TPU/PLA nanocomposites with improved mechanical and shape memory properties fabricated via phase morphology control and incorporation of multi-walled carbon nanotubes nanofillers

Shape memory polymer nanocomposites based on thermoplastic polyurethane (TPU)/polylactic acid (PLA) blends filled with pristine multi-walled carbon nanotubes (MWCNTs) and modified MWCNTs─COOH were fabricated by direct melt blending technique and investigated for its morphology, mechanical, thermal, electrical, and shape memory properties. Morphological characterizations by using transmission electron microscope (TEM) and field emission scanning electron microscope (FESEM) revealed better dispersion of MWCNTs─COOH in the polymer blend, which is attributed to the improved interfacial interactions between the polymer blends and MWCNTs-COOH. Loading of the MWCNTs-COOH in the TPU/PLA blends resulted in the significant improvements in the mechanical properties such as tensile strength and elastic modulus and these effects are more pronounced on increasing the MWCNTs─COOH loading amount, when compared to the pristine MWCNTs filled system. Thermal analysis showed that the glass transition temperature of the blends increases slightly with increasing loading of both pristine and modified MWCNTs in the system. The resistance of nanocomposites decreased from 2 × 10¹² Ω to 3.2 × 10¹⁰ Ω after adding 3% MWCNTs─COOH. The shape memory performance tests showed that the enhancement of shape recovery by 252% could be achieved at 3% MWCNTs loading, when compared to that of TPU/PLA blends.     

Annealing effect on the shape memory properties of polylactic acid (PLA)/thermoplastic polyurethane (TPU) bio-based blends

PLA and TPU were melt-blended to form shape memory bio-based blends with or without post-annealing effect. To the authors’ best knowledge, this is the first work to discuss the annealing effect on the PLA-based SMP blends. Annealed TPU showed regularly fractured surfaces unlike the macro-phase segregated domains for non-annealed TPU. After 3 h-annealing treatment, spherulites were observed for PLA, but not for TPU. The crystallinity of PLA increased, close to 3-fold increment, for annealed blends in comparison with non-annealed blends. The shape memory behaviors of PLA/TPU blends predeformed under three different predeformation temperatures (25, 80, 120 °C) were investigated. The annealing effect was helpful in enhancing the shape fixing ratio of the PLA/TPU (60/40) blend at high predeformation temperature of 120 °C in comparison with 25 °C. However, the suitable selection of the optimum predeformation temperature at 80 °C outweighed the annealing effect to attain the high shape fixing ratio, even in the case of non-annealed blends. The annealing effect often increased the perfection of crystal domains/interfaces and the larger crystal sizes, which would be detrimental to the molecular extensibility. The overall annealing effect on the shape recovery ratios were quite effective for both PLA/TPU blends of 80/20 and 60/40 without sacrificing the shape fixing ratios at the optimum predeformation temperature of 80 °C, attributing to the increased crystallinity of PLA and homogenized phase domains of TPU. Particularly, the annealing treatment did significantly increase the recovery ratio of the blends, more than 2-fold increment, especially for PLA/TPU (60/40) blend. At both lower or higher predeformation temperatures, the stress concentration between the increased crystalline domains and amorphous regions tended to dominate the annealing effect, leading to a negative contribution to the shape recovery processes.     

The morphology,properties, and shape memory behavior of polylactic acid/thermoplastic polyurethane blends

Biodegradable polylactic acid (PLA) was compounded with thermoplastic polyurethane (TPU) by twin‐screw extrusion at weight ratios of 90/10, 80/20, 70/30, and 60/40. The blends were investigated based on their phase morphology, thermal and mechanical properties, and shape memory properties. The tensile results showed that PLA was successfully toughened by TPU. When the TPU content was 40%, the elongation‐at‐break increased to 400%. The SEM morphology showed that TPU was dispersed uniformly in the PLA matrix; DMA and DSC results indicated that the two polymers were immiscible. Most interestingly, it was found that the blends exhibited a shape memory behavior and, unlike most of the existing shape memory polymers (SMPs), the PLA/TPU blends could be deformed at room temperature without an extra heating and cooling step. During the deformation process, TPU acted as a toughening agent that prevented the PLA/TPU blends from breaking; thus, the temporary shape could be kept and internal stress was stored in the blends. Upon heating to above the glass transition temperature of PLA (about 60°C), the deformed parts regained their original shapes quickly along with the release of the stress. POLYM. ENG. SCI., 55:70–80, 2015. © 2014 Society of Plastics Engineers     

Study on mechanical,thermal and shape memory properties of polycarbonate/thermoplastic polyurethane blends

