Addition Of Hyperbranched Polymers Research Articles

Synergistic improvement of epoxy composites with multi-walled carbon nanotubes and hyperbranched polymers

This paper presented the preparation of composites that consist of multi-walled carbon nanotubes (MWCNTs), hyperbranched polymers (HBPs), epoxy resins (EP) and curing agent. The influences of HBPs and MWCNTs content on the curing process of epoxy systems and mechanical performances of MWCNTs/HBPs/EP composites were discussed. Results from differential scanning calorimeter (DSC), tensile, impact and toughness tests are provided. The tensile and impact fracture surface were observed by field-emission scanning electron microscopy. The addition of HBPs resulted in accelerating the curing process of epoxy systems. MWCNTs/HBPs/EP composites were capable of increasing tensile strength by up to 38%, giving a tensile modulus of 25%, impact strength of 68%, fracture toughness of 66%, and a glass transition temperature (Tg) of 46% in comparison with unmodified epoxy thermosets. Field emission-scanning electron micrographs showed that these increases were associated with a synergistic effect of plastic deformation mechanism and crack pinning mechanism, which were induced by the present of HBPs and MWCNTs, respectively.

An investigation of the impact of an amino-ended hyperbranched polymer as a new type of modifier on the compatibility of PLA/PBAT blends

Abstract Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends using amino-ended hyperbranched polymers (HBP) as modifiers were prepared by melt-mixing through a double-roller mill and injection molding. It was found that when the content of HBP was 2.5 phr, the elongation at break and the impact strength of PLA/PBAT blends both reached peak values. Moreover, by addition of HBP, the ΔTg of the blends was smaller. These results, together with Scanning electron microscope (SEM) images on the fractured morphology of the blends, indicate that the compatibility between PLA and PBAT is improved upon addition of HBP. The mechanism of the impact of HBP on the improvement of the compatibility between PLA and PBAT is proposed based upon Fourier transform infrared (FTIR) spectra.

Studying the effect of hyperbranched polymer modification on the kinetics of curing reactions and physical/mechanical properties of UV-curable coatings

Abstract A polyester-amide based hyperbranched polymer with hydroxyl end-groups is modified by the aid of acrylic functionalities. Two levels of modification, i.e. 40% and 65%, are considered. The unmodified hyperbranched polymer and the modified ones are added to UV-curable monomeric and oligomeric systems. Rheology measurements are conducted to investigate the effects of hyperbranched polymer on the rheological behavior. In order to assess the curing kinetics and physical/mechanical characteristics of the samples, photo-DSC and DMA experiments are exploited, respectively. The effect of viscosity and number of UV-curable functionalities of the hyperbranched polymer on the curing level and kinetics of the curing reactions are discussed. Dynamic mechanical analysis shows that the addition of hyperbranched polymer in the formulation increases a 25% in storage modulus of the glassy region and cross-linking density of the UV-curable coating. Furthermore, it is also seen that the existence of the hyperbranched polymer increases the viscosity of Trimethylolpropane triacrylate (TMPTA)-based system while it is decreasing the viscosity of oligomeric-based of the epoxy di-acrylate system. It is obtained that the hyperbranched polymer makes the curing level in the monomeric and the oligomeric system, improve up to 15% and 10% correspondingly. It is also observed that T g s of the coatings containing the hyperbranched polymer increases up to 5.9 °C.

The chemo-rheological behavior of an acrylic based UV-curable inkjet ink: Effect of surface chemistry for hyperbranched polymers

Abstract A polyester-amid based hyperbranched polymer (HBP) with hydroxyl terminal groups is modified by the aid of saturated fatty acid groups with 7 carbon lengths. FTIR results reveal that about 85% of hydroxyl terminal groups were replaced by fatty acid chains. Having prepared and characterized the inferred modified HBP, the effect of both neat and modified forms of HBP was tested on the curing behavior of an acrylic based UV-curable inkjet ink by time-resolving photo rheo-mechanical spectroscopy (TRP-RMS). The chemo-rheological results of TRP-RMS show that the hyperbranched polymers, in both neat and modified forms affected the rheological behavior of the ink during the curing process. In this research, slope of estimated line on the chemo-rheological curves was used to measure the rate of complex viscosity growth of ink formulation during the curing process. Accordingly, slope in the blend without HBPs was 180.56 Pa and it increased to about 300 Pa on addition of HBPs even at a loading of as much as 2 wt.%. Results demonstrate that hyperbranched polymers have altering influence at the various different stages of the curing process.

