Compósitos de nanocelulose / PHBV: manta microfibrilica por eletrofiação

Pós-graduação em Engenharia Mecânica - FEG

Biodegradation of films of low density polyethylene (LDPE), poly(hydroxibutyrate-co-valerate) (PHBV), and LDPE/PHBV (70/30) blend with Paecilomyces variotii

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Biodegradation of PP and PE blended with PHBV in soil samples

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Mesoporous bioglass/silk composite scaffolds for bone tissue engineering

In the past 20 years, mesoporous materials have been attracted great attention due to their significant feature of large surface area, ordered mesoporous structure, tunable pore size and volume, and well-defined surface property. They have many potential applications, such as catalysis, adsorption/separation, biomedicine, etc. [1]. Recently, the studies of the applications of mesoporous materials have been expanded into the field of biomaterials science. A new class of bioactive glass, referred to as mesoporous bioactive glass (MBG), was first developed in 2004. This material has a highly ordered mesopore channel structure with a pore size ranging from 5–20 nm [1]. Compared to non-mesopore bioactive glass (BG), MBG possesses a more optimal surface area, pore volume and improved in vitro apatite mineralization in simulated body fluids [1,2]. Vallet-Regí et al. has systematically investigated the in vitro apatite formation of different types of mesoporous materials, and they demonstrated that an apatite-like layer can be formed on the surfaces of Mobil Composition of Matters (MCM)-48, hexagonal mesoporous silica (SBA-15), phosphorous-doped MCM-41, bioglass-containing MCM-41 and ordered mesoporous MBG, allowing their use in biomedical engineering for tissue regeneration [2-4]. Chang et al. has found that MBG particles can be used for a bioactive drug-delivery system [5,6]. Our study has shown that MBG powders, when incorporated into a poly (lactide-co-glycolide) (PLGA) film, significantly enhance the apatite-mineralization ability and cell response of PLGA films. compared to BG [7]. These studies suggest that MBG is a very promising bioactive material with respect to bone regeneration. It is known that for bone defect repair, tissue engineering represents an optional method by creating three-dimensional (3D) porous scaffolds which will have more advantages than powders or granules as 3D scaffolds will provide an interconnected macroporous network to allow cell migration, nutrient delivery, bone ingrowth, and eventually vascularization [8]. For this reason, we try to apply MBG for bone tissue engineering by developing MBG scaffolds. However, one of the main disadvantages of MBG scaffolds is their low mechanical strength and high brittleness; the other issue is that they have very quick degradation, which leads to an unstable surface for bone cell growth limiting their applications. Silk fibroin, as a new family of native biomaterials, has been widely studied for bone and cartilage repair applications in the form of pure silk or its composite scaffolds [9-14]. Compared to traditional synthetic polymer materials, such as PLGA and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), the chief advantage of silk fibroin is its water-soluble nature, which eliminates the need for organic solvents, that tend to be highly cytotoxic in the process of scaffold preparation [15]. Other advantages of silk scaffolds are their excellent mechanical properties, controllable biodegradability and cytocompatibility [15-17]. However, for the purposes of bone tissue engineering, the osteoconductivity of pure silk scaffolds is suboptimal. It is expected that combining MBG with silk to produce MBG/silk composite scaffolds would greatly improve their physiochemical and osteogenic properties for bone tissue engineering application. Therefore, in this chapter, we will introduce the research development of MBG/silk scaffolds for bone tissue engineering.

