Studies on the thermal and mechanical behavior of PLA‐PET blends

The increasing use of bio‐sourced and biodegradable polymers such as poly(lactic acid) (PLA) in bottle packaging presents an increasing challenge to the polyethylene terephthalate (PET) recycling process. Despite advanced separation technologies to remove PLA from PET recyclate, PLA may still be found in rPET process streams. This study explores the effects of PLA on the mechanical properties and crystallization behavior of blends of PET containing 0.5–20% PLA produced by injection molding. SEM indicates an immiscible blend of the two polymers and TGA confirms the independent behavior of the two polymers under thermal degradation conditions. Temperature‐modulated DSC studies indicate that adding PLA to PET increases the rigid amorphous fraction of the PET moiety. Critical amounts of PLA induce stress oscillation behavior during mechanical testing. The mechanical behavior of the samples is explained by antagonistic interaction between increased rigid amorphous fraction and decreased fracture strength arising from an increased population of PLA microparticles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44147.     

Mechanical properties of acrylate networks formed by visible laser-induced polymerization. I. Dependence on photopolymerization parameters

The mechanical properties of network molecular systems, prepared through visible (Ar⁺) laser-induced polymerization of multifunctional acrylates, were studied as a function of some of the photopolymerization parameters. The properties investigated were the Young's modulus of elasticity and the stress-at-break, both derived from the stress versus strain test of dogbone-shaped photopolymerized samples. The parameters studied included the dye and co-initiator concentrations, and the laser power. We also compared the mechanical properties of samples made using different types of fluorone dyes and using two different amines as co-initiator. Better polymers are formed by the dyes with low fluorescence quantum yield. The three photopolymerization parameters modify the mechanical properties in a very similar way: they initially tend to increase both the Young's modulus and the stress-at-break but have a deleterious effect on the material strength if used in excess. N-phenylglycine, NPG, was shown to form stronger polymers (higher Young's modulus) than if N,N-dimethyl-2,6-diisopropylaniline, DIDMA, was used as co-initiator. We discuss the possible molecular mechanisms for such observations. © 1994 John Wiley & Sons, Inc.     

Production of non‐crosslinked thermoplastic foams with a controlled density and a wide range of cellular structures

A novel foaming route, with respect to existing industrial foaming processes, called “Improved Compression Molding” (ICM), which allows producing non‐crosslinked thermoplastic foams in a wide density range, is described in this work. This process is different from others because it is possible to control independently density and cellular structure and therefore, tailored cellular polymers can be produced. To understand the process, a collection of polypropylene foams, with relative densities ranging from 0.3 to 0.6 were produced. The influence of foaming parameters, on foams microstructure and mechanical response was analyzed. Results revealed that for similar densities, foams with different open cell content and cell size can be achieved. In addition, it was proved that mechanical behavior strongly depends on the degree of interconnectivity of the cells. The analysis of the relative mechanical properties allowed determining the influence of microstructure on mechanical behavior as well as quantifying the efficiency of the foaming process to produce light‐weight stiff materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42324.     

Crosslinking of bimodal polyethylene

Two bimodal polyethylenes, differing only in polymerisation order, were investigated with respect to crosslinking behaviour and network properties. The crosslinked materials were examined using size exclusion chromatography (SEC), gel-content measurements, and calculations of the network density. Dynamic mechanical analyses in the melt were performed to monitor the crosslinking and to provide another measure of the network density. The experiments were performed to investigate any potential influence of the polymerisation order on the crosslinking as well as to study the network formation in the crosslinked polymers. The bimodal polyethylenes were also compared to two monomodal polyethylenes representing the short chain branched, high molecular weight fraction, and the linear, low molecular weight fraction, respectively. The SEC measurements clearly showed how the crosslinking starts with the consumption of the high molecular weight fraction. The gel-content measurement showed the importance of a high molecular weight material for the gel formation. The network density calculations demonstrated how long chains can give rise to apparent networks which are mainly due to chain entanglements. The experiments showed that the polymerisation order for the bimodal polyethylenes has no effect on the crosslinking.     