The objective of the study is preparation of shape memory blend of polycarbonate (PC) and thermoplastic polyurethane (TPU). Polycarbonate is blended with three types of TPUs and subsequently mechanical, thermal, morphological, and shape memory properties of the PC/TPU blends are studied. When TPU content in the blend is higher than 40% (by weight), the glass transition temperature related to PC is not shown in the differential scanning calorimetry thermogram, indicating loss of PC properties. The 60/40 optimized blend of PC/TPUs exhibits maximum increment of about 1100% in elongation and 43% decrement in tensile strength. The shape recovery of the optimized blend obtained by addition of 40% (by weight) of TPUs in PC polymer is found to be 65% and shape fixity is 97%. These results suggest that the blend of PC/TPU may be utilized for various applications where shape memory property is required including strategic applications.     

Influence of blocked polyisocyanate on thermomechanical, shape memory and biodegradable properties of poly(lactic acid)/poly(ethylene glycol) blends

A series of shape memory biodegradable blends from poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were prepared by solution casting method. Ethyl cellosolve-blocked polyisocyanate (EC-bp) was synthesized and used as a cross-linker to obtain cross-linked PLA/PEG blends. The chemical structure of the prepared composite was confirmed by Fourier transform infrared spectra. Thermomechanical, thermal and shape memory properties of the blends were investigated and compared by dynamic mechanical analysis, thermogravimetric analysis and shape memory testing. The results showed that EC-bp cross-linked PLA/PEG blends had better thermal and thermomechanical properties than non-cross-linked blends and displayed good shape memory effects in both shape fixity rate and shape recovery rate. Moreover, the effect of EC-bp addition on the rate of biodegradable degradation in a phosphate buffer solution (pH 7.4) was studied at 37?°C. The prepared cross-linked PLA/PEG blends demonstrated better degradation resistance compared to the non-cross-linked blends.     

Effects of Blended Reversible Epoxy Domains on Structures and Properties of Self‐Healing/Shape‐Memory Thermoplastic Polyurethane

Few thermoplastic polyurethane (TPU) blending materials are reported to tune shape‐memory capability, self‐healing ability, and recyclability as well as mechanical property due to the different requirement of phase morphologies. This work focuses on how reversible epoxy domains affect the structures and properties of TPUs that contain disulfide bonds in main chains. The blended epoxy oligomers with dangling furan groups are miscible with the TPU. Self‐healing efficiency can be improved by such miscible epoxy oligomers that are also beneficial for shape recovery but harmful for shape fixation. In the presence of bis(4‐maleimidophenyl)methane (BMI), crosslinked epoxy domains phase separate from the TPU matrix to form microscale domains after the Diels–Alder (DA) reaction between furan groups and maleimide groups in BMI. Elastic modulus and tensile strength of TPU are greatly improved in comparison with pristine TPU and TPU/epoxy blends without BMI. The phase‐separated domains deteriorate the self‐healing, and the presence of phase‐separated microdomains facilitates the shape fixation but deteriorates the shape recovery. This work is not only useful to further understand the relation between structures of polymer blends with intelligent features, but also offers a useful approach to adjust the properties and capabilities of TPU in a cost‐effective manner.     

High-efficiency shape memory copolymers of polycaprolactone/thermoplastic polyurethane fabricated via in situ ring-opening polymerization

Shape memory blends of polycaprolactone/thermoplastic polyurethane (PCL/TPU) were prepared by in situ ring-opening polymerization (ROP) of ε-caprolactone (CL) and thermoplastic polyurethane (TPU). Fourier infrared spectrometer and ¹H-NMR were used to characterize the chemical structure of PCL/TPU copolymers. The results show that TPU has been involved in the ROP of CL, leading to the formation of copolymers with homogeneous morphologies. Besides, pure PCL and all the blends exhibit an excellent shape fixation ratio of 100%, due to their high crystallinity. When a small amount of TPU is introduced, the crystallinity of PCL decreases, and as a result, the shape recovery ratio of the copolymer is enhanced compared with pure PCL. However, with the increased loading of TPU, the content of PCL as the reversible phase decreases and the storage modulus of the PCL/TPU blend declines, so the driving force for the blends to return from the temporary shape to the initial shape becomes smaller, leading to a decrease in the shape recovery ratio. Notably, when the amount of TPU is only 5%, the shape recovery ratio of the blend could reach 83.3%, which is 26% higher than that of pure PCL, and meanwhile, the tensile strength of the blend decreases slightly. This study provides a new strategy for the design of shape-memory materials with high shape-memory properties.     

