SiO2/聚（3-羟基丁酸酯-co-4-羟基丁酸酯）薄膜研究

目的研究纳米SiO2对可生物降解聚(3-羟基丁酸酯-co-4-羟基丁酸酯)(P34HB)包装膜结晶行为和力学性能的影响。方法采用溶液浇铸法制备SiO_2/P34HB纳米复合薄膜,利用红外光谱仪(FTIR)、扫描电镜(SEM)、正置热台显微镜(POM)、差示扫描量热仪(DSC)和万能力学试验机等研究纳米SiO_2对P34HB结构、结晶性和力学性能等的影响。结果纳米SiO_2在P34HB中起到异相成核的作用,SiO2/P34HB复合膜的结晶速率和结晶度得到明显改善。相比P34HB包装膜,当纳米SiO_2质量分数为2%时,SiO_2/P34HB复合膜的弹性模量和拉伸强度分别提高了72.7%和60.9%。结论获得了纳米SiO2改善可生物降解聚(3-羟基丁酸酯-co-4-羟基丁酸酯)包装膜结晶度和力学性能的最佳掺杂比例参数。     

聚(3-羟基丁酸-co-4-羟基丁酸酯)/碳纳米管复合微孔发泡薄膜研究

用红外(FT-IR)谱、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和差示扫描量热仪(DSC),研究了多壁碳纳米管(MWCNT)分别在强酸和偶氮二异丁腈(AIBN)+过氧化二苯甲酰物(BPO)中的表面修饰过程,并将其与聚(3-羟基丁酸-co-4-羟基丁酸酯)/碳纳米管复合,制备了微孔发泡薄膜,孔径最大50μm,最小10μm。结果表明,在相同溶剂条件下,偶氮二异丁腈+过氧化二苯甲酰可以成功地实现碳纳米管的表面修饰,修饰后的碳管浓度为1%(质量分数)与聚合物较好相容,当其比例为1∶2、1∶1时分别获得"莲蓬型"和"蜂窝型"微孔发泡结构薄膜,并具有较好的导电性。     

4-羟基丁酸含量对聚 3-羟基丁酸 与 4-羟基丁酸共聚物性能和结构的影响

目的对3-羟基丁酸4-羟基丁酸共聚酯P(3HB-co-4HB)进行酶解测试。方法通过力学性能测试、失重率分析、热失重分析、X-射线衍射分析、扫描电镜等测试和表征手段对样品的物理性能及生物降解情况进行评价。结果 P(3HB-co-4HB)分子中4HB单体(文中均用摩尔分数表示)的引入提高了材料的柔韧性,材料的脆性下降;失重率方面,4种材料的降解速率从高到低依次为P(3HB)P(3HB-co-5%4HB)(3HB-co-10%4HB)P(3HB-co-15%4HB);酶解前期,材料的热稳定性增强,而酶解后期材料的热稳定性逐渐下降;XRD结果表明材料降解过程中结晶度的变化不明显;P(3HB-co-4HB)分子中随着4HB单体含量的增加,材料表面粗糙度降低,酶解后材料表面被侵蚀,降解速率与失重率结果一致。结论 P(3HB-co-4HB)分子中4HB单体的引入显著影响了材料的机械性能,随着4HB含量的增加,材料的失重率越来越大,热稳定性呈现先上升后下降的趋势,材料表面粗糙度逐渐降低,由于酶解过程属于从表面侵蚀开始,因此酶解过程中样品的结晶度变化不大。     

聚氧化乙烯(PEO)及其与高氯酸锂复合体系的等温结晶动力学研究

用示差扫描量热法研究了PEO及其与高氯酸锂复合体系的等温结晶过程。用Avrami方程分析了PEO和复合体系中PEO的等温结晶动力学,得到了PEO在不同体系中等温结晶时的动力学参数。PEO的Avrami指数n都趋近2．5,说明PEO晶体以三维方式依热成核生长。动力学参数表明,复合体系中PEO结晶时以异相成核为主。LiClO4对PEO等温结晶过程的影响如下：作为PEO结晶的成核剂而加快其结晶过程;增加了复合体系的粘度,缩短了PEO的结晶半时间,使其结晶总速率增大;降低了复合体系中PEO的绝对结晶度。     

Thermal degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) in nitrogen and oxygen studied by thermogravimetric-Fourier transform infrared spectroscopy

The thermal degradation behavior of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx), HHx=12 mol%) has been studied under different environmental conditions by thermogravimetric analysis (TGA) Fourier transform infrared (FT-IR) spectroscopy. It is reported that at higher temperature (>400 degrees C) carbon dioxide and propene are formed from the decomposition product crotonic acid in a nitrogen atmosphere, whereas in an oxygen atmosphere propene oxidizes in a further step to carbon dioxide, carbon monoxide and hydrogen. It was also found that PHB and P(HB-co-HHx) have a similar thermal degradation mechanism. The analysis of the FT-IR-spectroscopic data was performed with 2D and perturbation-correlation moving-window 2D (PCMW2D) correlation spectroscopy.     