Blends of triazine‐based hyperbranched polyether with LDPE and plasticized PVC

Triazine‐based hyperbranched polyether was obtained by earlier reported method and blended with low density polyethylene (LDPE) and plasticized poly(vinyl chloride) (PVC) separately to improve some desirable properties of those linear polymers. The properties like processability, mechanical properties, flammability, etc. of those linear polymers were studied by blending with 1–7.5 phr of hyperbranched polyether. The mechanical properties were also measured after thermal aging and leaching in different chemical media. SEM study indicates that both polymers exhibit homogenous morphology at all dose levels. The mechanical properties like tensile strength, elongation at break, hardness, etc. of LDPE and PVC increase with the increase of dose level of hyperbranched polyether. The flame retardant behavior as measured by limiting oxygen index (LOI) for all blends indicates an enhanced LOI value compared to the polymer without hyperbranched polyether. The processing behavior of both types of blends as measured by solution viscosity and melt flow rate value indicates that hyperbranched polyether acts as a process aid for those base polymers. The effect of leaching and heat aging of these linear polymers on the mechanical properties showed that hyperbranched polyether is a superior antidegradant compared to the commercially used N‐isopropyl‐N‐phenyl p‐phenylene diamine. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 648–654, 2007     

Synthesis and characterization of polymers from soybean oil and p‐dinitrosobenzene

In this study, rubbery, bio‐based thermoset polymers were synthesized from soybean oil (SO) and p‐dinitrosobenzene (DNB) via an ene reaction. Polymeric p‐dinitrosobenzene (PDNB) was synthesized from p‐quinone dioxime and was thermally depolymerized in the presence of SO. SO/PDNB polymers were synthesized by a two‐stage polymerization. During the reaction, the role of different parameters such as mol ratio of SO and PDNB, preheating temperature of SO, polymerization time, and temperature were examined. Polymerization was followed by IR spectroscopy, and the polymers obtained were characterized by dynamic mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry. The polymers have glass transition temperature ranging from ?51.5°C to ?46.3°C, whereas their storage moduli are between 430 and 210 MPa at ?60°C. Thermogravimetric analysis reveals that all of the polymers have temperatures of maximum degradation around 500°C. The crosslinked network structure of the polymers was investigated by swelling behavior and surface hardness test. Methyl oleate was used as a model compound to examine the chemical structure of the products. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Prodegradant effect of titanium dioxide nanoparticulates on polypropylene–polyhydroxybutyrate blends

Polymers are gradually replacing conventional materials in various sectors of the economy because of their low cost and broad functionality. However, the high stability of polymers under most environmental conditions can lead to their accumulation in the form of waste. Polyhydroxybutyrate (PHB) is an alternative because of its biodegradability, but it is usually expensive and brittle. These aspects can be improved through the formation of blends, such as with polypropylene (PP). The objective of this study was to investigate the possibility of using titanium dioxide (TiO₂) nanoparticles as a prodegradant agent in the PP–PHB–TiO₂ system through the evaluation of the effects of these nanoparticles under UV light on the structure and properties of the materials. Samples were produced through extrusion and injection molding and were characterized by their mechanical and thermal properties and structural analyses. The results show that the TiO₂ nanoparticles were able to act as a prodegradant agent for the PP–PHB blend; they also successfully improved some of the mechanical and dynamic mechanical properties of the blend. However, a TiO₂ nanoparticle content higher than 7.5 wt % was not able to extend the photodegradation process further, possibly as a consequence of the agglomeration of nanoparticles during the processing of these more concentrated blends. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46636.     

The water curing of a polyurethane resin used as a wool fiber coating

In the industrial application of polyurethane resins to form surface coatings on wool fabrics, the prepolymer resin Synthappret is curred by reaction with water, either as steam or as atmoshpheric water vapor, to form the rubber network. This paper examines changes in the mechanical properties of the resin with cure conditions. It is shown for steam-cured resin that the initial modulus, the equilibrium swelling in tetrachloroethylene, the Mooney-Rivlin constant C₁, and the average molecular weight of chain segments between crosslinks all reach constant values after 1 hr. However, the resin density and the Mooney-Rivlin constant C₂ show a linear dependence on cure time with no indication of reaching an equilibrium value. It is concluded that although the network is substantially complete after 1 hr of steam cure, there is a continuing pattern of reorganization. The mechanical properties of resin produced by air curing, a much slower process, are consistent with those of a network which has had a longer period of reorganization. The density of air-cured resin is significantly higher than that of resin prepared by steam curing. Stereoscan electron micrographs of the resin surface reveal a texture which coarsens with prolongation of cure time and also reveal a difference for the two methods of cure.     