Influence of the morphology and viscoelasticity on the thermomechanical properties of poly(lactic acid)/thermoplastic polyurethane blends compatibilized with ethylene-ester copolymer

Viscoelastic, interfacial properties, and morphological data were employed to predict the thermal and mechanical properties of compatibilized poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blends. The combination of interfacial thickness measured by contact angle and entanglement density determined by dynamical mechanical analysis analyze data was employed to evaluate the mechanical behavior of PLA/TPU blends with and without ethylene-butyl acrylate-glycidyl methacrylate (EBG) compatibilization agent. The PLA/TPU blend (70/30 wt %) was prepared in a Haake internal mixer at 190 °C and compatibilized with different contents of EBG. The evaluation of the interfacial properties revealed an increase in the interfacial layer thickness of the PLA/TPU blend with EBG. The scanning electronic microscopy images showed a drastic reduction in the size of the dispersed phase by increasing the compatibilizer agent EBG content in the blend. The compatibilization of the PLA/TPU blends improved both the Izod impact strength and yield stress by 38 and 33%, respectively, in comparison with neat PLA/TPU blend. The addition of EBG into PLA/TPU blends significantly increased the entanglement density and the PLA toughening but resulted in a decrease of PLA deformation at break. The PLA and TPU glass transitions were affected by the EBG, suggesting that the PLA and TPU domains were partially miscible. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48926.     

TPU/PLA blend foams: Enhanced foamability,structural stability,and implications for shape memory foams

A series of thermoplastic polyurethane (TPU)/poly(lactic acid) (PLA) blends are studied in terms of morphological, thermal, and rheological properties by scanning electron microscopy, differential scanning calorimetry, and rheometry. Using supercritical CO₂ batch foaming, the foamability of the blends is systematically investigated. It is found that the 80/20 (wt %/wt %) TPU/PLA blend (TPU80%) shows vastly enhanced foamability over a wide range of foaming conditions to produce foams with a myriad of cellular morphology. The foamability enhancement results from the improved cell nucleation and growth, and the changes in the polymer microstructure. Compared to elastic TPU foams, the TPU80% retain their shapes 3.4 times better. Mechanism for the enhanced stability is proposed and verified using Kohlrausch–Williams–Watts model. The materials developed in the study and the mechanistic understanding of the shape fixation process may facilitate the advancement of elastomeric foams in conventional use as well as in novel shape memory applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47416.     

Preparation and Properties of Biodegradable Shape Memory Polylactic Acid/Poly(ε-caprolactone) Blends under Volume Elongational Deformation

In this work, a novel eccentric rotor mixer (ERM), which can generate circulating volume elongational deformation, is employed to prepare biodegradable polylactic acid (PLA)/poly(ε-caprolactone) (PCL) thermo-responsive shape-memory blends without a compatibilizer. The results of scanning electron microscopy (SEM) show that the ERM has more efficient dispersion and compatibilization for blends than conventional Banbury mixers, which is beneficial for shape-memory performance. The results of Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) also confirm the consequences. Then, morphological and mechanical properties and shape memory behaviors of the blends are investigated in detail. Co-continuous morphology is found on EF-PLA50. The blends exhibit remarkable shape-memory performance. The bending shape fixing ratio and recovery ratio of the blends are more than 94% and are still more than 90% after five shape memory cycles. With the increase of PLA content, the shape fixing ratio of blends decreases, while the shape recovery ratio increases and the shape recovery time becomes shorter. All the blends show good mechanical properties.     

异氰酸酯对聚乳酸/热塑性聚氨酯共混物性能的影响

以4,4^′-二苯基甲烷二异氰酸酯（MDI）为反应增容剂，采用熔融共混法制备了不同MDI含量的聚乳酸/热塑性聚氨酯（PLA/TPU）共混物，采用傅里叶变换红外光谱仪（FTIR）、万能试验机、冲击试验机、扫描电子显微镜（SEM）、差示扫描量热仪（DSC）和旋转流变仪对共混物力学性能、微观形态、热性能和流变性能进行了研究。结果表明：MDI可以有效改善共混物的力学性能，当MDI质量分数为1%时，共混物力学性能最佳，缺口冲击强度为40.0kJ/m²，断裂伸长率为214.1%，与未加MDI的共混物相比，分别增加了4.3倍和5.8倍，拉伸强度稍有下降（47.6MPa）；SEM表明，MDI的加入提高了共混物的相容性，加入MDI后，共混物的断面由海-岛结构变为核-壳包覆结构，相界面作用力增强；DSC测试表明，共混物的玻璃化转变温度、冷结晶温度和熔融温度随着MDI含量的增加而升高；流变测试表明，MDI质量分数的增加，共混物呈现更显著的剪切变稀行为，推测共混反应机理为：MDI质量分数的增加，体系内依次发生PLA的扩链、支化和TPU的交联。     

