Structure-property relations in polypropylene mica composites

Polypropylene composite samples with concentrations of mica of 10, 20, 30, 40, 45, 50, and 60 wt percent were prepared under identical conditions by injection molding. The influence of mica concentration on the structure and mechanical properties of the composites was investigated using a polarizing microscope, scanning electron microscope, differential scanning calorimetry, and stress-strain characteristics. Flexural and impact strengths show an initial rise and then gradual fall with increasing mica concentration. An optimum of these properties occurred at ∼20 wt percent mica. Tensile modulus and heat distortion temperature show a continuous rise; whereas the percent elongation decreased with mica content. These changes in properties are discussed in terms of a skin-core morphology, transcrystallinity, crystallinity, fracture surface morphology, flake orientation, and interfacial adhesion in these composites. This study helps in optimizing the mica concentration for injection molded composites.     

Structure-property relationships on uniaxially oriented carbon nanotube/polyethylene composites

Multi walled carbon nanotubes have been incorporated into a linear low density polyethylene matrix through high energy ball milling technique at room temperature, without any chemical modification or physical treatment of the nanotubes. Highly oriented samples, with different draw ratios, were obtained by drawing at 80 °C the composite films. SEM and FTIR results on the drawn PE films demonstrate that the molecular chains in both crystalline and amorphous phases are well oriented along the drawing direction. The effect of different weight percent loadings of nanotubes and draw ratio on the morphology, thermal, mechanical and electrical properties of the composite fibers have been investigated.     

Structure-property relationships in nanocomposites

A numerical finite-difference model is presented for the study of the factors controlling the properties of composites reinforced with platelets and fiber-like nano-inclusions. The approach provides a comprehensive treatment of the dependence of composite modulus and strength on the shape of the inclusions and the interrelated effects of their orientation, volume fraction, aspect ratio, modulus and interfacial properties with the matrix. At the same volume fraction, we find that platelets are generally more efficient than fibers in improving composite modulus. This is rationalized through our model finding that fibers have a typically low critical aspect ratio value, which puts an upper limit to their reinforcement potential. Platelets also turn out to be superior to fibers in all nanocomposites characterized by a poor orientation of the inclusions. We also find that low interfacial adhesion and poor dispersion of the inclusions lead to a decrease in reinforcement efficiency. Turning to comparison with experiment, a good agreement is found between our model predictions and modulus data on nanocomposites reinforced with montmorillonite platelets and carbon nanotubes.     

Structure-property relationships in thermoplastic elastomers: I. Segmented polyether-polyurethanes

Segmented poly(ether-b-urethanes) have been synthesized with 2000 MW polypropylene oxide coupled with diisocyanates and diol type chain extenders. The diisocyanates used were symmetric rigid 4, 4′-diphenylmethane diisocyanate (MDI), linear aliphatic hexamethylene diisocyanate (HDI), and unsymmetric rigid toluene-2, 4-diisocyanate (TDI). The chain extenders were symmetric N, N′-bis(2-hydroxyethyl) terephthalamide (BT) and N, N′-bis(2-hydroxyethyl)-hydroquinone (BH) unsymmetric N, N′-bis(2-hydroxyethyl)isophthalamide, and linear aliphatic 1, 4-butanediol (B). Hard segment contents ranged from 20 to 40 wt percent. The thermal behavior of these materials is consistent with phase separation into separate hard and soft domains, In order of increasing temperature above the soft segment T_g, there are transitions which occur in the regions ?56 to ?36°C (T_a), 70 to 90°C (T_b), and 138 to 168°C (T_m). The former is probably associated with soft segment change from a viscoelastic to an elastomeric state. Values of T_a are ～ ?51 C and ?56°C for the MDI-BT and HDI-BT polymers, respectively, and are independent of hard segment content. Microscopy showed that the former polymers have spherulitic morphology, so these materials have good microphase separation and exhibit crosslinked elastomeric properties. The TDI-BT or BI and MDI-B polyurethane have composition-independent T_a values of ?41 and ?36°C, respectively. These materials probably have considerable “domain-bound-ary-mixing”. At low hard segment content the MDI-B polymers behave as non-crosslinked elastomers. Only the MDI-BI polymers have _Ta values, which are strongly affected by composition, increasing in magnitude with increasing of hard segment content. This is interpreted as significant “mixing-in-domains” and is supported by morphology observed by microscopy. The next higher transition, T_b, probably involves dissociation of interdomain hydrogen bonding. In the case of the MDI-BT polyurethanes, the spherulites associated with the hard domains had disappeared at 141°C and the few small spherulites in the MDI-BI polymers disappeared at 130°C. The T_b values are 70, 83 to 90, and 100°C for the MDI-B, HDI-BT, and HDI-BI polymers, respectively. The melting transitions occurred between 138 to 168°C for the various polyurethanes except for the MDI-BT systems which decompose before melting. Thermal decomposition is a two-stage process. Hard segments decompose between 200 and 300°C. The initial decomposition temperatures are lowered in the presence of strong acid. Soft segments decompose at higher temperatures. The mechanical properties of the MDI-BI polyurethanes are charateristic of crosslinked elastomer, the results of which will be presented in a subsequent paper.     