Compatibilization of blends of polyethylene with a semirigid liquid crystalline polymer by PE-g-LCP copolymers

The blends of thermoplastics with liquid crystalline polymers show, in general, poor properties because of the lack of adherence between the two phases. The use of ad hoc synthesized copolymers containing the monomer units of the two polymers has been recently considered by some of us for blend compatibilization, and the results appear promising. In this work, new PE-g-LCP copolymers, prepared either by the synthesis of the LCP in the presence of a functionalized PE, or by reactive blending of the latter polymer with preformed LCP, have been employed as compatibilizing additives for blends of PE with a semirigid LCP. The morphology and the rheological and mechanical properties of the ternary blends, compared with those of samples without compatibilizers, or containing conventional maleic anhydride grafted PE, indicate that the PE-g-LCP copolymers do in fact lead to an improvement of interfacial adhesion, both in the melt and in the solid state, as well as to a modest enhancement of the mechanical properties. The results may be rationalized considering that the PE-g-LCP copolymers used by us consist of fairly short PE backbones with LCP grafts of various length. The molecules with longer LCP branches are thought to become mixed at the surface of the LCP particles and to give rise to fairly weak interaction with the PE matrix. It is argued that new PE-g-LCP copolymers synthesized from higher molar mass functionalized PE samples might show much better compatibilizing performance.     

A study of the effect of pressure,time, and temperature on high-pressure powder molding

High pressure room temperature molding of polymeric powders has been found to be a useful technique for producing parts from certain hard-to-process polymers and certain common polymers. Polymeric powders of less than 175μ were compacted at pressures up to 0.689 GPa. Subsequent heat treating of the compacted samples improves the mechanical properties of the samples to levels comparable to those attained by other techniques. Thermosetting or reactive polymers which do not evolve vapors during curing are readily processed by this technique. Semicrystalline polymers which are molded above their T_g are also easily processed by this method. Glassy polymers, in general, have not been found to be processable. The important process variables are molding pressure, molding time and heat treating temperature and time. The process relies on particle-to-particle fusion by either chemical reaction or localized melt fusion. For semicrystalline polymers, the annealing temperature is within the melting endotherm. Reactive polymers cure at their optimum curing temperature.     

Synthesis and characterization of poly(lactic acid) and aliphatic polycarbonate copolymers

BACKGROUND: Poly(lactic acid) (PLA) has received much attention as a biodegradable polymer. But the physical properties of PLA, such as brittleness, limit its wider applicability. Copolymerization polymers ing soft blocks provides a useful method to improve the mechanical properties of PLA. RESULTS: Poly(lactic acid)‐block‐(polycarbonate diol) (PLA‐PCD) copolymers were synthesized using a two‐step process with polycondensation and chain extension reactions. The effect of polycarbonate diol content on the prepolymer properties was studied. The chain‐extended products were characterized using ¹H NMR, F and. The effect of the NCO/OH ratio on the properties of the chain‐extended products, including the mechanical properties and thermal properties, was studied. eight‐average molecular weight of the product can reach 210 000 g mol^?1 when the molar ratio of ? NCO to ? OH is 3:1. CONCLUSION: The PLA‐PCD copolymers obtained can crystallize, and the crystallinity decreases with chain‐extension reaction. The products exhibit superior mechanical properties with elongation at break above 230%, which is much higher than that of PLA chain‐extended products. The products have a good potential for packaging applications. Copyright © 2009 Society of Chemical Industry     

The influence of knit-lines on the tensile properties of fiberglass reinforced thermoplastics

The adverse effect of knit-line formation on the mechanical properties of thermoplastics has been well documented for unfilled materials. A majority of these investigations concern amorphous polymers, whereas a number of engineering polymers are semicrystalline and also contain reinforcing fillers and fibers. The present investigation deals with the effect of knit-lines on the mechanical behavior of unfilled and glass fiber-reinforced semicrystalline polymers, such as polypropylene, poly(butylene terephthalate), poly(ethylene terephthalate), and poly(phenylene sulfide). Unfilled and fiber-reinforced polystyrene was also investigated for reference. Tensile specimens with knit-lines were produced by impinging melt fronts from two gates located at opposite ends of the dumbbell-shaped mold. The effect of process conditions on the knit-line strength was studied by varying primarily the melt and mold temperatures. The presence of glass fibers significantly reduced the knit-line factor based on strength and strain to failure for the reinforced grades of all polymers relative to their respective unfilled grades. This is attributed to the lack of fiber flow across the knit-line, which makes the material in the knit-line region act as if it is not reinforced. The knit-line strength could be changed through process modifications. For the unfilled grades of semicrystalline polymers, the presence of knit-lines did not affect the yield strength but reduced the elongation at onset of necking, indicating that little spherulitic growth takes place across the knit-line.     

