High Molecular Weight Polypropylene Research Articles

Dynamic behavior of melt electrospinning of blended polypropylene

Melt electrospinning is a promising process for fiber production without the need for solvents and with potential applications in various fields. In this study, we investigated the dynamic behavior of melt electrospinning under different blending ratios and process conditions. We used high melt flow index polypropylene and low molecular weight polypropylene, which were blended to lower the melt viscosity, and fibers were successfully manufactured through the melt electrospinning process. The effects of blending ratio and applied voltage on jet and drop formation, as well as fiber morphology, were examined. The results showed that blending low-molecular-weight polypropylene significantly influenced the jet and drop areas, leading to fluctuations in jet morphology. The size of the applied high voltage also had a high effect on the fiber diameter. Additionally, the viscosity reduction achieved through blending allowed for continuous jet formation and improved fiber production. These results provide valuable insights into controlling the process parameters and blending ratios in melt electrospinning, enabling the establishment of stable electrospinning conditions and precise control of fiber diameter.

A hybrid steric ligand modification strategy promotes propylene (co)polymerization

Recently, a Hybrid Steric Ligand Modification (HSLM) strategy has been shown to significantly increase the polymerization activity and the branching degree of the resulting (co)polymers in the ethylene (co)polymerization via α-diimine catalysts. In this study, the HSLM strategy was employed for propylene (co)polymerization using a group of α-diimine Pd(II) catalysts with bulky hybrid ligands. The HSLM catalysts (Pd1-4) produced polypropylene with high molecular weights (45.4–156.9 kg/mol) and resulted in significantly high levels of activity (105 g mol−1 h−1). Additionally, nearly half of the propylene underwent chain straightening (1,3-enchainment = 43–46 %). Our findings suggest that Pd1-4 catalysts are more effective than the symmetrical catalysts Pd5-6 in producing high molecular weight polypropylene with high activity. Among all the catalysts tested, Pd4 with 4-tert-butylphenyl displayed the highest polymerization activity and molecular weight, although with lowest branching densities. It is suggested that the HSLM may provide a more open spatial configuration around the metal center, which facilitates the coordination and insertion of propylene molecules as well as chain walking. The hybrid Pd(II) catalysts showed moderate activity during the copolymerization of propylene with MA. The copolymers produced had low molecular weights (3.1–11.2 kg/mol), high branching densities (120–211/1000C), and high incorporation ratios (8.82–18.08 mol%). The copolymerization activity was highest with 4-tert-butylphenyl Pd4. The resulting P-MA copolymers had the highest molecular weight, the largest branching degree, and the lowest incorporation ratios.

Mold temperature- and molar mass-dependent structural formation in micro-injection molding of isotactic polypropylene

The structural formation and development of isotactic polypropylene (iPP) upon the micro-injection molding process was investigated at different mold temperatures and molecular weights utilizing a real-time synchrotron radiation small angle X-ray scattering (SAXS) technique combined with a customized micro-injection molding apparatus. Shish-kebab structure and parent-daughter lamellae were found to be formed during micro-injection molding for all iPP samples. In the case of kebab lamellae, a considerable growth in the long period and in the average thickness of lamellar crystallites and amorphous domains is observed at initial stages of crystallization for samples molded at varying temperatures. This effect is caused by the successive formation of thin lamellae in the outer layer and thick lamellae in the inner layer during the manufacturing process as evidenced by the spatial distribution of the crystalline lamellae across the thickness. In addition, the length of the shish formation increases remarkably at the onset of crystallization, the extent of which is dependent on the mold temperature. Despite the large changes of the lamellar stacks and the shish misorientation, the final length of the shish remains essentially unchanged when varying mold temperature. Since there is a critical orientation molecular weight above which the chains are stretched and oriented to form stable shish, the iPP sample with a low molar mass exhibits an overall decrease in the scattering intensity of SAXS patterns compared to the high molecular weight polypropylene. • The structural formation of iPP is investigated utilizing a customized micro-injection molding device. • Shish-kebab and parent-daughter lamellae are formed during micro-injection molding. • A considerable increase in the long period is observed at initial stages of crystallization. • The length of the shish formation increases remarkably at the onset of crystallization. • The final shish length remains essentially unchanged when varying mold temperature.