Co-crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

A combined study of X-ray diffraction, differential scanning calorimetry and density measurements in copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate is presented. It is shown that the unit cell volume expands linearly with the comonomer content in the polymer. The reduction in the enthalpy of fusion is interpreted in terms of limited co-crystallization of the two monomers. The amount of 3-hydroxyvalerate in the crystals has been estimated to be approximately equal to two-thirds of the total content in the copolymer.     

Anti-inflammatory prodrugs as plasticizers for biodegradable implant materials based on poly(3-hydroxybutyrate)

Salicylic and acetylsalicylic acid esters were tested as plasticizers for biodegradable poly(3-hydroxybutyrate) (PHB). The aim is the combination of plasticizing and anti-inflammatory properties in the fabrication of implant materials. Solution-cast films made of mixtures of PHB and 30% ester showed plasticization accompanied by a decrease of elastic modulus and an increase in elongation at break in comparison with pure PHB films. However, the number of usable plasticizers from the group of the salicylic acid and acetylsalicylic acid esters is limited. Short-chain derivatives are volatile while long-chain compounds tend to crystallize. In both cases PHB films embrittle within short time. Moreover, some derivatives show a fast release in an aqueous environment. As alternative nonsteroidal anti-inflammatory prodrugs arylpropionic acid esters were tested as plasticizers. The addition of ketoprofen ethyl ester led to PHB films with decreased brittleness. In summary, various esters of anti-inflammatory drugs show plasticizing effects on solution-cast PHB films comparable with those of commonly used citric acid esters.     

聚丁二酸丁二酯/聚(3-羟基丁酸酯-co-4-羟基丁酸酯)/纳米高岭土熔融共混力学性能、流变及降解行为研究

用熔融共混挤出法制备的聚丁二酸丁二酯(PBS)/聚(3-羟基丁酸酯-co-4-羟基丁酸酯)[poly(3HB-co-4HB)]/纳米高岭土(nano Kaolin)复合降解材料;利用万能拉力机、旋转流变仪和SEM对其力学性能、流变行为、微观结构及降解性能进行研究。结果表明,PBS/poly(3HB-co-4HB)/nano Kaolin(100/10/8)复合降解材料的缺口冲击强度、断裂伸长率达到最大,此后随着nano Kaolin质量百分比增加,而呈下降趋势;在室外自然条件下,经过土埋一段时间后的降解实验,PBS/poly(3HB-co-4HB)/nano Kaolin(100/10/12)复合材料发生了明显的降解,复合降解材料的失重率也已经降到64%左右,说明材料的降解性能较好;纳米复合降解材料熔融剪切储能模量(G′),剪切损耗模量(G″)随着频率的增大呈单增趋势。     

Compositional study and cytotoxicity of biodegradable poly(ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] and poly(ethylene glycol)

Biodegradable PHB–PEG multi-block polyurethane copolymers comprising PHB blocks (M_n: 1100, 1740 and 3240) and PEG blocks (M_n: 1960, 3250, 4150 or 7950) were synthesized followed by characterization by GPC, ¹H NMR, and FT-IR. The PHB contents ranged from 9 to 62% by weight. The copolymers displayed improved thermal stabilities compared with their respective precursors. The morphological structures of the copolymers were studied by FT-IR, DSC and XRD. FT-IR revealed the existence of amorphous and crystalline phases of PHB. Both DSC and XRD analyses showed that separate crystalline phases are formed by PEG and PHB blocks in the copolymers. Upon annealing, the melting transition temperature (T_m), melting enthalpy (ΔH_m) and the fractional crystallinity (X_c) of the PEG block increased when the length of PEG incorporated into the copolymer increased. These values were higher when the PHB block length is shorter as the shorter PHB chain does not disrupt the crystallization of PEG as much as the longer PHB chain. A similar disruptive effect on the crystallization of PHB segments was observed by varying PEG chain lengths but the effect is less pronounced compared with the PEG segments. A comparison of the swelling properties of the poly(ester urethane)s showed that the length and crystalline properties of the PHB block significantly affects the water uptake properties of the copolymers. The crystalline properties and the water uptake capacities of the copolymers could be fine-tuned by consideration of the length of the PHB and PEG block incorporated. The results of the cytotoxicity tests demonstrated that the poly(PHB/PEG) urethanes were non-cytotoxic and could potentially be used for biomedical purposes.     

Transcrystallization kinetics at the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/hemp fibre interface

Transcrystallization of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) on hemp fibres was investigated using polarized optical microscopy. Nucleation and growth of crystals of the transcrystalline region (TCR) were measured during isothermal treatments of samples located in a hot stage. The nucleation rate, nucleation density at saturation and growth rate of the TCR, were determined at crystallization temperatures between 320 and 363 K.The growth rate of crystals in the TCR is the same as that of spherulites in the bulk. Nucleation at the hemp fibres was properly described in terms of the heterogeneous nucleation theory and the transcrystalline growth agrees with the kinetics theory of polymer crystallization. From the empirical data we determined that the interfacial free energy difference function of PHBV on hemp fibres is Δσ = 4.4 erg/cm², lower than the one in the bulk. This indicates that the substrate is not neutral but contributes to the formation of the TCR.From the intensity of the depolarization light, measured under different cooling rates, we determined the activation energies for crystallization in the bulk and transcrystallization.     