HDPE/LLDPE reactor blends with bimodal microstructures—Part II: rheological properties

Reactor blends of polyethylene/poly(ethylene-co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and vice versa HMW homopolymer to LMW copolymer. The shear flow characteristics of these polymers in the typical processing range mostly depend on the molecular weight and MWD of the polymer and are independent of the short chain branch content. From oscillatory shear measurements, it was observed that the viscosity of HMW polymers was reduced with the addition of LMW material. For the polymers produced with this two-step polymerization process, the LMW homopolymer and HMW copolymer blends and HMW homopolymer and LMW copolymer blends were melt miscible, despite the large viscosity differences of the pure components.     

Thermoplastic biodegradable material elaborated from unripe banana flour reinforced with metallocene catalyzed polyethylene

To meet the challenge of procuring new sources of natural polymers without affecting the demands for food crops, a thermoplastic unripe banana flour (TPF) was produced, characterized, and blended with metallocene‐catalyzed polyethylene (mPE). Both the pulp and peels of unripe banana were used to produce flour, whose stability and thermoplastic properties allowed blending with mPE in high proportions, that is, 50, 60, 70, and 80%. The blends were injection molded, and the thermal, mechanical, microstructural, and infrared spectral properties of the resulting samples were characterized. The blend containing 50% TPF yielded a robust, elastic, and nonbrittle material. Maleic anhydride grafting on mPE (mPE‐g‐MA) promoted interphase adhesion of the polymers and homogeneity in the blends. Grafting also influenced the mechanical, thermal, and microstructural properties of the blends. The characteristics of the blends make them ideal for designing biodegradable plastics while exploiting banana peels, which are usually considered agricultural waste. POLYM. ENG. SCI., 55:866–876, 2015. © 2014 Society of Plastics Engineers     

Characterization of mouthguard materials: A comparison of a commercial material to a novel thiolene family

The goal of this study is to compare the thermal and mechanical properties of a commercial mouthguard material with a novel class of thermoset polymers based on thiolene “click” chemistry. Ternary thiolene systems modified with urethane or acrylate [urethane‐modified thiolene network (UMTEN) and acrylate‐modified thiolene network (AMTEN), respectively] were synthesized and their properties compared with commercially available Polyshok™. Durometer hardness (ASTM D2240‐05), water absorption [ASTM D570‐98 (2005)], tear strength (ASTM D624‐00), and impact attenuation [ASTM D6110‐06f (modified)] were measured for physical property comparison. Differential scanning calorimetry and dynamic mechanical analysis were used as a means to compare thermal properties. One‐way analysis of variance and independent t tests were used to test for differences between Polyshok™, AMTEN and UMTEN samples. It was found that the novel thiolene networks exhibit higher impact attenuation at intraoral temperature compared with Polyshok™, although Polyshok™ demonstrates lower water absorption and hardness, as well as higher tear strength. With further modification, this family of thiolene materials may provide a platform for developing next‐generation mouthguard materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40402.     

Plasma treatment‐induced fluorine‐functionalized multi‐walled carbon nanotubes to modify poly(ethylene terephthalate) obtained via in situ polymerization

The introduction of carbon nanotubes in a polymer matrix can markedly improve its mechanical properties and electrical conductivity, and much effort has been devoted to achieve homogeneous dispersions of carbon nanotubes in various polymers. Our group previously performed successfully fluorine‐grafted modification on the sidewalls of multi‐walled carbon nanotubes (MWCNTs), using homemade equipment for CF₄ plasma irradiation. As a continuation of our previous work, in the present study CF₄ plasma‐treated MWCNTs (F‐MWCNTs) were used as a nanofiller with poly(ethylene terephthalate) (PET), which is a practical example of the application of such F‐MWCNTs to prepare polyester/MWCNTs nanocomposites with ideal nanoscale structure and excellent properties. As confirmed from scanning electron microscopy observations, the F‐MWCNTs could easily be homogeneously dispersed in the PET matrix during the in situ polymerization preparation process. It was found that a very low content of F‐MWCNTs dramatically altered the crystallization behavior and mechanical properties of the nanocomposites. For example, a 15 °C increase in crystallization temperature was achieved by adding only 0.01 wt% F‐MWCNTs, implying that the well‐dispersed F‐MWCNTs act as highly effective nucleating agents to initiate PET crystallization at high temperature. Meanwhile, an abnormal phenomenon was found in that the melt point of the nanocomposites is lower than that of the pure PET. The mechanism of the tailoring of the properties of PET resin by incorporation of F‐MWCNTs is discussed, based on structure–property relationships. The good dispersion of the F‐MWCNTs and strong interfacial interaction between matrix and nanofiller are responsible for the improvement in mechanical properties and high nucleating efficiency. The abnormal melting behavior is attributed to the recrystallization transition of PET occurring at the early stage of crystal melting being retarded on incorporation of F‐MWCNTs. Copyright © 2009 Society of Chemical Industry     