Substituent Effects of Phenyl Group on Silylene Bridge in Stereospecific Polymerization of Propylene with C₁-Symmetric Ansa-Silylene(fluorenyl)(amido) Dimethyl Titanium Complexes.

A C1-symmetric (methylphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (1) and (diphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (2) were synthesized and characterized by 1H NMR, element analysis, and X-ray crystal analysis. The coordination mode of the fluorenyl ligand to the titanium metal is an η3 manner in each complex. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst under different propylene pressures in a semi batch-type method. The catalytic activity was strongly dependent on the structure of the complex and the propylene pressure, where complex 1 exhibited the highest activity (600 kg mol−1·h−1) under a propylene pressure of 8.0 atm to produce high molecular weight polypropylene. The polypropylenes obtained were syndiotactic-rich with an rr value of 0.50, indicating that the silylene bridge was not efficient for the isospecificity of a constrained geometry catalyst (CGC). The mechanical properties of the resulting polymers depended on their microstructure.

In-situ cooling of adsorbed water to control cellular structure of polypropylene composite foam during CO2 batch foaming process

The fixation stage of cellular structure during polymer foaming process is difficult to control due to difficult removing of internal heat, especially for crystalline polymers such as polypropylene (PP). In order to control cellular structure in the fixation stage, we established an universal method by introducing water as an in-situ internal cooling agent during the foaming process of PP. Particularly, hydrophilic fillers were added into the high melt flow index polypropylene (HMI-PP) with poor foaming ability to study the effect of adsorbed water on the foaming process of PP/filler composites during sc-CO2 batch foaming process. Compared to pure HMI-PP, HMI-PP/hydrophilic filler composites showed increased adsorption amount for water and melt viscosity. The water within the composites played a key role in the foaming process, which not only served as a physical foaming agent to increase the volume expansion ratio of PP composite foam, but also showed the function of rapid cooling foam proved by thermal imaging technology. As a result, the presence of some hydrophilic fillers within HMI-PP matrix significantly improved the foaming properties of HMI-PP, including preventing internal bubble collapse and significantly increasing the volume expansion ratio of the foam. The applicability of this method was validated using other PP materials besides HMI-PP, including high molecular weight PP (HMW-PP), high melt strength PP (HMS-PP).

Isolation of mesophilic bacterium for biodegradation of polypropylene

A mesophilic bacterium capable of polypropylene (PP) biodegradation was isolated from soil using a culture medium containing low molecular weight polypropylene (LMWPP) as a carbon source. The biodegradation of LMWPP and high molecular weight polypropylene (HMWPP), by the isolated bacterium, was measured under compost conditions. As produced PP has a broad molecular weight distribution so that it contains molecules with a wide spectrum of chain length, ranging from extremely low molecular weight to very high molecular weight. As the extremely low molecular weight fraction of PP may produce misleading results on biodegradability of PP, Soxhlet extraction using toluene was performed to obtain HMWPP, by dissolving out the extremely low molecular weight fractions from PP as produced from a commercial scale polymerization reactor. Previous research on PP biodegradation used PP compounded with pro-oxidants or with natural polymers, such as starch, or pretreated commercial-grade PP containing various additives, such as heat and light stabilizers. In contrast, the present study employed PP without any additives, to examine the true biodegradability of neat PP, excluding any effects of the additives.

Synthesis of C1 symmetrical ansa-cyclopentadienylamidotitanium complexes and their application for living polymerization of propylene

Optically active C1 symmetrical [(R)-NCHMe(Naphthyl)SiMe2Flu]TiMe2 (1) and [(R)-NCHMe(Naphthyl)SiMe2(C5Me4)]TiMe2 (2) were synthesized and characterized by elemental analysis, 1H NMR and single crystal X-ray analysis. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst at 0 °C in toluene, heptane and chlorobenzene, respectively. All the systems showed steady polymerization rate and gave high molecular weight polypropylene with narrow molecular weight distribution, and the toluene system showed higher activity than the heptane system. The postpolymerization testified that each catalytic system conducted the propylene polymerization in a living manner. The 2-chlorobenzene system showed fastest propagation rate of 437 mol min−1. The polymers produced with the 1-heptane and -toluene systems or 2-heptane system were statistically atactic, while the polymers produced with the 2-toluene system were isotactic-rich PP with isotactic triad (mm) of 0.61.

