苯磷酸锌改性聚L-乳酸的非等温结晶和热稳定性

利用苯磷酸锌(ZP)对聚L-乳酸(PLLA)基体改性,借助差示扫描量热仪(DSC)、X射线衍射仪(XRD)以及热失重分析仪(TGA)等研究ZP对PLLA非等温结晶行为和热稳定性的影响。结果表明:ZP作为异相成核剂可加速PLLA的结晶,且随着ZP含量的增加,结晶可在更高温度下发生。ZP的加入对PLLA的热失重曲线趋势影响不大,但起始分解温度会下降,从而降低PLLA的热稳定性。而对PLLA/ZP体系而言,其热稳定性对ZP含量的依赖性较小。     

辛二酸二苯甲酰肼对聚乳酸结晶的影响

采用差示扫描量热仪(DSC)、偏光显微镜(POM)、流变仪等多种测试方法，研究了有机成核剂辛二酸二苯甲酰肼(BOAD)在聚L-乳酸(PLLA)非等温结晶过程中的作用。研究表明，BOAD是一种高效的PLLA成核剂，能大幅提高PLLA的结晶速率。BOAD在PLLA基体中具有一定溶解性，在熔融共混时溶解进入PLLA熔体，温度降低后，从PLLA基体中析出结晶，为PLLA提供异相晶核。从PLLA中析出的BOAD的晶体形貌与其添加量有关，并且可对BOAD的成核效果产生显著影响。当BOAD含量为0.75%时，从PLLA中析出的BOAD晶体呈树枝状，PLLA在其表面附生结晶，并且与其形成特殊的“枝叶结构”。在该情况下，BOAD的成核效果最佳，PLLA的结晶峰温度最高。     

环己烷羧酸盐成核剂改性PLLA的非等温结晶行为研究

采用差示扫描量热(DSC)法考察了环己烷羧酸盐成核剂N-20的引入对左旋聚乳酸(PLLA)非等温结晶行为的影响,然后通过Jeziorny法、Ozawa法和莫志深法对改性PLLA材料的非等温结晶动力学进行了分析。结果表明:N-20的引入使PLLA的结晶能力得到显著提升,其中,N-20添加量为1.0%的改性PLLA试样的结晶性能优于添加量为0.4%的试样;N-20添加量的增加并未改变PLLA晶体的生长模式,但加快了结晶速率。此外,Jeziorny法、Ozawa法和莫志深法三种分析方法中,仅莫志深法适合于描述改性PLLA材料的非等温结晶过程,其分析结果与DSC测试结果相一致。     

芳香族水杨酰肼衍生物对PLLA热性能的影响

采用酰化和氨化反应合成了3种不同结构的芳香族水杨酰肼衍生物,考察其对聚乳酸(PLLA)非等温结晶行为、熔融行为和热稳定性的影响。结果显示:随着芳香族水杨酰肼衍生物中酰胺基团数目的增加,其改性PLLA材料的非等温结晶峰向高温方向移动,且结晶峰也更加尖锐,表明酰胺结构有利于促进PLLA的结晶;与芳香族水杨酰肼衍生物相比,改性PLLA材料等温结晶后的熔融行为受结晶温度的影响更大;热稳定性测试显示芳香族水杨酰肼衍生物的加入会降低PLLA的起始分解温度,但不会改变PLLA的热分解趋势。     

成核剂TMC-306对聚乳酸结晶及力学性能的影响

针对聚乳酸结晶速率慢和冲击强度低的问题,采用添加成核剂TMC-306与L-聚乳酸(PLLA)熔融共混,利用差示扫描量热仪(DSC)、X射线衍射仪(WAXD)、偏光显微镜(POM)等测试手段考察了成核剂TMC-306对PLLA结晶和性能的影响。结果表明,添加TMC-306的PLLA在降温过程中出现了明显的结晶峰;等温结晶分析表明TMC-306的加入缩短了PLLA结晶时间、结晶速率加快,且结晶速率随着温度的升高而加快。另外,PLLA的成核密度增加、球晶尺寸减小,但对PLLA晶型没有影响。同时,成核剂TMC-306的添加使得PLLA的拉伸强度和弯曲强度降低,而耐热性和缺口冲击强度得以改善,在TMC-306含量为0.4%时,PLLA的冲击强度提高了2.7倍。     

