Structure and properties for transparent polypropylene containing sorbitol‐based clarifier

Relation between structure and properties is studied for polypropylene (PP) containing 1,3:2,4‐di‐benzylidene sorbitol (DBS) that forms network structure composed of nanofibrils in a molten PP. It is found that the aggregation state of DBS, which can be controlled by the applied flow field and thermal history, affects the spherulite texture of PP and thus the transparency. When injection‐molded products, in which the nanofibrils of DBS orient to the flow direction, are reprocessed at 180 °C, that is, lower temperature than the melting point of DBS, the obtained material shows high level of transparency, although it has been believed that sorbitol‐derivatives have to be melted and dissolved into the molten PP at high temperature, for example, 240 °C. Further, it is found that the particle flow occurs in the blend at 180 °C. The applied shear force generates the particles, that is, flow units, by the fragmentation of the network structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 41–47, 2008     

In silico studies of 1,3(R):2,4(S)‐dibenzylidene‐D‐sorbitol as a gelator for polypropylene

The organic gelator 1,3(R):2,4(S)‐dibenzylidene‐D‐sorbitol (DBS) self‐organizes to form a 3‐D network at relatively low concentrations in a variety of nonpolar organic solvents and polymer melt. In this work, we have investigated the interactions between DBS molecules in polypropylene (PP) by molecular modeling. We have used quantum mechanics to elucidate the preferred geometry of one molecule and a dimer of DBS, and molecular mechanics and molecular dynamics to simulate pure DBS, pure PP, and mixture of DBS and PP as condensed phases, at various temperatures. It was found that inter‐ and intramolecular H‐bonds between DBS molecules are formed in PP in a much more pronounced manner than those formed in pure DBS. The most significant intermolecular H‐bonds are formed between the terminal hydroxyl groups. The most significant intramolecular H‐bonds are formed between O5 /H‐O6 groups. Due to the H‐bonds, DBS molecules form a rigid structure similar to liquid crystal forming molecules, which might explain their tendency to create nanofibrils. It seems that the aromatic rings do not contribute significantly to the intermolecular interactions. Their main role is probably to stiff the molecular structure. Temperature dependences of inter‐ and intramolecular interactions are different. Whereas intermolecular interactions peak heights decrease when temperature increases for pure DBS, the intramolecular interaction almost does not change. Copyright © 2012 John Wiley & Sons, Ltd.     

Fibril formation of 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol in a polypropylene melt

Binary mixtures of 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS) within the melt of polypropylene (PP) were studied at DMDBS contents of 0.4 and 1.0 wt %. DMDBS serves as a nucleating agent in PP crystallization by formation of a nanofibrillar network. The kinetics of the DMDBS solidification process within the PP melt and the ensuing nanofibrillar structure were studied by in situ small-angle X-ray scattering (SAXS) analysis combined with imaging by electron microscopy. The dynamic lag of the fibrillar structure formation kinetics and its temperature dependence indicate a nucleation and growth mechanism, controlled by the rate of nucleation. Investigation of the fibrillar structure by electron microscopy indicates a complex structure in which long and thin fibrils (less than 100 nm in cross-section) are composed of thinner nanofibrils (less than 10 nm in cross-section).     

Network formation of a phenyl vinyl ketone copolymer with 4-vinylbenzil and its photodecrosslinking in films

The irradiation (λ > 400 nm) in air of a copolymer of phenyl vinyl ketone with 4-vinylbenzil (VBZ) containing 1.5 wt % VBZ structural units in film, followed by the thermal decomposition of the resulting pendant benzoyl peroxide groups, leads to crosslinking. The subsequent irradiation of the crosslinked polymer at 366 nm results in the cleavage of the poly(phenyl vinyl ketone) chain between the junction points of the polymer network through a Norrish type II reaction. Therefore, poly(phenyl vinyl ketone-co-4-vinylbenzil) represents a novel type of photoresist based on polymer network decrosslinking. The process involves three steps: photogeneration of peroxide, crosslinking by its thermal decomposition, and subsequent photodecrosslinking of the polymer network. This material provides positive-tone images after UV exposure (λ > 330 nm) and development in an organic medium such as isopropyl methyl ketone. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 765–771, 2004     