Unravelling the contribution of chain microstructure in the mechanism of the syndiotactic polypropylene pyrolysis

The pyrolysis of a highly syndiotactic and high-molecular weight polypropylene (sPP) has been thoroughly studied through preparative TGA experiments, which were performed up to final temperatures between 262 °C and 427 °C. The 13C NMR characterization of the samples shows a two-stage process clearly evidenced by changes in the chain microstructure. In a first period, up to a 22% weight loss, the molecular weight collapses and only vinylidene end-capped chains are produced. In a second stage, over 22% weight loss, a wider variety of groups, including both terminal vinylen and isobutenyl functions as well as n-propyl tails, are also detected. Regardless the type, all these new species are formed at the expense of propylene units belonging to rrrr pentads.The evolution of the Eact predicted by means of analytical TGA allows us to associate the lowest Eact value found with the changes taking place during the very beginning of the process (up to a 3% weight loss), i.e. the molecular weight collapse and a some evidence of configurational stereo-specificity. As regards the further Eact build-up, it can be rationalized in terms of the ability of chains to be rolled in the most stable GGTT conformation, as it is supported by complementary FTIR and DSC characterization of the samples.

Polypropylene-elastomer (TPO) nanocomposites: 2. Room temperature Izod impact strength and tensile properties

Room temperature Izod impact strength was determined for polypropylene (PP)/ethylene-co-octene elastomer (EOR) blends and nanocomposites, containing organoclays based on montmorillonite (MMT), at fixed elastomer content of 30 wt% and 0–7 wt% MMT. A ratio of maleated polypropylene, PP-g-MA to organoclay of unity was used as a compatibilizer in the nanocomposites. The organoclay serves to reduce the size of the EOR dispersed phase particles and facilitates toughening. The Izod impact strength is also influenced by the molecular weight of PP, elastomer octene content, elastomer MFI in addition to MMT content. Nanocomposites based on a low molecular weight polypropylene (L-PP) containing a higher octene content elastomer showed higher impact strength at lower MMT contents compared to those based on a low octene content elastomer. The effect of elastomer octene content on impact strength of high molecular weight polypropylene (H-PP) nanocomposites is not so significant. Elastomers having a melt flow index (MFI) in the range of 0.5–1.0 showed significant improvement in the impact strength of L-PP based nanocomposites. Most H-PP/EOR blends gave ‘super-tough’ materials without MMT and maintain this toughness in the presence of MMT. The critical elastomer particle size below which the toughness is observed is reduced by decreasing the octene content of the elastomer. For the similar elastomer particle sizes in nanocomposites, the impact strength varies as H-PP > M-PP > L-PP. The tensile modulus and yield strength improved with increasing MMT content; however, elongation at break was reduced. The extruder-made TPO showed a good-balance of properties in the presence of MMT compared to reactor-made TPO having similar modulus and elastomer content.