PBT/HIPS枘混体系的结构与性能及生物隆解聚合物结晶性能的研究

以过氧化二异丙苯(DCP)为引发剂，甲基丙烯酸缩水甘油醋(GMA)为活性单体对HIPS进行熔融接枝，制得了功能化的高抗冲苯乙烯(HIPS－g－GMA）。比较HIPS－g－GMA和纯的HIPS的红外谱图，可以看到在HIPS－g－GMA的谱图上出现了一个新的吸收峰，即1730cm~(-1)处的C=O的伸缩振动吸收峰，它为接枝的GMA中的醋基基团的特征峰，因此可以确定GMA己经接枝到HIPS上。能谱分析也提供了相似的结论。同时研究了单体浓度和DCP用量对产物接枝率的影响。用化学滴定方法测定了接枝物的接枝率。随着GMA量的增加，接枝率也随之增加，当GMA用量超过14％时，接枝率趋于平缓；接枝率随DCP量增加而增加。采用DSC、SEM, WAXD, DMA及力学性能等方法和手段研究PBTIHIPS和PBT/HIPS-g-GMA二元共混体系的结晶、形态结构、动态力学性能及力学性能随组成的变化。当PBT为分散相，在增容体系中的PBT出现了分级结晶现象，结晶温度降低，这是由于分散相更为精细的结果。DMA结果表明，在PBTIHIP S-g-GMA体系中由于发生了化学反应，有接枝共聚物生成，体系中两个聚合物的Tg松弛均出现了较明显的降低，增容后体系的力学性能有显著提高。采用DSC, SEM, DMA及力学性能等方法和手段研究PBT/HIPS/HIPS-g-GMA三元共混体系的结构与性能。结果表明PBT无论是分散相还是连续相，HIPS-g-GMA的作用表现为：（1）对PBTIHIPS体系的熔融和结晶行为产生了明显的影响，使PBT的结晶速率变慢，结晶度降低，结晶尺寸分布变宽，结晶完善性变差；（2）改善了共混体系的相容性。未增容体系的形态结构为锐型界面，分散相粒子同基材相连接处清晰缝隙表明两组分间界面粘接很差，为典型的不相容两相形态结构；而加入功能化接枝物的体系的分散相粒子明显变小且分布均匀，甚至难以分辨两相结构的界面；（3）提高了体系的力学性能。在多官能团单体存在下，辐照对PBTIHIPS产生影响。（1）对共混体系的熔融和结晶行为产生影响，使共混体系中的PBT的熔点降低，熔程变宽，结品度下降，结晶速率变慢，结晶尺寸分布变宽，结晶完善性变差；（2）辐射引发多官能团单体反应，使体系的两个Tg松弛发生内移，表明体系的相容性得到改善；（3）当PBT为连续相时，辐射引发的多官能团单体反应对体系的形态结构影响不如化学增溶剂HIPS-g-GMA的效果显著，含有TMPTA的体系的形态结构要好于TAIL o当PBT为分散相，体系的形态结构变化很大，分散相尺寸明显变下小，且分布均匀；（4）辐射改性能提高PBT为分散相的共混体系的力学性能。利用DSC研究了不同成核剂对生物降解聚合物PHBV的结晶性能的彩响。结果表明：（1)添加的成核剂均能影响PHBV的结晶和熔融行为，提高PHBV的结晶速率和使PHBV的结晶更加完美；（2）所有的成核剂均能降低PHBV的结晶自由能；（3）成核剂对PHBV的影响依次为BN, talc, Tb_2O_3和La_2O_3。

聚（3-羟基烷酸酯）的改性研究

该论文目的是改性细菌合成的聚(3-羟基丁酸酯)(PHB)及其共聚物(PHBV),采用交联或共混的方法,改变其聚集态结构或超分子结构,从而改善其力学性能.加深对高聚物结构与性能之间关系,高聚物结晶规律、及特殊相互作用在高聚物中作用的认识.1.采用反应性加工,用过氧化二异丙苯(DCP)引发PHBV的自由基链转移反应,产生了支化和交联的化学结构.2.用交联助剂二苯甲撑双马来酰亚胺(BMI)实现了PHBV的γ-辐射交联.交联的PHBV熔点和结晶度下降.3.双酚A(BPA)在PHBV/BPA共混物中起到了物理交联剂的作用.4.氢键交联结构使PHBV的链段运动受限,结晶速率下降.5.对叔丁基苯酚(TBP)在PHBV中形成了氢键接枝的超分子结构.6.经过溶液共混,BPA在PHB中起到了物理交联剂的作用,使PHB的断裂伸长率从3%提高到45%.8.二醋酸纤维素(CDA)与PHBV经溶液共混(混合溶剂氯仿/丙酮),PHBV的力学性能没有改善,原因可能是CDA-PHBV分子间的氢键作用较弱,组分间发生严重相分离,不利于性能提高.