Effect of nucleating agent on the brittle–ductile transition behavior of polypropylene/ethylene–octene copolymer blends

In the present work, α‐form nucleating agent 1,3:2,4‐bis (3,4‐dimethylbenzylidene) sorbitol (DMDBS, Millad 3988) is introduced into the blends of polypropylene/ethylene–octene copolymer (PP/POE) blends to study the effect of the nucleating agent on the toughness of PP/POE blends through affecting the crystallization behavior of PP matrix. Compared with the PP/POE blends, in which the toughness of the blends increases gradually with the increasing content of POE and only a weak transition in toughness is observed, addition of 0.2 wt % DMDBS induces not only the definitely brittle‐ductile transition at low POE content but also the enhancement of toughness and tensile strength of the blends simultaneously. Study on the morphologies of impact‐fractured surfaces suggests that the addition of a few amounts of DMDBS increases the degree of plastic deformation of sample during the fracture process. WAXD results suggest that POE induces the formation of the β‐form crystalline of PP; however, DMDBS prevents the formation of it. SEM results show that the addition of DMDBS does not affect the dispersion and phase morphologies of POE particles in PP matrix. DSC and POM results show that, although POE acts as a nucleating agent for PP crystallization and which enhances the crystallization temperature of PP and decreases the spherulites size of PP slightly, DMDBS induces the enhancement of the crystallization temperature of PP and the decrease of spherulites size of PP more greatly. It is concluded that the definitely brittle–ductile transition behavior during the impact process and the great improvement of toughness of the blends are attributed to the sharp decrease of PP spherulites size and their homogeneous distribution obtained by the addition of nucleating agent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 577–588, 2008     

Nucleating and clarifying agents for polyolefins

Nucleating agents are used in semi‐crystalline polymer systems (mainly polyolefins) to increase the rate of crystallization. These agents increase degree of crystallinity and lamellae thickness and, hence, improve stiffness and strength. In addition to altered mechanical characteristics, clarifying agents do also improve optical properties. This paper provides a brief overview on nucleating/clarifying agents. The efficiency of such products (e.g. Na‐benzoate, sorbitol acetals) for polypropylene (PP homopolymer, PP copolymer) is evaluated. The clarifiers Irgaclear D ((1,3:2,4)‐dibenzylidene sorbitol) and Irgaclear DM (1,3:2,4‐Bis‐(p‐methylbenzylidene) sorbitol) provide a 3‐dimensional fibrillar structure upon cooling from the polymer melt. This magnified nucleation density yields spherulites with reduced size (< 1micron) ‐ in comparison to non‐nucleated products. Addition of Irgaclear to polypropylene leads to increased clarity, reduced haze and enhanced stiffness of molded parts. Higher recrystallization temperatures results in shorter cycle times and increased throughput during the molding process.     

Can random copolymers serve as effective polymeric compatibilizers?

We investigate the compatibilizing performance of a random copolymer in the melt state, using transmission electron microscopy. Blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) are chosen as a model system, and a random copolymer of styrene and methyl methacrylate (SMMA) with 70 wt % styrene is used as a compatibilizer. From TEM photographs it is clear that SMMA moves to the interface between PS and PMMA domains during melt mixing, and forms encapsulating layers. However, the characteristic size of the dispersed phase increases gradually with annealing time for all blend systems studied. This demonstrates that the encapsulating layer of SMMA does not provide stability against static coalescence, which calls into question the effectiveness of random copolymers as practical compatibilizers. We interpret the encapsulation by random copolymers in terms of a simple model for ternary polymer blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2835–2842, 1997     

Physical organogels composed of amphiphilic block copolymers and 1,3:2,4-dibenzylidene-D-sorbitol

The 1,3:2,4-dibenzylidene-D-sorbitol (DBS) molecule is capable of self-organizing into nanoscale fibrils through intermolecular forces such as hydrogen bonding and pi interactions. At sufficiently high concentrations (typically less than approximately 2 wt%), the nanofibrils can form a network that promotes physical gelation of the matrix medium. Previous studies have investigated the mechanism of DBS-induced gelation and the features of DBS-containing gels in poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). In this work, we examine the effect of adding DBS to a series of amphiphilic PPG-b-PEG-b-PPG triblock copolymers differing in composition and molecular weight. Dynamic rheological measurements reveal that the resultant gels are thermoreversible (i.e., they exhibit comparable mechanical properties before dissolution and after reformation under quiescent conditions), exhibiting a maximum in the elastic modulus (G') at temperatures near the gel dissolution (T(d)) and formation (T(f)) temperatures. Both T(d) and T(f) tend to increase with increasing DBS concentration and PPG content, and their difference decreases with increasing PPG fraction in the copolymer. The magnitude of G' is sensitive to copolymer composition and polymer identity at low DBS concentrations, but becomes polymer-independent as the DBS network saturates at concentrations in excess of approximately 1 wt%.     