Polypropylene-elastomer (TPO) nanocomposites: 1. Morphology

PP/PP-g-MA/MMT/elastomer nanocomposites were prepared in a twin-screw extruder at fixed 30 wt% elastomer and 0–7 wt% MMT content. The ratio of maleated polypropylene, PP-g-MA and organoclay was maintained at 1. Elastomer particle size and shape in the presence of MMT were evaluated for three different molecular weight grades of polypropylene (PP) and five different ethylene-co-octene elastomers (EOR) with different melt flow index (MFI) and octene contents. The MMT particles are located exclusively in the PP phase in the PP/PP-g-MA/MMT/EOR nanocomposites as seen from TEM images. Injection molded nanocomposite samples show significant decreases in elastomer particle size and increases in elastomer aspect ratio and particle density compared to as-extruded or pelletized samples. The elastomer particle size decreased significantly with increased MMT content and the molecular weight of PP. Low molecular weight PP based nanocomposite showed a greater reduction in elastomer particle size compared to medium and high molecular weight PP based nanocomposites. Elastomers having MFI in the range of 0.5–1.0 gave minimum elastomer particle sizes in the PP/PP-g-MA/MMT/EOR nanocomposite. The elastomer particles were deformed during injection molding leading to an increase in their aspect ratio. The nanocomposites containing high octene content elastomer gave smaller elastomer particle size and higher elastomer aspect ratios compared to nanocomposites containing low octene content elastomer.

Classification of acoustic emission signals collected during tensile tests on unidirectional ultra high molecular weight polypropylene fiber reinforced epoxy composites using principal component analysis

The objective of this study is to utilize a mathematical procedure for the evaluation of damage mechanism in ultra high molecular weight polypropylene/epoxy composite (UHMWPP/epoxy) specimen with different configuration based on the analysis of the AE signals of presented. Principal component analysis (PCA) is powerful tool, which utilized for the classification of the monitored AE transients. We worked on epoxy L160 resin, UHMWPP fiber bundle and UHMWPP/epoxy unidirectional specimens, subjected to tensile loading. Using model specimens exhibiting a predominant damage mechanism, correlations were established between the observed damage growth mechanisms and the AE parameter variances result in PCA. Outputs from this study revealed that the PCA is an effective tool for identifying damage modes such as matrix cracking, fibre/matrix debonding, fibre breakage and fibre pull-out in the UHMWPP/epoxy composites. The presence of damage modes in UHMWPP/epoxy composites was proven with scanning electron microscopy (SEM) images.

Effects of coating amount and particle concentration on the impact toughness of polypropylene/CaCO3 nanocomposites

The effects of the coating amount of surfactant and the particle concentration on the impact strength of polypropylene (PP)/CaCO3 nanocomposites were investigated. Nanocomposites prepared with monolayer-coated CaCO3 nanoparticles had the best mechanical properties, including Young’s modulus, tensile yield stress and impact strength because of the good dispersion of the nanoparticles in the polymer matrix. In addition, the good dispersibility of the monolayer-coated nanoparticles allowed us to study the effects of particle concentration on the impact strength of the nanocomposites. H-PP and E-PP, which were the low and high molecular weight PPs, respectively, were used as polymer matrices. Critical particle concentrations of 10 and 25wt% corresponding to an abrupt increase in the impact toughness were determined for the E-PP and H-PP nanocomposites, respectively. Good particle dispersion in a polymer matrix is the prerequisite for the calculation of the critical ligament thickness using the critical particle concentration. We propose that the observed critical ligament thickness actually corresponds to the critical thickness at which the plane-strain to plane-stress transition occurs. In addition, the critical ligament thickness of a nanocomposite depends on the properties of the polymer matrix, such as molecular weight, even for a given type of polymer.

Exfoliation of clay layers in polypropylene matrix using potassium succinate-g-polypropylene as compatibilizer

The efficiency of potassium succinate-g-polypropylene (KPPSA) as compatibilizer for the dispersion of clay in a high molecular weight polypropylene during melt mixing for the preparation of nanocomposites was evaluated and compared with maleic anhydride-g-polypropylene (PPMA). Nanocomposites were prepared by direct melt mixing and by masterbatch methods and the structure obtained was characterized by WAXD and TEM. The exfoliation and better dispersion of the organoclay was observed with KPPSA than PPMA. The dispersion of clay was found to be dependent on the method of preparation, type and the amount of compatibilizer used. The dispersion was better when the nanocomposites were prepared by two step masterbatch route than the single step direct mixing method. Flexural moduli and crystallization behavior were studied and correlated with the dispersion of organoclay in the PP matrix.

