Weight Polypropylene Research Articles

Incisional hernia in patients at risk: can it be prevented?

Incisional hernia is a long-term complication of laparotomy. Its exact frequency varies according to different authors, but is always around 10-15%. There are patients who present with systemic associated diseases [chronic obstructive pulmonary disease (COPD), obesity, severe cardiopathies, immunodeficiencies, etc.] that favour or increase the risk of appearance of an incisional hernia. The aim of the present study was to assess whether the prophylactic placement of a polypropylene mesh in patients at risk can reduce or avoid the appearance of an incisional hernia. Seventy-two selected patients with clear risk factors and colon pathology underwent surgical intervention through median infraumbilical laparotomy. During laparotomy the preperitoneal space was dissected at a point where a low-molecular weight polypropylene mesh was to be placed when closing the peritoneum. Meshes were about 7-8 cm wide and had a variable length that depended on the length of the surgical incision. Of the 72 patients, 41 were obese (BMI > 30 kg/m(2)), 45 presented with COPD, and 42 with colorectal neoplasia; 29 patients had two risk factors, and 15 had three risk factors. The mesh was held in place with polypropylene stitches in 28% of cases, and with fibrin glue in 72% of cases. All patients were assessed by a protocol that included interview, examination of the surgical wound, and abdominal CT scan. Follow-up was between 3 and 5 years. There were no noteworthy complications or operative mortality. No mesh had to be removed in any patient. Two patients developed liver metastasis, and in a second surgery the good condition of the abdominal wall and the absence of hernia were confirmed. Twenty patients required postoperative chemotherapy. Two patients died at 37 and 43 months after surgery because of progression of the neoplastic disease. Fourteen patients were monitored for more than 5 years after surgery, and 46 patients were monitored for 48 months. None of the 72 patients developed an incisional hernia. Prophylactic use of a low-molecular-weight polypropylene mesh in abdominal surgery may be useful for the prevention of incisional hernia.

Broad Molecular Weight Polypropylene Synthesis using Mixed Internal Donor Incorporated Magnesium Dichloride Supported Titanium Catalyst

Magnesium dichloride supported titanium tetrachloride catalyst with mixed internal donor, comprised of ethylbenzoate and sulfolane, were synthesized. The composition characteristics of catalysts indicate incorporation of sulfolane to max 8.2 wt%, in addition to ethylbenzoate. The amount of incorporated donors in solid catalyst is dependent on the sulfolane concentration and reaction temperature of the process. A physical characteristics study of catalyst indicated that morphology, crystallite size, surface area, pore volume and titanium distribution have not been influenced much by incorporation of the second internal donor (sulfolane). The catalysts, in combination with triethyl aluminum as cocatalyst and p-ethoxyethylbenzoate as external donor, show good activity for propylene polymerization. The polypropylene synthesized with an optimized catalyst system shows broad molecular weight distribution as compared to ethylbenzoate based catalyst.

Magnetic fluids stabilized by polypropylene glycol

A series of samples of magnetic fluids stabilized with low-molecular weight polypropylene glycol (PPG) of different molecular masses were synthesized. The use of PPG allowed the maximum extension of the carrier fluid range to include ethyl- and butyl-acetate, ethanol, butanol, acetone, carbon tetrachloride, toluene, kerosene and PPG itself. Magnetic and rheological properties of the samples were investigated. Based on the results of investigation it has been concluded that magnetic nanoparticles are covered by a monolayer of surfactant molecules. At low temperatures the propanol-based sample preserves fluidity up to −115 °C. Measurement of critical temperatures of other base fluids showed that alcohols are the best carrier medium. Coagulation stability of the ethanol-based ferrocolloid with respect to water and kerosene was explored. It has been found that kerosene, whose fraction by weight exceeds 22.5%, does not mix with the colloid. This effect can be used to produce magneto-controllable extractors of ethyl alcohol. Under the action of water the colloid coagulates, which allows one to substitute the carrier fluid and to separate the colloid into fractions.

