Membrane formation via thermally induced phase separation in polypropylene/polybutene/diluent system

Porous membranes were prepared from a polymer blend system by the thermally induced phase separation (TIPS) process. The polymer blend system was isotactic polypropylene (iPP)/polybutene (PB) and the diluent was diphenyl ether (DPE). Two types of porous membranes were prepared by the extractions of DPE alone and both DPE and PB after the phase separation. The effect of the addition of PB to the iPP solution on the phase diagram was investigated and the phase separation kinetics was measured by the light scattering method. The addition of PB resulted in the higher solute rejection property and lower water permeance. By the further extraction of PB from the porous iPP/PB membrane prepared by the extraction of DPE, the water permeance was approximately doubled, maintaining almost the same rejection property. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1701–1708, 2002; DOI 10.1002/app.10550     

Formation of porous poly(ethylene‐co‐vinyl alcohol) membrane via thermally induced phase separation

Crystalline poly(ethylene‐co‐vinyl alcohol) (EVOH) membranes were prepared by a thermally induced phase separation (TIPS) process. The diluents used were 1,3‐propanediol and 1,3‐butanediol. The dynamic crystallization temperature was determined by DSC measurement. No structure was detected by an optical microscope in the temperature region higher than the crystallization temperature. This means that porous membrane structures were formed by solid–liquid phase separation (polymer crystallization) rather than by liquid–liquid phase separation. The EVOH/butanediol system showed a higher dynamic crystallization temperature and equilibrium melting temperature than those of the EVOH/propanediol system. SEM observation showed that the sizes of the crystalline particles in the membranes depended on the polymer concentration, cooling rate, and kinds of diluents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2449–2455, 2001     

Characterization of a maleic anhydride-modified polypropylene as an adhesion promoter for glass fiber composites

Isothermal and nonisothermal crystallizations of isotactic polypropylene (iPP), maleic anhydride (MAH)-grafted PP, and MAH-modified iPP were studied by differential scanning calorimetry (DSC), to evaluate the influence of a small amount of MAH-grafted PP in iPP on its crystallization behavior. Isothermal crystallization was followed in the temperature range from 391 K to 403 K, and the rate constant and Avrami exponents were determined. Nonisothermal crystallization was carried out at different cooling rates (1-20 K/min). It was found that the crystallization kinetics of iPP was significantly altered by modification with the MAH-grafted polymer. A decreased equilibrium melting temperature, as well as decreased surface energy of folding and critical dimensions of a growing nucleus, was determined for the MAH-modified iPP, indicating faster growth of lamellae and a higher rate of crystallization. The improved nucleation ability of the modified polymer was shown to cause a shift in the crystallization peak temperature towards higher values (from 393.7 K to 399.6 K, at a cooling rate of 1 K/min), resulting in crystal structures less disposed to recrystallization. Model composites of iPP and MAH-modified iPP with glass fibers were also analysed. The apparent shear strength of single-fiber model composites with MAH-modified iPP was drastically increased compared with homo-iPP.     

Formation and behaviour of low‐temperature melting peak of quenched and annealed isotactic polypropylene

The process of low‐melting point (LMP) α‐phase formation in a quenched and annealed isotactic polypropylene (iPP) was studied by means of differential scanning calorimetry. The influence of preparation conditions (quenching and annealing temperatures, annealing times and sample thickness), together with the measurement parameters (heating and cooling rates), on the iPP melting behaviour are analysed. The results reveal a constant yield of LMP crystals over a wide range of quenching temperatures. This study also suggests that the LMP α‐crystals originate from the crystallization of polymer portions, which are somewhere between the amorphous and the smectic phase on the macromolecular scale of order. © 2001 Society of Chemical Industry     

Formation of microporous membrane of isotactic polypropylene in dibutyl phthalate‐soybean oil via thermally induced phase separation

Isotactic polypropylene (iPP) microporous membranes were prepared via the thermally induced phase separation (TIPS) process with the diluents being dibutyl phthalate (DBP) and soybean oil mixture. By changing the weight ratio of DBP to soybean oil systematically, it was determined experimentally that the cloud‐point curves were influenced to a great extent, while the crystallization curves showed much less dependence on the diluents composition. Scanning electron microscopy (SEM) showed that the resulting membrane morphologies changed significantly by varying the composition of the diluents, i.e., by changing the interaction parameter and other characteristics of diluents, the interwoven or celluar structure can be fabricated successfully at a fixed polymer concentration under the same cooling conditions. Different growth rates of iPP spherulite were obtained in the diluents with different composition. It is shown that the spherulites growth rates may be also attributed to the great variations of the final microporous morphology to a certain extent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Description of PVT behavior of an industrial polypropylene–EPR copolymer in process conditions