NMR characterization of the formation kinetics and structure of di-O-benzylidene sorbitol gels self-assembled in organic solvents

The molecule 1,3:2,4-di-O-benzylidene sorbitol (DBS) is a common "gelator" that forms thermally reversible gels in diverse organic solvents. Solid-state (13)C and (1)H NMR techniques, along with electron microscopy, are utilized in an exploratory study of DBS in the gelled state where we consider both in situ and dried gels. The gels were formed in either acetone or benzene, with the former being a better solvent for DBS. We find the in situ or dried DBS gels to be composed of rigid twisted nanofibrils (～15 to 21 nm in diameter). The fibrils show local molecular ordering, but not crystalline order, and they contain no trapped solvent. The molecular mobility at the fibril surface is modestly enhanced, and all the free hydroxyl groups of the sorbitol moiety are involved in strong hydrogen bonding. We also attempted to find a truly crystalline form of DBS whose structure, as judged by the similarity of (13)C spectra, is close to that of the fibrils. We partially succeeded in this quest, employing melt crystallization followed by slow cooling. However, this sample was a mixed crystal having small domains, where only one type of domain was structurally similar to the fibrils. We also investigated the long-time evolution of the in situ DBS gel network. Specifically, high-resolution NMR kinetic studies were performed over periods of days where the residual concentration of DBS in acetone solution was monitored during and after gel formation. The DBS concentration on these long timescales evolved slowly, and we introduce a simple mathematical model and equation to describe this phenomenon.     

Nucleating Agents in Polypropylene

The effects of nucleating agents such as dibenzylidene sorbitol (DBS) (a derivative of sorbitol), pine crystal 1500, sodium and potassium benzoates in commercial grade isotactic polypropylene iPP are studied using differential scanning calorimetry (DSC). Isothermal crystallization kinetics of polypropylene to the alpha phase have been analyzed using Avrami's model. Results indicate that dibenzylidene sorbitol and pine crystal are very effective in increasing the crystallization temperature of the polymer and number of nuclei formed during crystallization.This revised version was published online in November 2005 with corrections to the Cover Date.     

Improved Dental Composites Utilizing Dibenzylidene Sorbitol Networks

Dibenzylidene sorbitol (DBS) is a sugar derivative that is capable of self-organizing into a 3D nanofibrillar network at relatively low concentrations in a wide variety of organic solvents and polymer melts to induce physical gelation. This research was aimed at determining the effect of DBS networks on vinyl conversion, polymerization shrinkage, and mechanical strength of bioactive dental composites containing zirconyl-modified amorphous calcium phosphate (Zr-ACP) and a polymer matrix derived from the photopolymerization of ethoxylated bisphenol-A dimethacrylate (EBPADMA). Flexural strength was enhanced while polymerization shrinkage and its associated stress development were both significantly reduced by the incorporation of DBS into the composites, suggesting that DBS may be a useful additive for dental composites.     

Mechanical properties of polymer‐blend nanocomposites with organoclays: Polystyrene/ABS and high impact polystyrene/ABS

Thirty‐three polystyrene (PS)/acrylonitrile‐butadiene‐styrene (ABS) and high impact PS/ABS polymer blends with organoclay and copolymer additives were prepared by melt processing using different mixing sequences in order to test the putative capability of clay to perform a compatibilizing role in polymer blends. In general, the addition of clay increased the tensile modulus and had little effect on tensile strength. For the blends studied in this work, the addition of organoclays caused a catastrophic reduction in impact strength, a critical property for commercial viability. The polymer‐blend nanocomposites adopted a structure similar to that for ABS/clay nanocomposites as determined by X‐ray diffraction and transmission electron microscopy. It is suggested that clay reinforcement inhibits energy absorption by craze formation and shear yielding at high strain rates. Simultaneous mixing of the three components provided nanocomposites with superior elongation and energy to failure compared to sequential mixing. The clay pre‐treated with a benzyl‐containing surfactant gave the best overall properties among the various organoclays tested and of the two clay contents studied 4 wt % was preferred over 8 wt % addition. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Crystal phases,structure, and orientation in isotactic polypropylene after isothermal crystallization under oscillatory shear as a function of nucleation agent