Stereospecific Octahedral Group 4 Bis(phenolate) Ether Complexes for Olefin Polymerization

Octahedral group 4 bisphenolate ether complexes, activated by methylaluminoxane, are highly active and stereospecific alpha-olefin polymerization catalysts. X-ray crystallographic analysis reveals the Zr and Hf complexes to be closely isostructural; the bond lengths of the Hf complex are slightly shorter, but the maximum deviation is only 0.062 A. Despite the structural similarity of the Hf and Zr complexes, the Hf complexes generate more highly stereoselective catalysts. In addition to the influence of the transition metal, the structure of the ligand has a large influence on the stereospecificity. Bis-tert-butyl phenyl substituted complexes of Hf and Zr, when activated by MAO at 50-80 degrees C, generate high molecular weight polypropylene (M(n) = 130,000-360,000 g/mol) with isotacticities [mmmm] > 97% and melting points as high as 165 degrees C.

Synthesis of polypropylene with varied microstructure and molecular weights characteristics using supported titanium catalyst system

Propylene polymerizations were conducted in slurry phase batch process using different dialkyldimethoxysilanes as an external donor with magnesium dichloride (MgCl2) supported titanium tetrachloride (TiCl4) catalyst having diisobutylphthalate (DIBP) as an internal donor. The dialkyl group of the external donors like dimethyldimethoxysilane (DMDMS), diisopropyldimethoxysilane (DIPDMS) and dicyclopentyldimethoxysilane (DCPDMS) were found to influence on the microstructure and the molecular weight characteristics of synthesized polypropylene in addition to the initial rate of polymerization and decay index. DCPDMS gave highest productivity and high molecular weight polypropylene with improved kinetics while DMDMS gave lowest productivity in comparison. The molar equivalent combination of DCPDMS with DIPDMS and DMDMS respectively, resulted in producing polypropylene with tacticity pattern and molecular weight characteristics in between the individual alkoxysilane based system indicating the effect of alkyl group on the catalyst performance.

Polypropylene nanosphere: particle size and crystal structure

The high molecular weight polypropylene (PP) nanospheres (average particles size ∼ 60 nm) were synthesized under controlled growth condition using Ziegler-Natta catalyst. The sizes of the PP particles were investigated through microscopy analysis. The size-dependent crystal structure and crystallinity were studied through X-Ray powder diffraction (XRD) and differential scanning calorimetry (DSC). At 25°C PP nanoparticles show higher crystallinity (∼76%) compared to the micron sized PP particles (∼59%). The rearrangement of polymer chains is the reason for the higher crystallinity of nanosphere PP particles. The periodic organization of PP chains inside the nanoparticles shows new peaks. These corroborate the presence of α-monoclinic phase. The α-crystalline lamella lengths of various particle sizes are calculated and found to be 14.5 nm for nanoparticles, whereas the same for the microsphere PP is 17.6 nm. The crystal domains consist of various sizes of α-monoclinic crystals. Moreover, the absence of γ-orthorhombic phase acknowledges that the PP nanospheres are composed of α-monoclinic crystal domains.

High molecular weight polypropylene nanospheres: Synthesis and characterization

AbstractThe high molecular weight (MW) polypropylene with average particle size of 60 nm was synthesized by controlled growth mechanism using Ziegler–Natta catalyst. The atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies showed that PP nanoparticles were spherical in shape. Structure and crystallinity were concomitantly studied through Fourier transform infrared spectroscopy and X‐ray diffraction, respectively. It shows nanospherical PP particles with more crystallinity (∼ 75%) compared with macrosized PP (∼ 59%). In addition, differential scanning calorimetry studies revealed the finite particle size effect on Tg and the scale dependence Tg followed a first order exponential trend. As particle size goes down to nano‐ scale from macrosize, continuous elevation of Tg's were observed from −25 to −11°C. This phenomenon was directed to configuration entropy of single spherical nanoparticles of PP. The mechanical properties and surface roughness were also evaluated through AFM. At last, the properties of nanosized PP were compared with micron and macrosized particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effects to Improve the Quality of Life: Color, Performance and Protection from Ciba Specialty Chemicals