Effect of polypropylene molecular weight, hydroxyapatite particle size, and Ringer’s solution on creep and impact behavior of polypropylene-surface treated hydroxyapatite biocomposites

In this study, bovine bone was burnt at 400°C and the resulting ash was heat-treated at 900°C for 90 min to get a white powder. Chemical analysis showed that this white powder was mainly hydroxyapatite (HA). Three different average particle sizes of this powder were produced by milling at three different times. The produced HA was surface treated with a silane coupling agent. Composite samples with 40 vol.% of HA were produced by hot press molding and so mechanical testing was done on the specimens in air and Ringer’s solution. The results of these tests showed that on increasing the molecular weight of polypropylene (PP), creep strain of composites decreases proportionally, and ultimate tensile strength (UTS) and impact resistance increase dramatically. In addition, result of mechanical tests on the soaking specimens in Ringer’s solution showed that Ringer’s solution intensively decreases UTS, creep, and impact properties of PP—HA composite. Furthermore, decreasing HA particle size caused UTS rise, creep strain fall, and impact resistance rise for composites in air condition. Vice versa, in wet condition, decreasing HA particle size caused UTS, creep, and impact resistance to fall. Fracture surfaces of impact samples tests were analyzed by a scanning electron microscope.

Novel stable MDI isocyanate-based bituminous foams

Foam building materials are used in roofing and water proofing membranes, insulation, pipe covers, vapour barriers, crack suppressant membranes, and as installed flooring protection. In this study, new stable bituminous foams have been developed, in a two-step method, using a reactive polymer, synthesized from the reaction of 4,4′-diphenylmethane diisocyanate with a low molecular weight polypropylene glycol (MDI–PPG). Firstly, a modified bitumen was obtained by adding 10 wt.% MDI–PPG to bitumen, at 90 °C. In a second step, an excess of water was added, which reacted with the remaining –NCO groups and generating CO 2, which was used as a chemical foaming agent to produce stable bituminous foams. In general, polymer addition improves the bituminous foam rheological properties, mainly in the high in-service temperature region. In this range of temperature, the rheological properties are clearly affected by reaction time.

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.

Novel bitumen/isocyanate-based reactive polymer formulations for the paving industry

Reactive modification is lately gaining acceptance as a successful way to give added value to bitumen, a crude oil refining by-product. In order to study the effect of both bitumen type and processing method, isocyanate-based reactive modification was carried out with four types of bitumen from different sources, by following two different procedures (“water-free” and “water-involved” processing). The polymer used (MDI–PPG) was synthesized from the reaction of 4,4′-diphenylmethane diisocyanate with a low molecular weight polypropylene glycol. The results obtained demonstrate that the addition of small quantities of this reactive polymer to bitumen endows the resulting modified binder with an improved performance at high in-service temperatures. Interestingly, two different modification pathways have been identified: the first one, which occurs during mixing, is the result of chemical reactions between -NCO groups of the reactive polymer with functional groups containing active hydrogen atoms (mainly, –OH), such as those typically present in the most polar bitumen fractions; the second one has been proved to be a consequence of series reactions involving water. Both pathways, but mainly the latter, lead to bituminous paving materials showing a more complex microstructure, with the consequent change in their rheological response. Finally, very different degrees of modification, depending on the colloidal features of the as-received bitumen, were observed.

Effects of Molecular Weight of Polypropylene on the Correlation between Fracture Toughness and Mechanical/Impact Properties of Gfpp Composites

The accurate prediction of scientific and statistical parameters depends, largely, on the functional correlation between the variables involved, as well as their definite and predictable behaviour around the line of best fit (the regression line). Hence, an accurate and reliable prediction of the fracture toughness and mechanical properties of glass fibre reinforced polypropylene (GFPP) composites is very important in order to prevent sudden failure of components fabricated from them. It also gives the opportunity to save cost on experimentation. Three grades of polypropylene (PP) of different molecular weights (MW) had glass fibre reinforcements each. The incorporation of maleic anhydride grafted PP (MA-g-PP) into the composites was for compatibilisation between the matrix and reinforcements. There was tensile testing on both the un-notched and notched dumbbell samples. The use of J-Integral analysis was to investigate the fracture toughness of the composites. There was an evaluation of the effect of different MW of PP on the fracture toughness and impact properties of the composites. The examination of the morphology of the materials was by (SEM), while charge coupled device (CCD) camera monitored crack propagation behaviour under tensile loading. There was further morphology study to analyse the fibre length distribution and interfacial shear strength of the composites. Investigations revealed that the composite with the lowest MW PP consistently showed better mechanical, impact and fracture toughness properties than those with higher MW PP. It was also observed that incorporating MA-g-PP as compatibilisers had greater interfacial bonding effects, resulting in higher interfacial shear strength in GFPP of lower MW and high melt flow rates than those of higher MW and low melt flow rate. The investigation further revealed that as the MW of PP decreased, the fracture toughness and other mechanical properties increased in a linear correlation. Crack propagation trailed the interface between PP matrix and GF because of weak bonding in the composite with higher MW PP. This study revealed that incorporating MA-g-PP into GFPP composites achieved better properties with PP of lower MW and higher melt flow rate. Hence the mechanical and fracture properties of GFPP depend largely on the MW of the polymer PP matrix. There was a strong linear correlation observed between the MW of PP, fracture toughness and other impact properties thereby making it possible to make a reliable prediction of any property of the composites from another.