Silphenylene and silphenylene-siloxane oligomers: Structure-property relationships

Some representative oligomers were prepared by polycondensation reactions of dimethyldichlorosilane with 1,4-di-Grignard reagent prepared from 1,4-dibromobenzene in diethyl ether. The structural characterization of the oligomers was carried out by FTIR and¹H,¹³C, and²⁹Si NMR spectroscopy. TheM _n values were determined by vapor pressure osmometry. TheT _g values were measured by DSC and the thermodegradation process was analyzed by TGA. In all cases the oligomers prepared in the absence of the blocking end group showed siloxane units in the main chain, which were quantified by¹H and²⁹Si NMR.²⁹Si NMR was also used to determine the oligomer sequence. It was possible to correlate the and structure withT _g and with temperature at 3% weight loss. The results agree with these obtained for structurally similar polymers.     

Structure-property relationships in amorphous polyamides

New methods are put forward to explain the numerical values of some useful bulk physical properties of amorphous copolyamides, in terms of parameters related to monomer structure. Polyamides based on adipic, tetramethylsuberic, iso- and tere-phthalic acids, and diamines including isophorone, xylylene, cyclohexane, hexamethylene and its trimethyl derivatives, methylnonane and dodecamethylene diamines were studied. ε-Caprolactam and 12-aminododecanoic acid were also used as comonomers. In Part I, an empirical rule is proposed, based on experimental observations which predicts whether a copolyamide has an amorphous or crystalline character. The rule is based on the individual stereochemical contributions of the constituent monomers to the overall polymer chain structure. A relationship between Vicat softening point and monomer composition is derived from experimental data, which seems to be generally applicable to all amorphous polyamides of the diacid/diamine type. Each monomer makes a molar contribution which has been determined experimentally for all the materials studied. An arbitrary set of simple structural rules has been devised which enables the molar contributions of monomers to be related to their chemical structure. This procedure provided a method of predicting the contributions of other monomers for which molar constants had not been measured, and was successfully tested for a limited number of materials. A modified relationship was obtained experimentally to explain the effect of amino-acids on Vicat softening point.In Part II, the relationships outlined in Part I are combined on the basis of experimental evidence to provide an empirical relationship between composition and impact strength. This relationship predicted the impact strengths of the majority of eighty copolyamides, of widely different chemical structure, with a reasonably good accuracy. Substantial inaccuracy occurred only when a large proportion of a long chain aliphatic monomer was present in the polyamide. Tentative correlations between tensile strength and carbon chain length were observed from a limited number of measurements which suggests that tensile strength may be a constitutive property. The main conclusions of this work are: (a) polyamides are naturally crystalline with high melting points if more than 80% of the monomer units are symmetrical; (b) Vicat softening point and tensile strength decrease linearly with increasing monomer chain length; the softening point is particularly affected by the presence of substituent groups; (c) amino-acids reduce symmetry, impact strength and Vicat softening points of copolyamides; (d) Charpy impact strength increases with the proportion of symmetric monomer units, the rigidity of the acid and flexibility of the diamine structures; (e) tensile strength and flexural modulus correlate with each other in copolyamides of diacids and diamines and both increase as the amount and chain length of aliphatic monomer is reduced; (f) by using the empirical relationships developed in this work, it has proved possible to formulate amorphous polyamides with outstanding combinations of physical properties, when compared with commercially available polymers.     