Isothermal crystallization kinetics of AB2 hyper-branched polymer (HBP)-filled polypropylene (PP)

In this paper, the isothermal crystallization kinetics of pure polypropylene (PP) and AB2 hyper-branched polymer (HBP)/PP blends have been investigated by differential scanning calorimetry (DSC). During isothermal crystallization, the crystallization rates of the blends are higher than those of PP. Furthermore, in the blends with different HBP contents, the value of t 1/2 became smaller with increasing HBP content; however, the crystallization rate of the blend decreased slightly when the content of HBP is 5 %. An increase in the Avrami exponent means the addition of HBP influences the mechanism of nucleation and the growth of PP crystallites. In addition, the crystallization activation energy of pure PP and HBP/PP blends were also discussed, and the result showed that the crystallization activation energy has decreased remarkably in HBP/PP blends.

Nonisothermal crystallization kinetics of AB2 hyperbranched polymer‐filled polypropylene

In this article, nonisothermal crystallization kinetics of polypropylene (PP) and AB2 hyperbranched polymer (HBP)‐filled PP have been investigated by differential scanning calorimetry. The Avrami analysis modified by Mandelkern and a method combined with Avrami and Ozawa equations were employed to describe successfully the nonisothermal crystallization kinetics of samples. The conclusion showed that HBP can prompt crystallization effectively. Furthermore, in blends of different HBP contents, the value of t1/2 became smaller with increasing HBP content; however, the crystallization rate of the blend decreased slightly when content of HBP is 5%. An increase in the Avrami exponent showed that addition of HBP influenced the mechanism of nucleation and the growth of PP crystallites. The possible explanation could be attributed to the fractal structure of HBP. The polarized micrographs showed that HBP acts as a heterogeneous nucleation agent, and the nucleation efficiency has increased remarkably in HBP/PP blends. POLYM. ENG. SCI., 53:2535–2540, 2013. © 2013 Society of Plastics Engineers

Benefits and Limitations of Adding Hyperbranched Polymers to Dental Resins

Volumetric shrinkage reduction is a constant challenge in the improvement of dental resins. The inclusion of hyperbranched polymers (HBPs) with modified functionalities (hydroxyl, propionate, and methacrylate) instead of conventional dimethacrylate monomers has the potential to reduce shrinkage, but can also affect other properties. The null hypothesis was that the addition of HBPs (from 5 to 40 mass%) to a 50/50 mass% Bis-GMA/TEGDMA mixture reduces shrinkage without affecting degree of conversion, elastic modulus, glass transition temperature, Wallace hardness (before/after ethanol storage), and viscosity. This hypothesis was rejected, since HBP incorporation significantly affected most properties either negatively or positively. When HBP amounts in the resin were increased, the following general trends were observed: Volumetric shrinkage decreased significantly (p < 0.0001), down to about one-third of the control value at 40% HBP; Wallace hardness (both before and after ethanol) and viscosity increased progressively, while elastic modulus showed a parabolic profile, with a maximum at 10% HBP; and finally, degree of conversion and glass transition temperature were relatively stable, regardless of the HBP content. These results indicate that HBPs with modified end groups might be interesting substitutes for Bis-GMA/TEGDMA.

Effect of Hyperbranched Polymer on Crystallization Kinetics of Isotactic Polypropylene

In this paper, the isothermal crystallization kinetics of isotactic polypropylene (iPP) and iPP with 5% hyperbranched polymer (HBP) added had been investigated by differential scanning calorimetry (DSC). The results show that a small addition of HBP affects the crystallization behavior of iPP. During isothermal crystallization, the crystallization rate of the blend is higher than those of iPP remarkably. An increase in the Avrami exponent may be attributed to the fractal structure of hyperbranched polymer. The crystallization activation energy is estimated by the Friedman equation, the results show that the activation energy decreases remarkably by addition of HBP and the crystallization rate of the blend is more sensitive to temperature than that of iPP.