Mesh Augmentation of Posterior Repair – A Safe, Cost Effective Approach

Study Objective: To determine if mesh augmentation during a posterior repair can be safely performed with custom shaping of an ultra-low molecular weight polypropylene mesh without the use of a commercial kit.

Mechanical evaluation of synthetic biomaterials used in the correction of pelvic floor disorders—Experimental study in rabbits

Objective To evaluate the biomechanical properties of the principal prosthetic materials currently used in genital prolapse surgery. Study design Based on an animal model of incisional abdominal hernia, 40 adult rabbits were implanted. Four 2.5 cm × 2.5 cm parietal defects, were created in the abdominal fascia and muscles while respecting the peritoneum. For each rabbit, the defect was repaired by four different large pore size prostheses which varied according to the material used: two with monofilament of heavy (75 g/m 2) or low (38 g/m 2) weight polypropylene (PP), and two with multifilament of heavy (115 g/m 2) or low (59 g/m 2) weight polyethylene-terephthalate (PET). Animals were sacrificed in groups of 10 after 14, 30, 90 and 180 days to evaluate contraction, solidity and elasticity of the prostheses. Results PP and PET retracted, independently of their weight, in 81.25% and 20% respectively. Intensity of contraction was not predictable but median value of retracted surface was 14% with PP, none with PET. Contraction settled quickly after tissue integration and did not subsequently occur. Heavyweight PET was considered the most solid material (70 N cm −1), low-weight PP the most fragile (20 N cm −1). Heavy forms of PP or PET resisted better to the rupture than the light forms which were sometimes insufficient to resist the extreme values of the human abdominal pressure (16 N cm −1). PP was more flexible than PET, but PET was the only form which was able to support extreme values of the abdominal pressure and remain in the elastic range. Duration of implantation did not modify solidity or elasticity of the prostheses. Conclusion In our abdominal rabbit model, as regards mechanical properties, heavyweight PET seems to be the optimal biomaterial.

Influence of Bitumen Colloidal Nature on the Design of Isocyanate-Based Bituminous Products with Enhanced Rheological Properties

This work deals with the influence that bitumen colloidal nature exerts on the rheological properties of bitumen samples modified by isocyanate-based reactive polymers. Shear rheology tests, modulated differential scanning calorimetry (MDSC), chemical characterization by TLC-FID, and AFM microstructural analysis were carried out on four different 150/200 penetration neat bitumen samples and the corresponding MDI-PPG (a low molecular weight polypropylene glycol functionalized with a polymeric 4,4′-diphenylmethane diisocyanate) modified binders. The results obtained demonstrate that the bitumen modification degree depends on bitumen reactivity and microstructure. Thus, the highest modification capability is obtained with neat bitumen samples that exhibit both a well-developed three-dimensional network and a high chemical reactivity with the isocyanate groups. The results obtained may be used to improve the performance of these materials, according to their final application.

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.

SUBSTITUENT EFFECTS OF tert-BUTYL GROUPS ON FLUORENYL LIGAND OF [t-BuNSiMe2FLu] ZrMe2

[t-BuNSiMe2(2,7-t-Bu2Flu)]ZrMe2 and [t-BuNSiMe2(3,6-t-Bu2Flu)]ZrMe2 were synthesized, and the solid structure of complex [t-BuNSiMe2(2,7-t-2Flu)]ZrMe2 was elucidated by single crystal X-ray analysis. These complexes were applied for propylene polymerization using dried modified methylaluminoxane as a cocatalyst at 0°C and 20°C in toluene. Both systems did not show activity at 0°C, but they conducted the polymerization at 20°C. The introduction of t-butyl substituents to the fluorenyl ligand improved the activity more than six times regardless of the position of the substituents, and both systems gave low molecular weight polypropylenes (PP) with narrow molecular weight distribution. The introduction of t-butyl substituents also improved the syndiospecificity and [t-BuNSiMe2(3,6-t-Bu2Flu)]ZrMe2 gave highly syndiotactic PP with the syndiotactic pentad of 0.91 and the melting point of 145°C.