Isothermal crystallization kinetics of Ni60Nb4o-xCrx,glasses

Isothermal crystallization kinetics of Ni₆₀Nb_40-xCr_x (x = 0, 5, and 13 at %) glasses was investigated by differential scanning calorimetry. It was possible to separate out the kinetics of formation of various phases which are obtained on crystallization of these glasses. The results are compared with the earlier investigations [1] in which the data were obtained by constant heating rate experiments. The crystallization of M-phase, Ni₃Nb and NbCr₂ phases could be described by Johnson-Mehl-Avrami kinetics. The activation energies for the formation of these phases were found to decrease in the same order. A decreasing activation energy with increasing transformed fraction (time) was also observed. The results are interpreted in light of the values obtained for Avrami exponents.     

Nonisothermal crystallization kinetics of poly(ethylene terephthalate) nanocomposites

This article reports the nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nanocomposites. The non-isothermal crystallization behaviors of PET and the nanocomposite samples are studied by differential scanning calorimetry (DSC). Various models, namely the Avrami method, the Ozawa method, and the combined Avrami-Ozawa method, are applied to describe the kinetics of the non-isothermal crystallization. The combined Avrami and Ozawa models proposed by Liu and Mo also fit with the experimental data. Different kinetic parameters determined from these models prove that in nanocomposite samples intercalated silicate particles are efficient to start crystallization earlier by nucleation, however, the crystal growth decrease in nanocomposites due to the intercalation of polymer chains in the silicate galleries. Polarized optical microscopy (POM) observations also support the DSC results. The activation energies for crystallization has been estimated on the basis of three models such as Augis-Bennett, Kissinger and Takhor methods follow the trend PET/2C20A < PET/1.3C20A < PET, indicating incorporation of organoclay enhance the crystallization by offering large surface area.     

Crystal morphology,mechanical property and non-isothermal crystallization kinetics of poly(trimethylene terephthalate)/maleinized poly(ethylene-octene) copolymer binary blends

The crystal morphology, impact strength and nonisothermal crystallization kinetics of poly(trimethylene terephthalate)/maleinized poly(ethylene-octene) (PTT/PEO-MA) copolymer blends were studied by using the polarized optical microscopy, impact tester and differential scanning calorimetry (DSC). Avrami theory modified by Jeziorny, Ozawa and Mo theories were used to study the non-isothermal crystallization kinetics of the blends, respectively. The results suggest that these methods are suitable for analyzing the crystallization kinetics of the PTT/PEO-MA blends. The PEO-MA component, serving as a nucleation agent in blends, can increase the start crystallization temperatures and accelerate the crystallization rate of the blends. The crystal dimensions are predominantly three-dimensional growths, judged from the Avrami exponent n and the Ozawa exponent m, but the spherulites in blends are much smaller than those in pure PTT. The crystallization active energy suggests that the PEO-MA component can make the PTT component easy to crystallize in blends. The blend has the highest Izod impact strength as PEO-MA content is 3wt.%. Considering both the crystallization kinetic analyses results and the crystal morphology of the blends, the modified Avrami method is believed to be the most useful in reflecting the crystallization of the blends.     

Crystal morphology, mechanical property and non-isothermal crystallization kinetics of poly(trimethylene terephthalate)/maleinized poly(ethylene-octene) copolymer binary blends

The crystal morphology, impact strength and nonisothermal crystallization kinetics of poly(trimethylene terephthalate)/maleinized poly(ethylene-octene) (PTT/PEO-MA) copolymer blends were studied by using the polarized optical microscopy, impact tester and differential scanning calorimetry (DSC). Avrami theory modified by Jeziorny, Ozawa and Mo theories were used to study the non-isothermal crystallization kinetics of the blends, respectively. The results suggest that these methods are suitable for analyzing the crystallization kinetics of the PTT/PEO-MA blends. The PEO-MA component, serving as a nucleation agent in blends, can increase the start crystallization temperatures and accelerate the crystallization rate of the blends. The crystal dimensions are predominantly three-dimensional growths, judged from the Avrami exponent n and the Ozawa exponent m, but the spherulites in blends are much smaller than those in pure PTT. The crystallization active energy suggests that the PEO-MA component can make the PTT component easy to crystallize in blends. The blend has the highest Izod impact strength as PEO-MA content is 3 wt.%. Considering both the crystallization kinetic analyses results and the crystal morphology of the blends, the modified Avrami method is believed to be the most useful in reflecting the crystallization of the blends.