2D wide-angle X-ray diffraction (2D-WAXD) measurement was performed to investigate the effects of both oscillatory shear and the nucleating agent on the crystalline structure distribution and orientation of isotactic polypropylene (iPP). 1,3:2,4-bis(p-methylbenzylidene) sorbitol (MDBS) and 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS) can induce α-PP and β-PP simultaneously. The presence of MDBS (or DMDBS) and oscillatory strain (oscillatory frequency is fixed) exhibits a synergistic interaction on increasing the content of β-crystals of iPP. Under the oscillatory shear field at the fixed oscillatory strain, the β-crystal content and the orientation of iPP with and without MDBS (or DMDBS) change slightly with the increase of the oscillatory frequency. Comparing with MDBS (or DMDBS) nucleated iPP crystallization under shear field, the periodically changed flow direction of the oscillatory shear field leads to the shorter α-row nuclei, weaker orientation but more β-crystals of the nucleated iPP.     

Ethylene/vinyl acetate copolymer/clay nanocomposites

This article highlights the history, synthetic routes, material properties, and scope of ethylene/vinyl acetate copolymer (EVA)/clay nanocomposites. These nanocomposites of EVAs are achieved with either unmodified or organomodified layered silicates with different methods. The structures of the resulting polymer/inorganic nanocomposites have been characterized with X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The addition of a small amount of clay, typically less than 8 wt %, to the polymer matrix unusually promotes the material properties, such as the mechanical, thermal, and swelling properties, and increases the flame retardancy of these hybrids. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 471–480, 2006     

Deformation of disentangled polypropylene crystalline grains into nanofibers

It was shown that a solid‐state deformation of polypropylene (PP) being in the form of partially disentangled powder is possible by blending with another molten polymer. During mixing of disentangled polypropylene powder with polystyrene at the temperature below melting of polypropylene crystals the shear forces deform powder grains into nanofibers. All disentangled powder particles larger than 0.7 µm underwent deformation into nanofibers having the mean thickness between 100 and 200 nm. Polypropylene nanofibers got entangled during blending and form a network within polystyrene matrix, reinforcing it. Network of entangled nanofibers can be further deformed with pronounced strain hardening and strength reaching 70 MPa at 135 °C. Blending resulted in generation of PP nanofibers and formation of PP nanofibers entangled network, thus formation of “all‐polymer nanocomposites” in one step compounding. The crucial feature for ultra‐deformation of PP grains by shearing during mixing is disentanglement of macromolecules. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1983–1994     

Interfacial structure and properties of polyurethane/poly(methylacrylate-co-styrene) coating to regenerated cellulose film

A semiinterpenetrating polymer network (IPN) containing 72 wt % polyurethane (PU) and 6 wt % poly(methylacrylate-co-styrene) [P(MA-St)] was coated onto surfaces of regenerated cellulose (RC) film, which was prepared by coagulating a cellulose cuoxam from bagasse pulp. The interfacial structures, bonding manner, and the strength of the coated film were studied by infrared (IR),¹³C nuclear magnetic resonance (NMR), differential thermal analysis (DTA), transmission electron microscopy (TEM), and electron probe microscopy analysis (EPMA). It was shown that the RC film coated with PU/P(MA-St) has strong interfacial interactions, where covalent and hydrogen bonds are formed across the interface between cellulose and the PU/P(MA-St) coating. The interfacial structure of the coated film is regarded as a shared PU network crosslinked simultaneously with P(MA-St) and cellulose film. The tensile strength, water resistivity, and optical transmission of the coated films were considerably higher than that of the uncoated films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2495–2501, 1997     