Structure-property relationships in rubber-toughened epoxies

Epoxies toughened with two reactive liquid rubbers, an epoxy-terminated butadiene acrylonitrile rubber (ETBN) and an amino-terminated butadiene acrylonitrile rubber (ATBN), were prepared and studied in terms of their structure property relationships. A two-phase structure was formed, consisting of spherical rubber particles dispersed in an epoxy matrix. A broad distribution of rubber particles was observed in all the materials with most of the particles ranging in size from 1 to 4 μm, but some particles exceeding 20 μm were also found. Impact strength, plane strain fracture toughness (K_IC), and fracture energy (G_IC) were increased, while Young's modulus and yield strength decreased slightly with increasing rubber content and volume fraction of the dispersed phase. Both G_IC and K_IC were found to increase with increasing apparent molecular weight between crosslinks and decreasing yield strength. The increased size of the plastic zone at the crack tip associated with decreasing yield strength could be the cause of the increased toughness. An ATBN-toughened system containing the greatest amount of epoxy sub-inclusion in the rubbery phase demonstrated the best fracture toughness in this series. In the present systems, rubber-enhanced shear deformation of the matrix is considered to be the major toughening mechanism. Curing conditions and the miscibility between the liquid rubber and the epoxy resin determine the phase morphology of the resulting two-phase systems. Kerner's equation successfully describes the modulus dependence on volume fraction for the two-phase epoxy materials.     

Structure-property relationships in dendritic encapsulation

Several molecular structure-property relationships are presented and compared to illustrate our current understanding of macromolecular encapsulation using dendrimers. Specifically, the effect that dendrimer architectures have on encapsulating photoactive and redox-active units fixed at the molecular core is considered.     

Lignin–polypropylene composites. II. Plasma modification of kraft lignin and particulate polypropylene

Indulin kraft lignin and polypropylene were subjected to plasma treatments in a rotating electrodeless plasma reactor at 13.56 MHz radio frequency, with the goal of improving the strength properties of the composites made from these materials. It was shown that efficient surface modification could be achieved by these plasma treatments, avoiding long reaction times and large volumes of reactants for modification by conventional wet chemistry. SiCl₄‐plasma treatments of lignin at 100 and 200 W resulted in silicon implantation in the range of 4–10% that depended on the treatment time. However, the effect of power in the treatments was minimal, given that changes in silicon implantation were not observed for changes in this parameter. SiCl₄‐plasma treatment of polypropylene at 80 W, 1 and 10 min, resulted in silicon implantation in the order of 10–15%, for the two different treatment times, showing that low power and short treatment times were sufficient to significantly alter the polypropylene surface. However at high power (250 W), the longer treatment time of polypropylene apparently led to formation of oligohalosilanes. Other plasma treatments in the rotating reactor such as plasma‐induced copolymerization of acryloyl chloride on both lignin and polypropylene, and plasma‐state polymerization of acryloyl chloride on polypropylene under pulsing conditions, resulted in thin film depositions. Evaluation of composites from these treated materials is described in the next contribution (Part III) from this series. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1920–1926, 2004     

Structure-property relationships in thermoplastic elastomers III. Segmented polyacetal-polyurethanes

Dihydroxy-terminated polyacetals had been synthesized from aldehydes and glycols and used as soft segments to obtain segmented polyurethane block copolymers. For soft segment ≥ 1700 M _n, the T_g ranges from–48 to ?58°C and is insensitive to the structures of diisocyanate and chain extender. The T_g of PacPU with 1350 M _n polyacetals is raised to ?38°C, and none was observed for shorter polyacetal chains. The copolymers can be synthesized to have a broad range of mechanical properties, such as modulus from 0.5 to 130 MPa, stress at break from 0.7 to 21 MPa, and elongation at break from 66 to 1300% through the variation of the constituents and composition. The rheologic properties are only slightly dependent on temperature for symmetrical diisocyanates but quite temperature sensitive with asymmetric diisocyanate copolymers. The polyacetals are selected to build in acid-catalyzed thermal decomposition of the thermoplastic elastomers. The extreme acid sensitivity of the polyacetal block is buffered in the coplymers.     

Mechanical properties and morphology of polypropylene composites II. Effect of polar components in talc-filled polypropylene

Using the concept of filler coating, a study has been made of the morphology and mechanical properties of polypropylene/talc/elastomer composites with a series of polar components as added elastomers. Both impact strength and stiffness of the blends were better than those of polypropylene homopolymer. Most of the polar components showed a considerable amount of filler coating, as evidenced by morphological studies. However, the impact strength of the composites was generally lower than that of similar blends with non-polar elastomers, probably owing to (a) the high glass transition temperatures of the polar components, (b) the poor dispersion of some of the elastomeric phases, and (c) a reduced affinity of the elastomers for polypropylene.     