An experimental procedure is presented to describe the PVT behavior of multiphase polymeric materials in a wide range of cooling rates. In particular, the procedure is applied to a typical multiphase industrial polymer, that is, an industrial polypropylene–ethylene‐propylene rubber (iPP–EPR) copolymer with a small percentage of talc. The volume evolution is described combining specific volumes of different phases present in the material. All phases are described simply by thermal expansion and compressibility coefficients drawn either from the literature or from low and high temperature (i.e., below and above the iPP crystallization range) standard PVT data. Crystallization evolution of iPP is described by the Nakamura nonisothermal formulation of the Avrami–Evans crystallization kinetic model. Model parameters are identified by comparison with both standard calorimetric results and final densities of thin samples solidified during quenches conducted with cooling rates of several hundreds of K/s. It is also shown that identification of crystallization kinetic parameters by means of calorimetric data only leads to misleading results for cooling rates larger than those adopted in the calorimetric tests. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 267–278, 2001     

Temperature and crystallinity profiles generated in a polycaprolactone/starch blend under different cooling conditions

This work concerns the numerical simulation of the temperature profiles and the degree of crystallinity through the thickness of a part made from a commercial biodegradable material based on caprolactone and starch (Mater‐Bi Z), as a function of the cooling conditions from the melt. The crystallization kinetics during cooling conditions was evaluated experimentally by calorimetry and the Kamal–Chu equation was used to describe the degree of crystallinity developed during constant cooling rate experiments. This equation coupled with the thermal energy equation, through a heat source term, described the heat generated during crystallization of the polymer. The numerical solution of the system of differential equations was obtained using an implicit finite‐difference method. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3275–3283, 2001     

A novel β‐nucleating agent for isotactic polypropylene

The nucleating ability of p‐cyclohexylamide carboxybenzene (β‐NA) towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry, X‐ray diffraction, polarized optical microscopy and scanning electron microscopy. β‐NA is identified to have dual nucleating ability for α‐iPP and β‐iPP under appropriate kinetic conditions. The formation of β‐iPP is dependent on the content of β‐NA. The content of β‐phase can reach as high as 96.96% with the addition of only 0.05 wt% β‐NA. Under non‐isothermal crystallization the content of β‐iPP increases with increasing cooling rate. The maximum β‐crystal content is obtained at a cooling rate of 40 °C min^–1. The supermolecular structure of the β‐iPP is identified as a leaf‐like transcrystalline structure with an ordered lamellae arrangement perpendicular to the special surface of β‐NA. Under isothermal crystallization β‐crystals can be formed in the temperature range 80–140 °C. The content of β‐crystals reaches its maximum value at a crystallization temperature of 130 °C. © 2012 Society of Chemical Industry     

Porous polyphenylene sulfide membrane with high durability against solvents by the thermally induced phase‐separation method

Porous polyphenylene sulfide membranes were prepared as new solvent‐resistant membranes by the thermally induced phase‐separation (TIPS) method. Porous structures were either formed by solid–liquid phase separation (polymer crystallization) or liquid–liquid phase separation. The effects of solvents, cooling rates, and polymer concentrations on the porous structures were investigated. Various characteristics of pore structure can be obtained with suitable diluents and cooling rates using the TIPS method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2959–2966, 2006     

Effect of vibration on crystal morphology and structure of isotactic polypropylene in nonisothermal crystallization

An experimental study on crystal structure and morphology of isotactic polypropylene (iPP) subjected to vibration was carried out on a laboratory apparatus. Crystallite size, crystal structure, and crystallinity of iPP under vibration or nonvibration were investigated through differential scanning calorimeter (DSC), wide angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). The results reveal that at high cooling rate, the crystallinity of samples under vibration decreases, and at low cooling rate it remains constant because of chain relaxation. On the other hand, the sizes of the iPP spherulites under vibration decrease as compared with those without vibration. Taking the relaxation of the iPP chain into consideration, we believe that the influence of vibration conditions on the main α‐form of the iPP crystal is rather complex. An obvious increase of β‐form content in the crystal phase results from the imposition of vibration. The results indicate that the content of β‐iPP is dependent on vibration amplitude and time. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2187–2195, 2004     