可生物降解脂肪族聚酯的反应接枝与相形态

聚（β-轻基丁酸醋-co-β-经基戊酸酷）（PHBV）是一种生物降解脂肪族聚酷，其结晶成核密度低，结晶速度比较慢且易生成大尺寸的球晶。以球晶中心向外扩展形成许多圆环状的开裂以及沿球晶生长方向形成许多劈裂，从而导致了PHBV呈脆性断裂。只要能有效地降低其结晶度，减小球晶尺寸，就可以达到增韧的目的。通过PHBV与二氧化碳一环氧丙烷共聚物（PPC）反应接枝来调控PHBV的结构和相形态，具有实际的理论意义和应用前景。开展了PPC的封端和与PHBv的接枝反应。首次提出了甲基丙烯酸缩水甘油醋（GMA）与PHBV及PPC与PHBV－GMA的接枝反应机理。确信PHBV接枝GMA的接枝点发生在PHBV骨架上的季碳原子上，反应过程中没有交联反应和降解反应的发生。发现PHBv-g-Gh1A共聚物上环氧基能与封端的PPc上的梭基熔融反应原位生成了PHBv-g-PPC共聚物。在机械共混物中两大分子之间的接枝和醋交换反应几乎不发生。GMA的引入阻止了PHBV的降解行为，从而改善了PHBV的加工性能。成功地调控了PHBVPC结构及相形态。证实了PHBV与PPC在反应共混过程中的接枝反应。加入PPC阻碍了PHBV的结晶，这在反应体系中更加明显。通过控制反应条件和反应物的组成，可以使非反应共混物中PHBV球晶变得不规则，发生扭曲变形，球晶尺寸降低；而在反应共混物中，可以使其球晶已很难辨认。SEM结果表明在PHBV用PC（30／70）和PHBV用PC（70／30）共混物中发生了相转变。尤其在反应共混物中淬断面表现为塑性。力学性能随共混组成而发生较大幅度的改变。发现通过改变组成及对反应共混相结构的控制，PHBV共混物的断裂伸长率可变化1一2个数量级，从而实现了制得一系列从脆性断裂塑料到高韧性弹性体的高分子材料。研究了反应接枝共混体系的熔融、结晶行为、等温和非等温结晶动力学。发现加入的GMA对PHBV有成核作用。引入的PPC阻碍了PHBV的结晶，降低PHBV的结晶度，球晶径向生长速率，平衡熔点和结晶能力。结晶速率与冷却速率有较大的依赖性。修正的Avrami方程能很好地描述PHBv和PHBv爪PC共混物非等温结晶过程。对动态力学性能的分析发现，反应共混物相比于非反应共混物聚合物玻璃化温度都有不同程度的内移，说明两组分间相容性增加，接枝共聚物具有良好的增容效果，显著地改善了两相界面性能。PHBV可以部分进入PPC相区，使共混物分子运动特征发生改变。发现在熔体加工条件下，PHBV与PPC之间很难发生酷交换反应，但是以辛酸亚锡为催化剂，氯苯为溶剂，在120℃条件下，两者可以发生醋交换反应。在聚己内醋（PCL）用PC熔融共混过程中GMA可以有效地抑制过氧化二异丙苯（DCP）所引起的PCL交联反应。在DCP和OMA存在下得到的样品之球晶具有十字消光现象，球晶规整度增大。同在溶液中醋交换催化剂存在下PPC和PCL发生了酷交换反应后所形成的球晶相结构相类似，而PCL／PPCOCP体系所形成的球晶中含有大量的非晶相区。从而，确信了GMA在脂肪族聚醋，脂肪族聚碳酸醋等生物降解高分子反应共混体系中的双重作用：一是引入具有高反应活性的官能团；二是减少在过氧化物作用下PHBV类高分子的降解及PCL类高分子的交联反应。PCL共混组分可以提高PPC相区的稳定性。提高反应时间或催化剂浓度同样能够改善热稳定性。

玉米淀粉的化学与物理修饰

本论文以淀粉为研究对象，从高分子的基本理论出发，通过化学与物理的手段利用淀粉上的经基，调控了淀粉大分子链的聚集态结构，探索了将淀粉这种天然储能高分子变为实用的材料的可能性。采用化学交联的手段制备了交联淀粉膜。研究了淀粉交联后的老化过程和水在其中的结合状态。试验证明，交联键的引入使得淀粉的结晶和局部有序结构程度下降，让淀粉大分子的聚集态结构趋于均一化的同时，释放出大量的"自由轻基"。改变了淀粉膜的吸水能力和淀粉内部水分子的结合状态，综合交联与水分子的增塑作用，可以在一定程度上调控淀粉膜的力学性能。淀粉和生物降解大分子（PCL、PHBV）制备的IPN材料显著的提高了淀粉的耐水性能。通过实验证明DMSO／water配合体系作为一种高效、安全的组合溶剂对淀粉的醚化反应非常有效，取代度最高可达1．81。控制节基氯和淀粉重复单元的摩尔比、反应温度、DMSO/water组合溶剂的不同配比等可以制备出不同取代度的节基淀粉醚。经证实，淀粉的醚化反应主要发生在脱水葡萄糖环上的2位碳原子的经基上，其次发生在C-6、C-3碳原子的经基上。醚化后的淀粉即使很低的取代度（Ds：0．0546）时淀粉在x一射线衍射曲线上的结晶峰已经完全消失了。发现了稳定、高效的淀粉增塑剂FSDT。使用FSDT成功的对淀粉进行了塑化处理，而且塑化后的淀粉一年后仍保持优良的机械性能，特别是当FSDT的含量超过30％以后，淀粉从无法加工的脆性材料变成了类似弹性体的材料，在此基础对淀粉进行了化学交联，交联后样品的断裂伸长率有了更进一步的提升，达到470％。