Ciba Specialty Chemicals creates effects to improve the quality of life. Building on its technical competencies, the company has developed major innovative product groups that provide color, performance and protection. Antioxidants and light stabilizers protect plastics, coatings, photographic pictures and wood from degradation induced by sunlight, air, ozone, heat, fire and mechanical stress. UV absorbers protect human skin from sunburn and photo-induced ageing. Pigments and dyes add beautiful colors to objects of everyday life, serve as recording media for optical information storage on digital versatile discs (DVDs) and are used as color filters in liquid crystal displays (LCDs). Effect pigments allow creation of color and visual effects by interference. Polymeric flocculants are essential components for solid–liquid separation processes in wastewater treatment and paper production. Photolatent catalysts are key components for light-induced polymerization reactions. New sterically hindered N-alkoxyamines are initiators for nitroxide mediated radical polymerization (NMP) reactions leading to new pigment dispersants with well-defined molecular weights and narrow molecular weight distribution. New N-acyloxyamines are proposed as peroxide substitutes for controlled degradation of high molecular weight polypropylene. A new clarifier can be used to produce polypropylene with enhanced transparency and excellent mechanical properties. Progress in enabling sciences such as nanotechnology and biotechnology together with new technologies entering the markets will offer outstanding opportunities for new developments in specialty chemicals.

In situ Polypropylene Nanocomposites: Gas‐Phase Polymerization of Propylene in the Presence of Nanofillers using Nanosilica‐Supported‐Zirconocene Catalyst

This work concentrates on using the gas‐phase polymerization technique for the production of highly loaded nanocomposites. Filler loading levels near the vicinity of 40 wt% have been obtained using different nanofillers. Three different in situ Polypropylene (PP) nanocomposites, i.e., Cloisite‐20A filled polypropylene (CFPP), Kaolin filled polypropylene (KFPP) and nanosilica filled polypropylene (SFPP) have been prepared by gas‐phase polymerization. The catalyst used is Nanosilica‐Supported‐Zirconocene. The fillers used are Closite‐20A, Kaolin and nanosilica, respectively. These were pre‐treated with MAO (Methylaluminoxane) to inhibit their deactivating action on the catalyst because of the presence of either acidic or basic groups on their surfaces; in this way MAO acts as a co‐catalyst for the three polymerization reactions being discussed. Significantly higher molecular weight polypropylene was formed with nanosilica as the filler. The melting temperature and enthalpy is also observed to be comparatively higher in this case. However, in the case of other fillers, the molecular weights, as well as melting points, are comparatively lower. With the catalyst used, a mixture of crystalline and amorphous polypropylene was observed to form. Comparatively lesser amounts of crystalline polypropylene are also observed.

Metallocene-mediated synthesis of chain-end functionalized polypropylene and application in PP/clay nanocomposites

This paper summarizes our research in the preparation of chain end functionalized isotactic polypropylene (PP) having a terminal functional group, such as Cl, OH, and NH 2. The chemistry involves metallocene-mediated propylene polymerization using rac-Me 2Si[2-Me-4-Ph(Ind)] 2ZrCl 2/MAO complex in the presence of styrene derivatives (St-f) and hydrogen, which serve as the chain transfer agents. The molecular weight of the resulting PP polymers with a terminal Cl, OH and NH 2 group (i.e., PP-t-Cl, PP-t-OH and PP-t-NH 2) are inversely proportional to the molar ratio of [St-f]/[propylene]. Despite the extremely low concentration of functional group, the high molecular weight chain end functionalized PP-t-OH and PP - t - NH 3 + exhibit a distinctive advantage over other functional PP polymers containing side chain functional groups or long functional blocks. The terminal hydrophilic OH and NH 3 + cations, with good mobility and reactivity, effectively hydrogen bond and ion-exchange the cations (Li +, Na +, etc.) located between the clay interlayers, respectively. Such interactions anchor the PP chain to the clay surfaces. On the other hand, the remaining rest of the unperturbed end-tethered high molecular weight PP tail exfoliates the clay layers. This exfoliated structure is maintained even after further mixing of the PP-bearing platelets with pure neat PP polymers.