聚乳酸/聚乙二醇共混物的结晶与降解行为

针对聚乳酸（PLLA）亲水性差、降解周期长的问题,利用与亲水性高分子聚乙二醇（PEG）共混的方法对其进行改性。采用转矩流变仪制备了不同组成的PLLA/PEG共混物颗粒,系统研究了PLLA/PEG共混物的结晶和熔融、亲水性和在酸碱介质中的降解行为。结果表明,PEG的加入增强了共混物中PLLA的结晶能力,提高了PLLA在降温过程中的熔融结晶温度。PLLA/PEG共混物在等温结晶中表现出比纯PLLA更快的结晶速度。通过改变PLLA/PEG共混物的组成,可调控材料的表面亲水性和降解速率。随着PEG含量的增多,PLLA/PEG共混物的表面接触角降低。PLLA与PLLA/PEG共混物均可在水溶液中降解,共混物的降解速率高于纯PLLA,随着PEG含量的升高和降解液中酸碱浓度的提高,PLLA/PEG共混物的降解速率加快。     

加工条件对聚L-乳酸热性能的影响

为了更好地掌握聚L-乳酸(PLLA)的加工工艺,系统考察了PLLA熔融温度和时间对其热性能的影响。结果表明:增加熔融时间会使PLLA非等温结晶峰变得尖锐,熔融40 min后PLLA的非等温结晶峰最为显著,而熔融时间的增加会使等温结晶后的熔融过程呈现出熔融双峰现象;熔融温度的增加则会使PLLA非等温结晶峰变得更加尖锐。     

聚羟基丁酸己酸酯对聚乳酸结晶性能的影响

通过溶液共混法制备了生物可降解左旋聚乳酸(PLLA)和聚羟基丁酸己酸酯(PHBHHx)复合材料,用差示扫描量热仪和偏光显微镜研究了PHBHHx对PLLA热性能与结晶性能的影响。结果表明,PLLA与PHBHHx存在一定的相容性和相互作用,PLLA的玻璃化转变和冷结晶行为随着共混组成而变化。PLLA的相对分子质量越大,球晶形貌的规整性越差。当PHBHHx含量达到30%(质量分数,下同)时,其能加快PLLA的链段运动,提高结晶的成核密度,加快结晶速率。     

不同构型聚乳酸共混体系的立构复合结晶研究进展

左旋聚乳酸(PLLA)和右旋聚乳酸(PDLA)在共混体系中可形成立构复合(sc)结晶,与聚乳酸(PLA)同质结晶材料相比,sc 结晶材料具有良好的耐热性和耐化学稳定性。因此,sc 结晶是改善PLA 综合性能的一种有效手段。但在PLLA/PDLA 共混体系中,存在各自的同质结晶与两者之间sc 结晶的竞争,所以制备高耐热sc 型PLA 材料的关键之一是理解其sc 结晶的形成条件与机理,进而调控和促进其sc 结晶程度。在PLLA/PDLA 共混物中,sc 结晶受聚合物化学结构、结晶与加工条件等诸多因素影响,其影响规律和机理较复杂。根据PLLA/PDLA共混物sc 结晶行为影响因素的不同,从聚合物分子量、立构规整性、共混比例、分子链拓扑结构、结晶方式与条件、加工助剂和其他组分加入6 个方面出发,详细综述了PLLA/PDLA 共混物sc 结晶及其sc 材料制备的研究进展,以期为高耐热生物基PLA 材料的加工制备提供指导。     

聚L-乳酸的热性能研究

为了了解聚L-乳酸(PLLA)自身结构特点,更好地控制其成型加工过程,研究了PLLA的非等温结晶行为、熔融行为和热失重过程。结果表明:降温速率对PLLA的非等温结晶过程具有显著影响,在1℃/min的降温速率下,PLLA的结晶起始温度为121℃,结晶焓为3.363 J/g;PLLA的熔融双峰遵循熔融-再结晶的机理;PLLA热分解温度在300℃左右,且随升温速率的增加而增大。     