Regulating the Interface in Graphite/Thermoplastic Composites

Among the many engineering thermoplastics available today, there exists a large subgroup of difficult-to-crystallize or amorphous polymers which possess a rather unique micronodular morphology in their normally produced solid state. When these polymers are processed in the unfilled state, changes in process thermal history have little effect on mechanical properties; but when reinforcement such as graphite is added, pronounced effects of thermal treatment arise which are relatable to the nodular polymer morphology. These effects will be documented and explained for graphite fiber-filled polycarbonate and poly(phenylene oxide). The practical application of these results to hot-forming techniques will also be described. Finally, extension of these techniques to the more easily crystallized thermoplastics such as polypropylene will be considered.     

Optimierende reaktionsführung lebender polymerer. Darstellung von produkten mit bimodalen molekulargewichtsverteilungsfunktionen im rohrreaktor

Polymers with bimodal molecular weight distributions are remarkable for advantageous cold flow properties and good manufacturing. Using polyreaction of isoprene with n-butyllithium in n-heptane as an example for polyreactions of living polymers, for a tubular flow reactor with double initiator infusion a procedure is described which permits to precalculate optimal values of control variables used for the production of polymers which have required bimodal molecular weight distributions. The analysis of thus produced polymers by ultracentrifugal measurements shows an excellent agreement of theoretical and practical molecular weight distributions.     

Dynamic mechanical behavior and nanostructure morphology of hyperbranched‐modified polypropylene blends

Polypropylene (PP) was modified utilizing two types of polyesteramide‐based hyperbranched polymers (amphiphilic PS and hydrophilic PH). A maleicanhydride‐modified PP (PM) was used as a reactive dispersing agent to enhance the modification by grafting the hyperbranched polymers onto the PP chains. Pure PP, two different non‐reactively modified samples, i.e. excluding PM, and two different reactively modified samples, i.e. including PM, were studied. Investigating the morphology of the samples was performed by scanning electron microscopy. To follow the effect of the modification on the dynamic mechanical properties, dynamic mechanical analysis experiments both in the melt (rheometric mechanical spectrometry) and in solid state (dynamic mechanical thermal analysis) were carried out. In the next step, the nanocrystalline structure of the samples was studied by small angle X‐ray scattering (SAXS) in two different modes, i.e. static and recrystallization. Hundreds of SAXS patterns were analyzed automatically using procedures written in PV‐WAVE image‐processing software. The chord distribution function (CDF) was calculated and the long period (l_p) of the crystal lamellae was extracted from the CDFs. The rheometric mechanical spectrometry results show that both hyperbranched polymers decrease complex viscosity η^* and enhance liquid‐like behavior. This happens more significantly when PM is included. The dynamic mechanical thermal analysis results reveal that T_g decreases when PS and PH are added. In the reactively modified samples this reduction is compensated most probably because of the crosslinked structure formed through the grafting reaction between the hyperbranched polymers and PM. Such structure is confirmed by SAXS data and calculated CDFs in the recrystallization mode. Static SAXS data also show enhancement in the crosshatched morphology of the crystalline lamellae of PP for reactively modified samples compared with non‐reactively modified samples. © 2013 Society of Chemical Industry     

Pultruded fiber reinforced blocked polyurethane (PU) composites. II. Processing variables and dynamic mechanical properties

Unidirectional fiber reinforced blocked polyurethane (PU) composites have been prepared by the pultrusion process. The effects of processing variables on the mechanical properties and dynamic mechanical properties of fiber reinforced PU composites by pultrusion have been studied. The processing variables investigated included pulling rate (in-line speed), die temperature, postcure time and temperature, and filler type and content. The dynamic mechanical properties of the composites produced by the process were studied utilizing dynamic mechanical spectrometer. Results show that the composites possessed various optimum pulling rates at different die temperatures. From the DSC data analysis, swelling ratio, and mechanical properties, the optimum die temperature was determined. It was found that the mechanical properties increase with filler content for various types of filler. The increasing of mechanical properties depends on the optimum postcure temperature and time. However, the properties decreased for longer postcure times since the composite materials were degraded. The glass-transition temperature (T_g) increased slightly and the damping peak (tan δ) was broadened due to fiber reinforcement. The dynamic mechanical moduli (G′, G″) of pultruded PU composites are apparently higher than those of the matrices. The moduli (G′, G″) increase with increasing fiber and filler content, and the damping peak becomes broad. Effect of postcuring on the degree of crosslinking, T_g, and dynamic modulus will be discussed.