Semicontinuous heterophase copolymerization of styrene and acrylonitrile

The synthesis of styrene‐acrylonitrile copolymers by semicontinuous heterophase polymerization is reported here. The effect of feed composition at a fixed addition rate of monomer mixture on kinetics, particle size, polymer content, and molar masses, was studied. This process permits the synthesis of nanolatexes containing narrow size‐distribution particles with number‐average diameter (D_n) of about 18 nm, polymer content as high as 23 wt %, and copolymer‐to‐surfactant weight ratios between 23 and 25, depending on monomer feeding rate, which are larger than those reported for microemulsion copolymerization of several comonomers. Copolymers with homogeneous composition similar to the feeding monomers composition were obtained thorough the reaction, which is difficult to achieve by batch polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of a sorbitol nucleating agent on fractionated crystallization of polypropylene droplets

The effect of a sorbitol nucleating agent on crystallization of polypropylene (PP) in droplets was studied. Layer‐multiplying coextrusion was used to fabricate assemblies of 257 layers, in which PP nanolayers alternated with thicker polystyrene (PS) layers. The concentration of a commercial nucleating agent, Millad 3988 (MD) in the layers was varied up to 2 wt %. When the assembly was heated into the melt, interfacial driven breakup of the 12 nm PP layers produced a dispersion of submicron PP particles in a PS matrix. Analysis of optical microscope images and atomic force microscope images indicated that the particle size was not affected by the presence of MD. The crystallization behavior of the particle dispersion was characterized by thermal analysis. In the absence of a nucleating agent, the submicron particles crystallized almost exclusively by homogeneous nucleation at about 40 °C. Addition of a nucleating agent to the PP layers offered a unique opportunity to study the nature of heterogeneous nucleation. Nucleation by MD resulted in fractionated crystallization of the submicron PP particles. The concentration dependence of the multiple crystallization exotherms was interpreted in terms of the binary polypropylene‐sorbitol phase diagram. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1788–1797, 2007     

亚苄基山梨醇衍生物在有机溶剂中的自组装及凝胶化研究

从分子结构的差异、亲溶剂作用、分子几何构型、相转变热焓以及溶剂极性等方面研究了三种亚苄基山梨醇衍生物凝胶剂在有机溶剂中的自组装和凝胶化机理. 三种衍生物凝胶剂在结构上的差别仅在于亚苄基上甲基取代基数量不同. 结果表明: 由于亲溶剂作用的增加和分子几何构型的优化, 含甲基多的凝胶剂在有机溶剂中的自组装能力强, 表现在具有低的最低凝胶化浓度和高的相转变温度. 而溶剂极性的增强, 使三种衍生物凝胶剂形成的凝胶相转变温度降低. 偏光显微镜照片表明该凝胶剂在正辛醇凝胶中的聚集体晶型不同. 场发射扫描电镜照片表明三种衍生物凝胶剂自组装形成相互缠绕的纤维束网络结构. 紫外吸收光谱表明, 对比其溶液态, 三种衍生物聚集体苯环的K带发生红移, 表明π-π堆积作用是亚苄基山梨醇衍生物凝胶剂自组装的驱动力之一; 红移的幅度随苯环上甲基数量的增加而增加, 这与三种衍生物形成的分子凝胶的热稳定性相吻合.     

Film‐formation property of vinylidene chloride‐methyl methacrylate copolymer latex. II. Effect of latex storage temperature

Changes in the minimum film‐formation temperature (MFFT) of 91:9 wt % vinylidene chloride (VDC)‐methyl methacrylate (MMA) latex prepared by the seeded batch process during storage at 5, 20, and 40 °C were investigated. MFFT of the latex rose the fastest at 20 °C. Infrared absorption of fresh and stored latexes and wide‐angle X‐ray diffraction of powder polymers obtained by lyophilization of fresh and stored latexes indicated a much greater increase in polymer crystallinity during latex storage at 20 °C than at 5 and 40 °C. Observed increases in MFFT during latex storage correlated with increases in polymer crystallinity. Infrared absorption of polymer stored at 5–60 °C in the dry state, such as lyophilized polymer and coating film, indicated that a polymer crystallinity increase was greater during storage at higher temperatures. These results showed that crystallization behavior of 91:9 wt% VDC‐MMA copolymer latex differed from that of VDC‐MMA copolymer in the dry state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 948–953, 2002