Structure-property relationships in elastomer-modified terpolymer systems

A number of terpolymers, incorporating as the elastomer phase polybutadiene, polyisoprene, poly-2,3-dimethylbutadiene, poly(butadiene-co-styrene), and poly(butadiene-co-2-methyl-5-vinypyridine), were studied. Matrices were composed of poly(styrene-co-acrylonitrile) (SAN), poly(α-methylstyrene-co-acrylonitrile), and poly(styrene-co-acenaphthylene). At constant elastomer content and elastomer molecular weight in systems employing a SAN matrix, Izod impact resistance was found to vary inversely with rising elastomer-glass transition temperature. In systems of various matrix composition, using a polybutadiene elastomer, heat deflection temperatures were found to very directly and impact resistance inversely with rising matrix-glass transition temperature. In acrylonitrile–butadiene–styrene (ABS), systems of constant matrix composition and elastomer content, varying the elastomer molecular weight from 0.6 to 2.6 × 10⁵ resulted in increasing the Izod impact resistance from 0.67 to 12.8 ft-lb/in. of notch.     

Structure-property relations in molded, nucleated isotactic polypropylene

The influence of molecular characteristics and nucleating agents on the morphology distribution and properties of injection molded isotactic polypropylene (iPP) is investigated using optical microscopy, X-ray diffraction and mechanical testing. To have better control over the thermo-mechanical history, instead of a reciprocating screw, a capillary rheometer is used to drive the melt into the simple rectangular mold. Molecular weight (MW), molecular weight distribution (MWD) and addition of ethylene via copolymerization all influence the thickness of the oriented shear layer, the crystallinity, the type and amount of crystal phases, and the lamellar thickness. The addition of a nucleating agent (DMDBS), dictates the crystallization process, and resulting morphology, and samples with an oriented morphology over the full thickness are created without changing other morphological features, by applying a thermal treatment to the melt prior to injection, which is based on the specific phase behavior of the iPP-DMDBS system. The thermally treated samples show a considerable improvement in mechanical properties.     

Transcrystallinity phenomena in fiber-reinforced polypropylene. II: Morphology,thermal and mechanical properties relationships

The effect of short-length carbon and Kevlar fibers on the crystallization of isotactic polypropylene (iPP) in composites prepared by compression molding has been investigated. The tendency of carbon and Kevlar fibers to nucleate the iPP during isothermal and nonisothermal crystallization has been evaluated by differential scanning calorimetry. The influence of different thermal histories used to prepare the unreinforced and reinforced samples on the crystallization parameters of iPP was examined. In addition, the tensile behavior was related to the resulting morphologies of the samples. It was observed that the crystallinity content, obtained by using different thermal treatments (slowly cooling or quenching), gives rise to different morphologies by influencing the mechanical behavior of materials as well. Moreover, the composites obtained by slow cooling seem to present a better fibber/matrix adhesion then that found in quenched samples. Possible underlying microstructures, which can explain the properties and the morphological characteristics, are also discussed.     

Structure-property relationships in cross-linked polyester-clay nanocomposites

Crosslinked polyester-clay nanocomposites were prepared by dispersing organically modified montmorillonite in prepromoted polyester resin and subsequently crosslinked using methyl ethyl ketone peroxide catalyst at several different clay concentrations (1.0, 2.5, 5.0, and 10.0 wt%). X-ray diffraction studies revealed the formation of a nanocomposite in all cases with the disappearance of the peak corresponding to the basal spacing of the pure clay. Transmission electron microscopy was used to study the morphology at different length scales and showed the nanocomposite to be comprised of a random dispersion of intercalated/exfoliated aggregates throughout the matrix. Thermal degradation of the nanocomposites was found to be slightly but progressively hastened compared to the pure crosslinked polymer, loss and storage modulus were monotonically shifted toward higher frequency values, and the tensile modulus was found to decrease with increasing clay content. These unexpected results were rationalized based on the decrease in the degree of crosslinking of the polyester resin in the nanocomposite, in the presence of clay. In particular, the nanocomposite containing 2.5 wt% clay consistently demonstrated a drop in properties far greater than that observed at other clay concentrations, and was attributed to the greater degree of exfoliation seen in this case which presumably leads to a greater decrease in the degree of crosslinking. Oxygen permeability rates in the polyester nanocomposites decreased with increasing clay content, as expected, and was satisfactorily reproduced using a tortuosity based model.     