Multiple shape memory effects of trans‐1,4‐polyisoprene and low‐density polyethylene blends

A novel series of shape memory blends of trans‐1,4‐polyisoprene (TPI) and low‐density polyethylene (LDPE) were prepared using a simple physical blending method. The mechanical, thermal and shape memory properties of the blends were studied and schemes proposed to explain their dual and triple shape memory behaviors. It was found that the microstructures played an important role in the shape memory process. In TPI/LDPE blends, both the TPI crosslinking network and LDPE crystalline regions could work as fixed domains, while crystalline regions of LDPE or TPI could act as reversible domains. The shape memory behaviors were determined by the components of the fixed and reversible domains. When the blend ratio of TPI/LDPE was 50/50, the blends showed excellent dual and triple shape memory properties with both high shape fixity ratio and shape recovery ratio. © 2017 Society of Chemical Industry     

表面改性CNF对PBS/PLA共混物的湿热老化行为的影响

以硅烷偶联剂KH550对纳米纤维素(CNF)进行表面改性,利用双螺杆挤出机熔融共混制备一系列聚丁二酸丁二醇脂(PBS)/CNF母粒改性聚乳酸(PLA)复合材料,并在湿热老化试验箱中进行老化试验。通过扫描电子显微镜、广角X射线衍射仪、差示扫描量热仪、偏光显微镜等对复合材料的结晶和力学性能进行测试。结果表明,CNF可作为异相成核剂改善PLA的结晶行为,使PLA的结晶度提高;改性后,PBS/CNF复合母粒与PLA基体之间的相容性有较大改善;老化36 h后,PLA/PBS/CNF-KH550复合材料结晶进一步完善,其结晶度、拉伸强度和断裂伸长率较老化前分别提高了28.15 %、5.54 %和8.23 %。     

环氧聚合型扩链剂对POM/TPU共混体系的相容作用

使用环氧聚合型扩链剂作为POM/TPU共混物的相容剂,研究其对POM/TPU共混物的流变性能、力学性能、结晶性能和耐热性的影响。结果表明,添加环氧聚合型扩链剂后,POM/TPU共混物的熔体流动速率先升高然后降低;冲击强度提高,断裂伸长率大幅提高;结晶度先升高后降低;热变形温度提高。     

Thermo-responsive shape memory properties based on polylactic acid and styrene-butadiene-styrene block copolymer

This study aims to compare thermal, mechanical, and shape memory behavior of polylactic acid (PLA) blended with different structures of styrene-butadiene-styrene block copolymer (SBS), namely linear SBS (L-SBS), and radial SBS (R-SBS). The amount of L-SBS and R-SBS added was varied between 10 and 70 wt%, and the blending process was carried out using an internal mixer at 180°C before the shaping process by the compression molding. An improvement in the degree of crystallinity was observed across the entire composition range with less pronounced transition temperature change. Tensile strength and modulus of PLA/L-SBS blends were higher than PLA/R-SBS blends across all composition ranges. The results also revealed that the shape fixing ratio (R_f) and recovery ratio (R_r) of PLA/L-SBS were higher than PLA/R-SBS, with PLA70/SBS30 showed the best shape memory behavior. The morphology characteristics of the blend were also examined with the scanning electron microscope.     

Morphologies and mechanical properties of polylactide/thermoplastic polyurethane elastomer blends

To explore a potential method for improving the toughness of a polylactide (PLA), we used a thermoplastic polyurethane (TPU) elastomer with a high strength and toughness and biocompatibility to prepare PLA/TPU blends suitable for a wide range of applications of PLA as general‐purpose plastics. The structure and properties of the PLA/TPU blends were studied in terms of the mechanical and morphological properties. The results indicate that an obvious yield and neck formation was observed for the PLA/TPU blends; this indicated the transition of PLA from brittle fracture to ductile fracture. The elongation at break and notched impact strength for the PLA/20 wt %TPU blend reached 350% and 25 KJ/m², respectively, without an obvious drop in the tensile strength. The blends were partially miscible systems because of the hydrogen bonding between the molecules of PLA and TPU. Spherical particles of TPU dispersed homogeneously in the PLA matrix, and the fracture surface presented much roughness. With increasing TPU content, the blends exhibited increasing tough failure. The J‐integral value of the PLA/TPU blend was much higher than that of the neat PLA; this indicated that the toughened blends had increasing crack initiation resistance and crack propagation resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology and properties of shape memory thermoplastic polyurethane composites incorporating graphene‐montmorillonite hybrids