The relationship between solubility and nucleating effect of organic nucleating agent in poly(L-lactic acid)

N,N′-bis(benzoyl) hexanedioic acid dihydrazide (BHAD), and N,N′-bis(benzoyl) terephthalic acid dihydrazide (BTAD) were synthesized as the organic nucleating agents for poly(L-lactic acid) (PLLA). These two organic compounds exhibited different nucleating effect to PLLA. When the concentration was very low, BTAD was able to nucleate PLLA, while BHAD was not. When the concentration was adequate, BHAD showed better nucleating effect than BTAD. The experiments showed that, BHAD had the ability of dissolving into PLLA melt matrix, while BTAD was insoluble in PLLA. The optical microscope images revealed the quite different PLLA crystal morphologies nucleated by BHAD and BTAD. As BTAD could not dissolve in PLLA melt, it only induced a mass of small grain crystals of PLLA, the morphology of which is the same as neat PLLA. BHAD had relatively different nucleation and crystallization behaviors. Upon heating, BHAD could partially or totally dissolve in PLLA melt, which depended on the final heating temperature and its concentration. Upon cooling, BHAD separated from PLLA matrix and formed needle like or dendritic structures. Moreover, totally dissolved BHAD could finally exhibit dendritic structures, which had an excellent nucleation effect to PLLA. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46851.     

Poly(l‐lactic acid) with the organic nucleating agent N,N,N′‐tris(1H‐benzotriazole) trimesinic acid acethydrazide: Crystallization and melting behavior

N,N,N′‐Tris(1H‐benzotriazole) trimesinic acid acethydrazide (BD) was synthesized from 1H‐benzotriazole acetohydrazide and trischloride to serve as an organic nucleating agent for the crystallization of poly(l ‐lactic acid) (PLLA). First, the thermogravimetric analysis of BD exhibited a high thermal decomposition temperature; this indicated that BD maybe used as a heterogeneous nucleating agent of PLLA. Then, the effect of BD on the crystallization and melting behavior of PLLA was investigated through differential scanning calorimetry, depolarized light intensity measurements, and wide‐angle X‐ray diffraction. The appearance of a nonisothermal crystallization peak and increases in the glass‐transition temperature and the intensity of the diffraction peak suggested that the presence of BD accelerated the overall PLLA crystallization. Upon cooling at a rate of 1°C/min, the addition of just 0.5 wt % BD to PLLA increased the onset crystallization temperature from 101.4 to 111.3°C, and the nonisothermal crystallization enthalpy increased from 0.1 to 38.6 J/g. The isothermal crystallization behavior showed that the crystallization half‐time of PLLA with 0.5 wt % BD (PLLA/0.5% BD) decreased from 49.9 to 1.1 min at 105°C. However, the equilibrium melting point of PLLA/0.5% BD was lower than that of the pristine PLLA; this resulted from the increasing nucleating density of PLLA. The melting behavior of PLLA/0.5% BD further confirmed that BD improved the crystallization of PLLA, and the double‐melting peaks of PLLA/0.5% BD were assigned to melting–recrystallization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42402.     

Low-molecular weight aliphatic amides as nucleating agents for poly (L-lactic acid): Conformation variation induced crystallization enhancement

Two kinds of low molecular weight aliphatic amides, N, N′-ethylenebis (12-hydroxystearamide) (EBH) and N, N′-ethylenebisstearamide (EBSA), have been selected in present study to mediate the crystallization behavior of poly (L-lactic acid) (PLLA). The results showed that the crystallization rate of PLLA was significantly improved with the addition of EBH and EBSA, and EBH presented a stronger nucleating efficiency. The correlation between the variation of chain conformation during the early stages of isothermal crystallization and the enhancement of crystallization rate for pure PLLA and its mixtures was investigated by time-resolved FTIR. The formation of interchain conformational-ordered structure and intrachain 10₃ helix structure for amide-doped PLLA preceded that for pure PLLA, suggesting a stimulatory nucleating effect of EBH and EBSA. In the case of PLLA/EBH, the interchain interactions of –(COC + CH₃) and –CH₃ groups were faster than the –(CH₃+CC) intrachain interactions, while the interchain interactions and the intrachain 10₃ helix formation were nearly synchronous for PLLA/EBSA. The hydrogen bond interaction between hydroxyl groups in EBH and the carbonyl groups in PLLA was proposed to be an important factor influencing the conformation variation during isothermal crystallization of PLLA.     