Processing of poly(hydroxybutyrate-co-hydroxyvalerate)-based bionanocomposite foams using supercritical fluids

Abstract

Microcellular poly(hydroxybutyrate‐co‐hydroxyvalerate)‐hyperbranched polymer–nanoclay nanocomposites

AbstractThe effects of incorporating hyperbranched polymers (HBPs) and different nanoclays [Cloisite® 30B and halloysite nanotubes (HNT)] on the mechanical, morphological, and thermal properties of solid and microcellular poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) were investigated. According to the X‐ray diffraction (XRD) and transmission electron microscopy (TEM) analyses, Cloisite 30B exhibited a combination of exfoliation and heterogeneous intercalation structure for both solid and microcellular PHBV–12% HBP–2% Cloisite 30B nanocomposites. TEM images indicated that HNTs were uniformly dispersed throughout the PHBV matrix. The addition of 2% nanoclays improved the thermal stability of the resulting nanocomposites. The addition of HBP+poly(maleic anhydride‐alt‐1‐octadecene) (PA), Cloisite 30B, and HNT reduced the average cell size and increased the cell density of the microcellular components. The addition of (HBP+PA), Cloisite 30B, and HNT also increased the degree of crystallinity for both solid and microcellular components in comparison with neat PHBV. Also, with the addition of 12% (HBP+PA), the area under the tan‐δ curve, specific toughness, and strain‐at‐break of the PHBV–HBP nanocomposite increased significantly for both solid and microcellular specimens, whereas the storage modulus, specific Young's modulus, and specific tensile strength decreased. The addition of 2% nanoclays into the PHBV–HBP nanocomposites improved the storage modulus, specific Young's modulus, and specific tensile strength of the PHBV–HBP–nanoclay‐based nanocomposites, but they were still lower than those of the neat PHBV. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Scratch resistant tough nanocomposite epoxy coatings based on hyperbranched polyesters

Advanced multifunctional coatings were prepared by UV curing of epoxy based formulations containing hyperbranched polymers (HBP) and an epoxy functionalized alkoxysilane additive. The addition of HBP to the UV curable epoxy resin induced an important flexibilization of the glassy epoxy network with an increase in toughness of the cured polymeric coatings. Adding the functionalized alkoxysilane into the UV curable formulations, as inorganic precursor of silica phase, an improvement on surface hardness was obtained without strongly affecting the flexibilization and the toughness achieved by the addition of the HBP additive. The increase on surface hardness was accompanied with an increase in scratch resistance and modulus. Advanced scratch resistant and tough nanocomposite epoxy coatings were obtained by properly selecting the components of the formulation.

Physical and mechanical properties of dental nanocomposites composed of aliphatic epoxy resin and epoxidized aromatic hyperbranched polymers

AbstractAliphatic epoxy resin (UVR6105) and epoxidized aromatic hyperbranched polymers (HBP) were used as dental resin matrixes, siliane‐treated inorganic nanoparticles as inorganic fillers, ethyl 4‐dimethylaminobenzoate, camphorquinone, and 4‐[(2‐hydroxytetradecyl)oxy] phenyl‐phenyliodoniumhexafluoroantimonate (CD1012) as initiators to formulate new kinds of dental nanocomposites. Their physical and mechanical properties were tested and the inner structure was observed by using scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The 7 series thermal analysis system was used to determine the glass transition temperature of dental resins. Compressive strengths of dental nanocomposites are lower, diametral tensile strengths are comparable with, flexural strengths are higher than those of commercial hybrid composite (Spectrum‐TPH). The addition of HBP decreased the glass transition temperature of aliphatic epoxy resin. SEM photo micrograph shows that the nanoparticles were well dispersed and inlayed in the resin matrixes. TEM photo micrograph shows that the inner structure of dental resins presents club‐shaped. Epoxidized aromatic hyperbranched polymer can strengthen and toughen aliphatic epoxy resin. These nanocomposites are potential for dental application. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Influence of an hyperbranched aliphatic polyester on the cure kinetic of a trifunctional epoxy resin