Nonisothermal crystallization of isotactic polypropylene blended with poly(α-pinene). I. Bulk crystallization

The influence of a natural terpene resin, poly(α-pinene) (PαP), on the nonisothermal crystallization process of isotactic polypropylene (iPP) was investigated. The solidification process strongly depends on cooling rate, composition, and miscibility of the system. For the blends containing PαP up to 30 wt %, the overall nonisothermal crystallization rate is depressed with respect to plain iPP. This is probably the result of the diluting effect of the polyterpene because the two components are miscible. The 50/50 blend presents, instead, two amorphous phases: an iPP-rich phase and a PαP-rich phase. For this composition, solidification starts at temperatures higher than those for plain iPP and blends with lower PαP content, given that the diluting effect of PαP in the iPP-rich phase is counterweighted by an increased number of nuclei that originate from the polyterpene-rich phase domains. PαP also influences the morphology of iPP spherulites, which are spherical in plain iPP and become more irregular with increasing PαP content. The number and dimension of iPP spherulites depend on blend composition and miscibility of the components. Moreover, the nonisothermal crystallization kinetics of iPP/PαP blends was analyzed with the Ozawa equation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 358–367, 2001     

Free‐radical grafting of acrylic acid onto isotactic polypropylene using styrene as a comonomer in supercritical carbon dioxide

Free‐radical grafting of acrylic acid (AAc) onto isotactic polypropylene (iPP) using styrene (St) as a comonomer in supercritical carbon dioxide (SCCO₂) medium was studied. The effects of temperature and pressure of reaction on functionalization degree (grafting degree of AAc) of the products were analyzed. The increase of reaction temperature increases the diffusion of monomers and radicals in the disperse reaction system of SCCO₂. In addition, the increase of temperature accelerates the decomposition rate of 2,2′‐azobisisobutyronitrile (AIBN), thus promoting grafting reaction. It was also observed that functionalization degree of the products decreases with the increase of pressure of SCCO₂ in the range of experiment. The effects of comonomer St on the functionalization degree of the products were investigated. The AAc graft degree of the resulting polymer was drastically higher in the present of St. It reached a maximum when the mass ratio of St and AAc was about 0.7 : 1. Because AAc is not sufficiently reactive toward iPP macroradicals, it would be helpful to use a second monomer that can react with them much faster than AAc. St preferentially reacts with the iPP macroradicals to form more stable styrene macroradicals, which then copolymerize with AAc to form branches. The highest functionalization degree was obtained when the AIBN was 0.75 wt %. When the initiator was used excessively, the functionalization degree decreased because of severe chain degradation of the iPP backbone. The morphologies of pure iPP and grafted iPP are different under the polarizing optical microscope. The diameter of the pure iPP spherulites is 20–38 μ and that of the grafted iPP spherulites is reduced with the increase of the functionalization degree of the products. This is proposed to be because the polar grafts formed during the reaction would have a tendency to associate in the hydrophobic PP environment. This might preserve some of the local crystalline order that existed during the reaction in the swollen iPP phase. It can be proven by a DSC cooling investigation that the crystallization temperature increased as the functionalization degree increased. This is proposed to be because the side‐chain of grafting polymer helps to bring about the heterogeneous nucleation in grafting polymer. Therefore, a large number of nuclei can emerge to a lesser supercooling degree. It can be also proven that the percent crystallization decreased as the functionalization degree increased, probably due to the grafted branches, which disrupted the regularity of the chain structure and increased the spacing between the chains. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2203–2210, 2004     

Effects of glass‐fiber content and coolant temperature on temperature and crystallinity profiles of PP melt during cooling

This investigation studied the temperature gradients and degree of crystallinity of polypropylene melt across a circular duct during the cooling process, where the coolant used was chilled water. The effects of glass‐fiber content, varying from 0 to 44 wt %, and coolant temperature, varying from 5 to 20°C, were our main interest. The results suggested that the rate of cooling of the polymer of each position across the duct was not significantly affected by the temperature of the coolant and glass‐fiber contents, although the rate of cooling was influenced by the size of the duct. The crystallization temperature and degree of crystallinity of the polymer increased with increasing glass fiber contents and the coolant temperature. These phenomena were associated with the heat transfer between the coolant and the polymer, crystallization temperature, exothermic crystallization process, and thermal properties of the polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2087–2097, 2001     