Unique Crystallization Behavior of Poly(L-lactic acid) Nucleated by Stereocomplex with Different Fine Structure

Effect of the addition of poly(D-lactic acid) (PDLA) as stereocomplex (SC) on crystallization behavior of poly(L-lactic acid) (PLLA) had been systemically investigated. The result indicated that the inclusion of PDLA with higher MW into PLLA exhibited lower t _1/2 and showed accelerated crystallization behavior. Meanwhile, SC formed in blends with higher MW of PDLA exhibited enhanced nucleation activity. In combination with both DSC and WAXD analysis, it was believed that nucleation process was more related to the crystalline size of SC. The result in this study would provide guidance for the application of SC as nucleating agent for the PLA-based products.     

一种新型成核剂对聚乳酸等温结晶行为的影响(英文)

The effect of a novel active nucleating agent(TBC8-eb) on the isothermal crystallization of poly(L-lactic acid) (PLLA) was studied by differential scanning calorimetry(DSC) and Fourier transform infrared spectroscopy(FTIR) . The analysis on kinetics demonstrates that TBC8-eb can not only accelerate the crystallization rate but also transform most of the original spherulite crystals of PLLA into sheaf-like crystals. Furthermore,the free energy of folding(σe) of PLLA and PLLA with TBC8-eb is 0.15 and 0.06 J·m-2,respectively,which suggests that the addition of TBC8-eb favors the regular folding of molecule chains in the crystallization of PLLA,improv-ing its crystallization rate. The FTIR results show that TBC8-eb can accelerate the conformational ordering of PLLA in the isothermal crystallization. The conformational ordering of PLLA nucleated with TBC8-eb begins with the interchain interaction of CH3,and then a short helix emerges where a couple of CH3 groups interact.     

对叔丁基杯[4]芳烃包合物对聚乳酸结晶过程的影响

以对叔丁基杯[4]芳烃(tBC4)为主体,甲苯、邻二甲苯、间二甲苯、对二甲苯为客体分子,制备4种tBC4包合物tBC4-t、tBC4-ox、tBC4-mx、tBC4-px。考察了tBC4包合物对左旋聚乳酸(PLLA)结晶性能及结晶形态的影响。结果表明,tBC4包合物能将PLLA的结晶峰值温度(T_p)提高近7℃;进一步研究发现几种包合物在经高温后,客体小分子逃逸,样品均改变为相同的晶体结构,因此对PLLA成核有相同的影响;此外,含有成核剂的PLLA球晶尺寸小于空白PLLA的球晶尺寸,成核剂的加入不改变PLLA球晶生长的方式。     

苯基磷酸锌对聚乳酸结晶行为影响的研究

采用DSC,POM研究了成核剂苯基磷酸锌（PPZn）对聚乳酸结晶行为的影响。结果表明：PPZn可以作为聚乳酸的高效成核剂,PPZn的加入显著提高了聚乳酸的结晶速率和结晶度。当PPZn的质量分数为5％0时TCs（起始结晶温度）降低了约24℃,TCe（终止结晶温度）降低了约29℃。PPZn的加入使聚乳酸的半结晶时间大大缩短。当PPZn的质量分数为2％时,结晶速率常数增大约5个数量级。     

Crystallization behavior and crystallite morphology control of poly(L‐lactic acid) through N,N′‐bis(benzoyl)sebacic acid dihydrazide