Structure-property relationships in novel polydiacetylene-containing oligoester: Polyolefin blends

Summary The paper describes thermal and mechanical properties of a series of novel blends prepared using a two-stage process which invloved solution blending a specially-synthesised diacteylene-containing oligoester (DOE) with a semi-crystalline poly[ethylene-co-(vinyl acetate)] (EVA), followed by conversion of the DOE to a polydiacteylene-containing oligoester (cp-DOE) by in situ thermal cross-polymerisation during moulding. Moulded blends range from ductile to brittle materials and give intense Raman spectra in which the CC stretching band at 2100 cm^-1 is well-defined and shifts to lower wavenumber when the blends are subjected to tensile stress. For each blend composition, shifts in wavenumber were used to determine local stress in the cp-DOE component independently of the overall stress applied to blend.     

Structure-property relationships in PMR-type polyimide resins: 1. Novel anthraquinone-based PMR resins

Novel aromatic polyimides prepared via the polymerization of monomeric reactants (PMR) approach and incorporating anthraquinone diamines in the main chain have been characterized. Imidization and crosslinking reaction profiles have been delineated by d.m.t.a. and the high-temperature mechanical and thermal properties of the thermoset resins examined. Elevated glass transition temperatures (> 300°C) are apparent in some resins while impairment of mechanical integrity is not evident below 450°C. All resins show good thermal and thermo-oxidative stability.     

Polyurethane elastomers containing polybutadiene and aliphatic diols: Structure-property relationships

The effect of aliphatic diols on the structure and some mechanical properties of polyurethane elastomers containing hydroxyl-terminated polybutadiene and three different diisocyanates was studied. Differential scanning calorimetric studies revealed the existence of several thermal transitions, characteristic of structures of multiphased elastomers. Three transition temperatures, a subzero transition and two high temperature transitions, were found in some of the elastomers. The higher-high temperature transition reflects ordered domains, also supported by X-ray diffraction, Higher degree of order was achieved with longer diols. The mechanical behavior is affected by the multiphase nature of the elastomers, especially by the morphology of the hard segment domains. The structureproperty relationships for the three component polyurethane elastomers in question thus have been established.     

Phenolic rigid organic filler/isotactic polypropylene composites. II. Tensile properties

A novel phenolic rigid organic filler (KT) was used to modify isotactic polypropylene (iPP). The influence of KT particles on the tensile properties of PP/KT microcomposites was studied by uniaxial tensile test and the morphological structures of the stretched specimens were observed by scanning electron microscopy (SEM) and polarized optical microscopy (POM). We found that the Young’s modulus of PP/KT specimens increased with filler content, while the yield and break of the specimens are related to the filler particles size. The yield stress, the breaking stress and the ultimate elongation of PP/KT specimens were close to those of unfilled iPP specimens when the maximal filler particles size is less than a critical value, which is 7 μm at a crosshead speed of 10 mm/min and 3 μm at 200 mm/min, close to that of glass bead but far more than those of other rigid inorganic filler particles. The interfacial interaction was further estimated from yield stress, indicating that KT particles have a moderate interfacial interaction with iPP matrix. Thus, the incorporation of small KT particles can reinforce iPP matrix and simultaneously cause few detrimental effects on the other excellent tensile properties of iPP matrix, due to their organic nature, higher specific area, solid true-spherical shape and the homogenous dispersion of the ROF particles in microcomposites.     

Phenolic rigid organic filler/isotactic polypropylene composites. II. Tensile properties

A novel phenolic rigid organic filler (KT) was used to modify isotactic polypropylene (iPP). The influence of KT particles on the tensile properties of PP/KT microcomposites was studied by uniaxial tensile test and the morphological structures of the stretched specimens were observed by scanning electron microscopy (SEM) and polarized optical microscopy (POM). We found that the Young’s modulus of PP/KT specimens increased with filler content, while the yield and break of the specimens are related to the filler particles size. The yield stress, the breaking stress and the ultimate elongation of PP/KT specimens were close to those of unfilled iPP specimens when the maximal filler particles size is less than a critical value, which is 7 ?m at a crosshead speed of 10 mm/min and 3 ?m at 200 mm/min, close to that of glass bead but far more than those of other rigid inorganic filler particles. The interfacial interaction was further estimated from yield stress, indicating that KT particles have a moderate interfacial interaction with iPP matrix. Thus, the incorporation of small KT particles can reinforce iPP matrix and simultaneously cause few detrimental effects on the other excellent tensile properties of iPP matrix, due to their organic nature, higher specific area, solid true-spherical shape and the homogenous dispersion of the ROF particles in microcomposites.