rather low toughness. The existing methods of toughening show limited improvements and sometimes may take the sacrifice of tensile strength. In this study, we proposed a novel way, named pressure induced flow (PIF) processing, to simultaneously boost the toughness and strength of PA 6,6. The toughness measured as impact strength increased by ∼340%, while the tensile strength increased by 164% at the same time. Scanning electron microscope observations revealed stratified morphologies in the PIF processed PA 6,6 with abundant oriented crazes and cavities, which are believed to be dominantly responsible for toughening and enhancement. Results in wide angle X-ray diffraction patterns suggested that Brill transition took place in PIF processing at a temperature higher than 160°C or under a pressure above 600 MPa. This led to an increase in resistance and reduction of ductility for the materials, resulting in a minor decline of toughness when processing temperature or pressure reached somewhat higher values (such as 160°C and 600 MPa). The PIF processing brought an orientation of (100) plane along flow direction, which might account for increase and orientation of crazes and cavities in the fractured surface of materials. In parallel to its advantages of energy saving, easy handling and easy controlling, PIF processing is expected to find broad industrial applications due to its unique effect on toughening and strengthening of semicrystalline polymer materials such as PA 6,6.

Study on biocompatible PLLA–PEG blends with high toughness and strength via pressure-induced-flow processing

In this paper, we report a novel and facile method of pressure-induced-flow (PIF) processing that remarkably enhanced the mechanical properties of polylactic acid (PLLA)–PEG blends. The impact strength and bending strength increased by about 20 and 4 times, respectively. Meanwhile, the tensile strength and elongation at break were 3 and 7 times higher compared with raw samples. As indicated by DSC and polarizing microscopy, POM, oriented spherulites were present in the sample after PIF processing. The SEM results showed that the fracture surface of the PIF samples became oriented and much rougher. The cell culture results indicated that the PLLA–PEG blends after PIF processing still maintain as good biocompatibility as the original.

Deformation and toughening mechanism for high impact polystyrene (HIPS) by pressure-induced-flow processing

In this paper, firstly, we systematically explain the deformation mechanism of the high impact polystyrene (HIPS) via pressure-induced-flow (PIF) processing. As indicated by TEM, AFM and SAXS, we find that a single salami domain is intensively deformed into a disk-like shape, and rubber-disk domains form parallel and oriented structure. In addition, chains in the interphase are oriented and become stiffer as suggested by FTIR and DMA. Such structural variation gives rise to the improvement in both strength and toughness. Impact and tensile strength for high impact polystyrene (HIPS) with parallel and oriented structure increase by 100% and 30% respectively. Moreover, we studied the toughening mechanism. The post-impact fracture surface transits from normal smooth fish scale like morphology to aligned grooves with high roughness, as demonstrated by SEM. The craze of impact fracture surface of HIPS samples after PIF processing is characterized by TEM. Finally, a model for the confinement of crazing is proposed.

Markedly improving mechanical properties for isotactic polypropylene with large-size spherulites by pressure-induced flow processing

Mechanical property of semicrystalline polymer with large-size spherulites is rather poor, and needs to be improved by adding nucleating agent to make spherulites smaller. However, the nucleating agent causes many problems limiting its applications. In this paper, we report a method to simultaneously improve the toughness and tensile strength of isotactic polypropylene (iPP) with large-size spherulites by deformation of spherulites and orientation of lamellaes through pressure-induced flow processing (PIF-processing) at solid state. The initial spherulite sizes of iPP samples with the same crystallinity and crystal form were controlled by adding nucleating agent (NA, Talc, nano-scaled), and then the samples were subjected to PIF-processing. The resulting mechanical performance of the bulk materials, including impact and tensile strength, was simultaneously enhanced. In particular, the impact strength increases upto 8 folds higher than those obtained by conventional processing for the same bulk materials, attributing to the synergistic effect of both the orientation and the large-size spherulites. The measurements of SEM, XRD and SAXS revealed the spherulites deformation and lamellae orientation during PIF-processing, as the basis of discussing the mechanism.

The Thermal and Mechanical Properties of Ultra-High Molecular Polyethylene/Montmorillonite Clay (UHMWPE/MMT) Nanocomposites Using Gel and Pressure-Induced Flow Process (PIF)

This paper examines hybrid organic-inorganic polymer nanocomposites incorporating organically modified montmorillonite (MMT) and ultra-high molecular weight polyethylene (UHMWPE). UHMWPE/MMT hybrid nanocomposites were prepared using gel and pressure-induced flow (PIF) processing methods at a gel concentration of 8 wt.% UHMWPE with various organoclay contents (0, 5, 10, 15, and 20 pphr). The interlayer properties of the nanocomposites were studied by X-ray diffraction (XRD) transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The thermal and mechanical interfacial properties of the nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and the use of a universal test machine (UTM). XRD and TWM indicated that the nanocomposites were formed upon dispersion of MMT in the polymer matrix. From the DSC, TGA and DMA results, we found that the thermal stability of the UHMWPE nanocomposites increased as the MMT content increased. The nanocomposites showed higher tensile strengths than those of pure UHMWPE gel sheet. These findings indicate that the interfacial and mechanical properties were improved by the addition of MMT and PIF processing.

The Effect of Pressure-Induced Flow Processing on the Tensile Properties and Crystal Structure of Polypropylene

Mechanical properties have close relation with microstructure. Based on orientation of the molecule chain in fiber, they show a rapid increase in tensile properties. Nevertheless, block materials mainly gain rise of mechanical properties by blend or composite, it is hardly proposed on the self-reinforced materials by optimizing the microstructure. In this work, the structure and tensile properties of polypropylene (PP), treated at 105°C for 5min under different pressure, were studied with microscopy, differential scanning calorimetry (DSC). The variety of supra-structure that the spherulite deforms into ellipse even fractures piece in the pressure field adds to the mechanical properties. The orderliness of crystal increases with the pressure, and Tm is increased slightly from the original level.