Adding a nucleating agent is one of the best ways to accelerate the crystallization rate of poly(L ‐lactic acid) (PLLA) so as to obtain a high degree of crystallinity during the process, which will improve the heat distortion temperature of final products. In the work reported, N, N′‐bis(benzoyl)sebacic acid dihydrazide (BSAD) was synthesized and used as a nucleating agent for PLLA. Isothermal and non‐isothermal crystallization behaviors were investigated using differential scanning calorimetry (DSC). The addition of BSAD successfully enhances the crystallization rate of PLLA. A unique phase separation behavior of PLLA/BSAD blends is found from DSC as well as from polarized optical microscopy, which explains the difference of optimal BSAD concentration between isothermal and non‐isothermal crystallization. This is the first recording of a phase separation peak in PLLA/nucleating agent blends using DSC. In thermogravimetric analysis, the enhanced thermal stability indicates that there are strong hydrogen bonds between BSAD and PLLA matrix. BSAD can dissolve in PLLA melt below its melting point through intermolecular hydrogen bonding with PLLA and self‐assemble upon cooling, leading to the surface being capable of nucleating PLLA. Different phase separation temperatures can be used to control the morphology of BSAD, which finally determines the crystallite morphology of PLLA. © 2012 Society of Chemical Industry     

Rapid crystallization of poly(l-lactic acid) induced by a nanoscaled zinc citrate complex as nucleating agent

A nanoscaled zinc citrate complex (ZnCC) was synthesized by the reaction of zinc acetate and citric acid using solution method. As a new eco-friendly nucleating agent, ZnCC was introduced into poly(l-lactic acid) (PLLA) via melt blending. The nonisothermal and isothermal crystallization, melting behavior, crystalline morphology and mechanical properties of the PLLA/ZnCC blends were investigated. It is found that ZnCC exhibits much more prominent nucleation activity on the crystallization of PLLA than conventional nucleating agent talc and commercial zinc citrate (ZnCit). By loading 0.05 wt% ZnCC, PLLA can complete crystallization upon cooling at 10 °C/min, and the crystallization peak shifts to a higher temperature with increasing ZnCC content. In the case of isothermal crystallization from the melt, the addition of ZnCC leads to a shorter crystallization time and a faster overall crystallization rate. Besides, the nucleation density of PLLA increases and the spherulite size decreases significantly in the presence of ZnCC. Epitaxy is the possible mechanism to elucidate the nucleation phenomenon of PLLA/ZnCC system. The tensile results show that ZnCC has a plasticization effect on the amorphous PLLA. Through a short-time annealing procedure, the mechanical properties such as tensile modulus and storage modulus of PLLA are improved by the addition of ZnCC.     

The nucleation effect of N,N′-bis(benzoyl) alkyl diacid dihydrazides on crystallization of biodegradable poly(l-lactic acid)

Five N,N??-bis(benzoyl) alkyl diacid dihydrazides were synthesized from benzoyl hydrazine and alkyl diacyl dichloride which were derived from alkyl diacid via acylation. PLLA/N,N??-bis(benzoyl) alkyl diacid dihydrazide samples were prepared by melt blending and hot-press forming process. The nucleation effect of N,N??-bis(benzoyl) alkyl diacid dihydrazide on crystallization of biodegradable poly(l-lactic acid) (PLLA) was investigated using differential scanning calorimetry (DSC) and vicat softening analysis. The results showed that five N,N??-bis(benzoyl) alkyl diacid dihydrazides acted as powerful nucleating agent for PLLA; with incorporation of N,N??-bis(benzoyl) alkyl diacid dihydrazide, the crystallization peak became sharper and shifted to higher temperature as the degree of supercooling decreased at a cooling rate of 1?°C/min from melt. The nucleation activities of five N,N??-bis(benzoyl) alkyl diacid dihydrazides were quantitatively determined. It is shown that N,N??-bis(benzoyl) suberic acid dihydrazide has higher nucleating activity than the other N,N??-bis(benzoyl) alkyl diacid dihydrazides. In the presence of N,N??-bis(benzoyl) alkyl diacid dihydrazide, the melting behavior of PLLA is affected significantly. In addition, the thermal stability of PLLA/0.8?% N,N??-bis(benzoyl) alkyl diacid dihydrazide is tested and reported. Compared to the neat PLLA, the onset degradation temperature of PLLA/0.8?% N,N??-bis(benzoyl) alkyl diacid dihydrazide samples has been decreased significantly.