Self‐reinforcing isotactic polypropylene prepared using crystallizable solvents

A new approach to reinforce and toughen isotactic polypropylene (iPP) with improved processability is evaluated. The concept involves using a crystallizable solvent that, at process temperatures melts, is miscible with the polymer thereby reducing its process viscosity. As the polymer cools, the solvent undergoes thermally induced phase separation (TIPS) to produce crystallites that increase the modulus of the solid through reinforcement and promote an increase in impact resistance by mechanisms similar to rubber‐toughened materials. Tetrabromobisphenol‐A (TBBPA) is introduced to iPP that forms a homogeneous mixture at elevated temperature and acts as a processing aid, but undergoes phase separation and subsequent crystallization upon cooling to form rigid particles which, in turn, acts as a toughening agent at room temperature. A phase diagram constructed with Flory‐Huggins solution thermodynamics shows good agreement with the experimental results. The steady state shear viscosity decreases as TBBPA content increases for the mixtures in melt state, indicating improved processability. The decrease in viscosity enhances crystallization rate of iPP significantly, most likely due to increased diffusivity, while the structure of iPP crystals remain unchanged. Tensile tests show that as TBBPA content increases (up to 15 wt %), the yield stress decreases while elongation at break increases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of propylene–ethylene copolymers with different comonomer content on melting and crystallization behavior of polypropylene

The effect of propylene–ethylene copolymers (PEc) with different ethylene‐unit contents on melting and crystallization behaviors of isotactic‐polypropylene (iPP) were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The results show that the addition of PEc decreases significantly crystallization temperature (T_c) of iPP, but slightly affects melting temperature (T_m). With increasing the ethylene‐unit content of the propylene–ethylene copolymers, the decrease in crystallization temperature of iPP is smaller. The PLM results show that the spherulite growth rate decreases with increasing crystallization temperature for iPP and iPP/PEc blends. The higher the ethylene‐unit content of the copolymers is, the lower the spherulite growth rate (G) of iPP/PEc blends is. The influence of the PEc on nucleation rate constant (K_g) and fold surface energy (σ_e) of iPP was examined by nucleation theory of Hoffman and Lauritzen. The results show that both K_g and σ_e of iPP/PE20(80/20) and iPP/PE23(80/20) blends are higher than those of iPP, demonstrating that the overall crystallization rate of iPP/PEc blends decreased as compared to that of iPP, resulting from the decrease of the nucleation rate and the spherulite growth rate of iPP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of nucleating agent addition on crystallization of isotactic polypropylene

The isothermal and nonisothermal crystallization kinetics of nonnucleated and nucleated isotactic polypropylene (iPP) were investigated by DSC and a polarized light microscope with a hot stage. Dibenzylidene sorbitol (DBS) was used as a nucleating agent. It was found that the crystallization rate increased with the addition of DBS. The influence of DBS on fold surface energy, σ_e, was examined by the Hoffman and Lauritzen nucleation theory. It showed that σ_e decreased with the addition of DBS, suggesting that DBS is an effective nucleating agent for iPP. Ozawa's theory was used to study the nonisothermal crystallization. It was found that the crystallization temperature for the nucleated iPP was higher than that for nonnucleated iPP. The addition of DBS reduced the Ozawa exponent, suggesting a change in spherulite morphology. The cooling crystallization function has a negative exponent on the crystallization temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2089–2095, 1998     

Polymer crystallization kinetics,master quotients,master curves and Nakamura‐Ozawa‐equations of iPP and PTFE

Evaluation concepts related to Avrami master curves are described for the analysis of isothermal and non‐isothermal kinetic processes exhibiting topological nucleation and growth characteristics. These evaluation concepts are shown to be helpful for studies focusing on kinetic data of polymer crystallization experiments with iPP (isotactic polypropylene) and PTFE (polytetrafluoroethylene). An apparent m‐order reaction model is discussed with respect to the isokinetic nucleation and growth model of Nakamura as well as to the non‐isothermal crystallization kinetics theory of Ozawa. Thus, the cooling functions χ(T) of iPP and PTFE, obtained by analyzing DSC (differential scanning calorimetry) experiments with constant cooling rates, are calculated in two alternative ways by using clearly different mathematical approaches. Finally, master quotients, theoretical crystallization limits, and further types of master curves are defined. Polym. Eng. Sci. 44:2194–2202, 2004. © 2004 Society of Plastics Engineers.     