A novel hybrid containing graphene oxide (GO) and montmorillonite (MMT) was first synthesized by solution reaction. Then shape memory thermoplastic polyurethane (TPU) composites incorporating MMT–GO hybrid was fabricated via melt blending. Infrared spectra indicated that GO and MMT have been combined together through chemical hydrogen bonding. Tensile tests showed that MMT‐GO hybrids provided substantially greater mechanical property enhancement than using MMT or GO as filler alone. With only 0.25 wt % loading of MMT–GO hybrid (the mass ratio of MMT:GO is 1:1), there was a relatively high improvement in tensile properties of TPU composites, compared with those of TPU/GO and TPU/MMT composites at the same filler content. Thermal analysis indicated that MMT‐GO hybrids enhanced the thermal decomposition temperatures of TPU composites. Shape memory property tests showed that the shape fixing rate of TPU composites was effectively enhanced by incorporating MMT–GO hybrid. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46149.     

The influence of filler treatment on the properties of TPU/PP blends: I. Thermal properties and stability

Commercially available organosilane (3‐glycidoxypropyltrimethoxysilane (GPTMS)) coupling agent was used to treat talc in order to improve the affinity relative between the filler and the polymer in composites as well as filler and polymer in the thermoplastic polyurethane/polypropylene (TPU/PP) blends (talc content was 5 wt%). The talc particles were first modified with GPTMS and then introduced into TPU, PP as well as TPU/PP blends with different weight ratios of polymers using blending method and subsequently injection molded in a hydraulic press. The aim was to report the effect of silane coupling agent on the thermal and morphological properties of talc filled composites and blends. The results showed that the thermal properties of the TPU, PP composites and TPU/PP blends were improved with the addition of silane treated talc (higher melting (T_m), crystallization (T_c) temperatures and degree of crystallinity (χ_c)). The glass transition temperature (T_g) obtained by dynamic mechanical analysis (DMA) of the TPU soft segments in TPU/PP blends increased with the addition of untreated and silane treated talc due to lower mobility of the soft segments in TPU and better miscibility of TPU and PP. TPU/PP blends with the silane treated talc show better thermal stability than the TPU/PP blends with untreated talc. POLYM. ENG. SCI., 55:1920–1930, 2015. © 2014 Society of Plastics Engineers     

E-BA-GMA三嵌段共聚物对PLA/PBAT体系的增韧改性研究

研究了乙烯-丙烯酸正丁酯-甲基丙烯酸缩水甘油酯三嵌段共聚物(E-BA-GMA)作为增韧剂对聚乳酸(PLA)/对苯二甲酸、己二酸、1,4-丁二醇三元共聚酯(PBAT)共混物的力学性能、流动性能、热性能和断面形貌的影响。结果表明:E-BA-GMA的环氧官能团与PBAT/PLA体系的端羧基和端羟基发生反应,使得PBAT与PLA的相容性得到改善,共混物的冲击性能得到了明显的提高;E-BA-GMA的加入导致结晶温度向低温方向偏移和结晶度下降。     

The influence of heat treatment on the properties of shape memory fibers. II. Tensile properties,dimensional stability,recovery force relaxation,and thermomechanical cyclic properties

Shape memory fibers (SMFs) were prepared via a melt spinning process. The fibers were subject to different heat treatments to eliminate internal stress and structure deficiency caused during the melt spinning process. The influences of heat treatments on the SMF thermal properties, molecular orientation, tensile properties, dimensional stability, recovery force relaxation, and thermomechanical cyclic properties were studied. It was found that the heat treatments increased soft segment crystallinity and phase separation while decreased molecular orientation. The low‐temperature heat treatment increased the breaking elongation, shape fixity ratios, and decreased boiling water shrinkage while shape recovery ratios were decreased. High‐temperature treatment increased both the shape recovery ratios, fixity ratios, recovery stress stability and at the same time decreasing the fiber mechanical strength. The results from differential scanning calorimetry, molecular orientation apparatus, and cyclic tensile testing were used to illustrate the mechanism governing the mechanical properties and shape memory effect. To obtain comprehensive outstanding properties, the SMF is expected to be treated at a high temperature because of the hard segment high glass transition temperature. Unfortunately, the heat treatment could not be conducted at a too high temperature because the SMF became too tacky and soft due to the melting of the soft segment phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009