聚3-羟基烷酸酯异相成核结晶的研究

本论文以具有巨大应用前景的PHBV作为研究对象，针对PHBV结晶速率低，易产生二次结晶，从而严重影响其加工性能和力学性能的稳定性等方面的缺点，根据PHBV的分子结构和脆性的机理分析，试图采用添加成核剂的方法，提高PHBV的结晶速率和结晶度，从而缩短PHBV的加工成型周期，控制其聚集态结构，提高其制品的稳定性，改善材料的物理力学性能。并在此基础上，探讨PHBV异相成核结晶的机理，加深成核剂对聚合物有效成核机理的认识，更好的理解聚合物结晶过程。1．添加成核剂的量达到0.5wt％时，对苯二甲酸（TPA）对PHBV起到了显著的结晶成核作用。结晶起始温度提高了约20℃，结晶速率达到最大值所对应的温度T_p提高了30℃，结晶烙增加了15J/g，结晶速率提高了4.4倍。这些数据表明，TPA是一种对PHBV极为有效的成核剂。2．加入成核剂TPA的PHBV表现出典型的双熔融行为，主要原因是TPA对PHBV的结晶成核作用和PHBV的熔融再结晶。低温侧的熔融峰对应着PHBV自熔体降温过程形成的结晶，高温侧的对应着PHBV升温过程中形成的结晶。3．TPA的成核作用大大的改变了PHBV的形态结构，使PHBV的球晶尺寸明显减小，球晶数量增大。4．TPA使PHBV晶体在（110）和（020）方向上微晶尺寸变大，晶区和非晶区的电子密度差增大。5．添加0.5wt％的TPA后，PHBV的断裂伸长率从4％提高到10％。6．TPA、IPA、淀粉和山梨醇对PHBV的结晶都具有很明显的成核作用，其原因可能是化学结构上都具有极性基团。7．红外光谱研究没有能够有效的给出PHBV与TPA是否存在特殊相互作用，从而导致TPA对PHBV的结晶成核作用的证据，但是，PHBV拨基伸缩振动谱带随温度的变化却给出了TPA对PHBv的结晶成核作用始于160℃高温。

Modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate) using hydrogen bonding monomers

Properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were significantly modified by a hydrogen bonding (H-bond) monomer-bisphenol A (BPA). BPA lowered the T-m of PHBV and widened the heat-processing window of PHBV. At the same time, a dynamic H-bond network in the blends was observed indicating that BPA acted as a physical cross-link agent. BPA enhanced the T, of PHBV and reduced the crystallization rate of PHBV. It resulted in larger crystallites in PHBV/BPA blends showed by WAXD. However, the crystallinity of PHBV was hardly reduced. SAXS results suggested that BPA molecules distributed in the inter-lamellar region of PHBV. Finally, a desired tension property was obtained, which had an elongation at break of 370% and a yield stress of 16 MPa. By comparing the tension properties of PHBV/BPA and PHBV/tert-butyl phenol blends, it was concluded that the H-bond network is essential to the improvement of ductility.

Crosslinking of poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] using dicumyl peroxide as initiator

In order to modify poly [(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV), the crosslinking of this copolymer was carried out at 160degreesC using dicumyl peroxide (DCP) as the initiator. The torque of the PHBV melt showed an abrupt upturn when DCP was added. Appropriate values for the gel fraction and crosslink density were obtained when the DCP content was up to 1 wt% of the PHBV. According to the NMR spectroscopic data, the location of the free radical reaction was determined to be at the tertiary carbons in the PHBV chains. The melting point, crystallization temperature and crystallinity of PHBV decreased significantly with increasing DCP content. The effect of crosslinking on the melt viscosity of PHBV was confirmed as being positive. Moreover, the mechanical properties of PHBV were improved by curing with DCP. When 1 wt% DCP was used, the ultimate elongation of PHBV increased from 4 to 11 %. A preliminary biodegradation study confirmed the total biodegradability of crosslinked PHBV.