Synthesis and kinetic behavior of stereotriblock polybutadiene using dilithium as initiator

Anionic polymerization of butadiene was conducted in cyclohexane using 1,1,4,4‐tetraphenyl‐1,4‐dilithium butane (TPB–DiLi) as initiator and dipiperidinoethane (DPE) as modifier. The polymer design effects of DPE/TPB–DiLi (simplified as DPE/Li) and polymerization temperature on the 1,2 content of polybutadiene (PB) were examined and 1,2‐polybutadiene (1,2‐PB) with a nearly 100% 1,2 content was obtained. 1,2–1,4–1,2‐Stereotriblock polybutadiene (STPB) can be synthesized easily by means of one feed reaction. DSC and DMA analyses showed that STPB with the designed molecular structure (molecular weight, block ratio, and 1,2 content in 1,2 blocks) has two T_g's and two loss moduli and exhibits microphase separation. Studies on reaction kinetics established the polymerization kinetics equation of 1,4‐PB as ?d[M]/dt = 0.356[C]^0.5[M], indicating the first‐order relationship between polymerization rate and monomer concentration. At 50°C, the addition of the strong polar modifier DPE into the system increased the reaction rate. The apparent propagating activating energies before and after DPE addition were also determined in this study. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1049–1054, 2003     

A novel highly efficient β‐nucleating agent for polypropylene using nano‐CaCO3 as a support

In order to increase the isotactic content of β‐nucleated polypropylene (β‐iPP) and decrease the cost of its production, the investigation and development of novel highly efficient β‐nucleators are important issues. Nano‐CaCO₃ was used as a support to prepare a supported β‐nucleator, nano‐CaCO₃‐supported calcium pimelate. Fourier transform infrared spectral analysis shows that an in situ chemical reaction takes place between nano‐CaCO₃ and pimelic acid. Differential scanning calorimetry results indicate that the crystallization and melting temperatures of β‐phase in supported β‐nucleator‐nucleated iPP are higher than those of calcium pimelate‐nucleated iPP. The β‐nucleating ability of the supported β‐nucleator is little influenced by the cooling rate and crystallization temperature over a wide range. The decreased content of pimelic acid in the supported β‐nucleator slightly decreases the crystallization temperature of iPP but it has no influence on the content of β‐phase in nucleated iPP. A novel supported β‐nucleator has been successfully synthesized via pimelic acid supported on the surface of CaCO₃. The crystallization temperature of iPP and melting temperature of β‐phase in iPP nucleated using the supported β‐nucleator are higher than those of iPP nucleated using calcium pimelate. The concept of a supported nucleator will provide a new way to increase the efficiency of polymer additives and to decrease the amounts of them that need to be used by using nanoparticles as supports. Copyright © 2010 Society of Chemical Industry     

Influence of the amount of salts of rosin acid on the nonisothermal crystallization,morphology, and properties of isotactic polypropylene

The nonisothermal crystallization of Isotactic polypropylene (iPP) containing different concentration of nucleating agent potassium dehydroabietate (DHAA‐K) or sodium dehydroabietate (DHAA‐Na) at the cooling rate of 10°C/min was investigated using differential scanning calorimetry (DSC) together with Jeziorny's method. It was found that the temperature at which the maximum rate of crystallization occurred shifted to a higher region by about 13.7–16.9°C, and the rate of crystallization became faster for iPP with DHAA‐K (PPK) or DHAA‐Na (PPNa) in comparison to the virgin iPP. Avrami exponent for virgin PP, PPK, and PPNa was about 3.1, 2.2, and 2.2, respectively, suggesting the change of the crystal growth mechanism of iPP with the addition of the nucleating agents. The morphology of iPP with and without nucleating agent examined by a cross polarized light microscope indicated that the size of spherulites marginally decreased, which then remained stable with the increase of the concentration of DHAA‐K or DHAA‐Na. The measurements of the optical and mechanical properties of iPP showed that the transparency, gloss, and flexural modulus increased with increasing nucleating agent before its optimal concentration. POLYM. ENG. SCI., 47:889–897, 2007. © 2007 Society of Plastics Engineers