The Preparation and Study on Ultrahigh Molecular Weight Polypropylene Gel‐spun Fibers

A novel polypropylene (PP) fiber was prepared by using gel spinning/crystallization from dilute solutions of ultrahigh molecular weight isotactic polypropylene (i‐UHMWPP), and subsequently drawing at various temperatures. The influence of drawing temperature on the properties of the resulted fibers was investigated. We found that the draw‐ability and mechanical as well as crystallization properties of the fibers obtained were dramatically improved with increasing drawing temperature. When the drawing temperature is below the α‐crystal relaxation temperature of PP, which was measured by wide‐angle X‐ray diffraction (WAXD) analysis as 100–120°C, the fibers are characterized by lower crystallinity and smaller crystals with less perfection, resulting in brittle fracture and subsequently poor mechanical durability. With drawing at temperatures above the α‐crystal relaxation temperature of PP, a novel UHMWPP fiber with Young's modulus of 27 GPa and tensile strength of 1.3 GPa was obtained. Higher crystallinity and larger crystals with better perfection and orientation were observed in this fiber.

Rheological, mechanical and thermal properties of propylene‐ethylene block copolymer/polyalphaolefins blends

AbstractThe rheological, thermal, and mechanical properties of propylene–ethylene block copolymer (PPB) blends with predominantly atactic molecular structure of low molecular weight polypropylene and propylene copolymers with either ethylene or 1‐butene (APAO) have been studied. It has been found that blend properties depend on comonomer type, content, and molecular weight of APAO as well as blend composition. APAO having ethylene comonomer showed better miscibility with PPB than the other ones, and high comonomer content of APAOs gave dramatic increase in impact strength over 30 wt%. It has been concluded that APAO can be used as an effective modifier of PPB. POLYM. ENG. SCI., 47:1905–1911, 2007. © 2007 Society of Plastics Engineers

Comparative Evaluation of Adhesion Formation, Strength of Ingrowth, and Textile Properties of Prosthetic Meshes After Long-Term Intra-Abdominal Implantation in a Rabbit

Effective laparoscopic ventral herniorrhaphy usually mandates the use of an intraperitoneal prosthetic. Visceral adhesions and changes in textile characteristics of prosthetics may complicate repairs, especially long-term. The aim of this study was to compare the adhesion formation, tissue ingrowth, and textile characteristics one year after intra-abdominal placement of the commonly used prosthetic meshes. Forty (4 x 4 cm) meshes were sutured using absorbable suture to an intact peritoneum in 20 New Zealand white rabbits. The study groups included: polypropylene (PP) [Marlex; C.R. Bard Inc, Cranston, NJ], expanded polytetrafluoroethylene (ePTFE) [DualMesh; WL Gore, Flagstaff, AZ], ePTFE and PP (ePTFE/PP) [Composix, C.R. Bard Inc], reduced weight PP and oxidized regenerated cellulose (rPP/C) [Proceed; Ethicon, Inc, Somerville, NJ]. The meshes were explanted after one year. Adhesions were scored as a percentage of explanted biomaterials' affected surface area. Prosthetic shrinkage was calculated. The strength of incorporation and mesh compliance were evaluated using differential variable reluctance transducers. Mesh ingrowth was measured as the load necessary to distract the mesh/tissue complex. Mesh compliance was calculated as the change in linear displacement of the sensors due to applied load. The groups were compared using Student's t-test and Fisher's exact test. ePTFE had significantly less adhesions (0%) than both ePTFE/PP (40%) and PP (80%) groups (P < 0.001). The mean area of adhesions for the rPP/C (10%) and the ePTFE/PP (14%) groups was less than that for the PP group (40%) (P = 0.02). Prosthetic shrinkage was greatest in the ePTFE (32%) group than in any other group (P = 0.001). There were no differences in mesh incorporation between the groups. At explantation, mesh compliance in the ePTFE group was superior to other meshes (P < 0.0001). The rPP/C mesh induced the smallest change in the compliance of the tissue adjacent to the mesh (P = 0.0001). Prosthetic materials demonstrate a wide variety of characteristics. Although exposed PP formed the most adhesions, up to 40% of the other PP-based meshes formed adhesions despite protective barriers. The ePTFE mesh did not induce adhesions and was the most compliant, however, this prosthetic's contraction was greatest. Reduced weight polypropylene (rPP/C) mesh induced the smallest change in the adjacent tissue pliability/compliance. Understanding of the long-term effects of various prosthetic materials is important to ensure an adequate hernia repair while minimizing postoperative morbidity and patient discomfort.

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.