AbstractThe influence of an OH‐terminated hyperbranched aliphatic polyester on the reaction kinetics and rheology of a trifunctional triglycidyl‐p‐aminophenol (TGAP) epoxy resin cured with an aromatic amine, i.e., diamino‐diethyltoluene (DETDA), was investigated. The hyperbranched polymer was expected to enhance the reactivity of the trifunctional epoxy resin; a limited modification in the rheology of the trifunctional epoxy resin with the addition of the hyperbranched polymer, however, was not excluded. The reaction mechanism between DETDA amine and TGAP resin is very complex; therefore, a phenomenological kinetic model was employed. The autocatalytic model chosen was able to fit the experimental calorimetric data for the trifunctional epoxy resin as well as for its mixtures with the hyperbranched polymer. The effect of the OH‐terminated hyperbranched aliphatic polyester (H 30) on the reactivity of the trifunctional epoxy resin was marked, with a decrease of the temperatures at which the crosslinking reactions begin, even though a reduced rate of the curing reactions was observed. However, the completion of the reactions occurred faster and at lower temperatures. The cure mechanism, moreover, remained broadly autocatalytic in nature, regardless of H 30 concentration. Finally, the addition of hyperbranched polymer H 30, even at low percentages, led to a noticeable increase in the viscosity of the resin. This last aspect is believed to restrict to some extent the range of application of such epoxy systems containing the hyperbranched polymer in the traditional processing techniques. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Mechanical Behavior and Fracture Toughness of Poly(L‐lactic acid)‐Natural Fiber Composites Modified with Hyperbranched Polymers

AbstractSummary: The use of hyperbranched polymers (HBP) with hydroxy functionality as modifiers for poly(L‐lactic acid) (PLLA)‐flax fiber composites is presented. HBP concentrations were varied from 0 to 50% v/v and the static and dynamic tensile properties were investigated along with interlaminar fracture toughness. Upon addition of HBP, the tensile modulus and dynamic storage modulus (E′) both diminished, although a greater decline was noticed in the static modulus. The elongation of the composites with HBP showed a pronounced increase as large as 314% at 50% v/v HBP. The loss factor (tan δ) indicated a lowering of the glass transition temperature (Tg) due to a change in crystal morphology from large, mixed perfection spherulites to finer, smaller spherulites. The change in Tg could have also resulted from some of the HBP being miscible in the amorphous phase, which caused a plasticizing effect of the PLLA. The interlaminar fracture toughness measured as the critical strain energy release rate (GIC) was significantly influenced by HBP. At 10% v/v HBP, GIC was at least double that of the unmodified composite and a rise as great as 250% was achieved with 50% v/v. The main factor contributing to high fracture toughness in this study was better wetting of the fibers by the matrix when the HBP was present. With improved ductility of the matrix, it caused ductile tearing along the fiber‐matrix interface during crack propagation.ESEM photograph of propagation region of the interlaminar fracture toughness specimens with 30% v/v of HBP.imageESEM photograph of propagation region of the interlaminar fracture toughness specimens with 30% v/v of HBP.

Toughening of trifunctional epoxy using an epoxy‐functionalized hyperbranched polymer

AbstractChemorheology of curing as well as the phase separation behavior of an epoxy‐functionalized hyperbranched polymer (HBP)‐modified triglycidyl p‐amino phenol (TGAP) epoxy mixtures has been studied by several techniques. There was little change in gel time as a result of addition of HBP up to 10% of HBP, even though the HBP reacts at a slower rate with amine hardeners compared to the TGAP alone. The thermal and dynamic viscoelastic behavior of the modified matrices have been examined and compared with the unmodified TGAP matrix. Finally, impact properties have been discussed in terms of the morphological behavior for a TGAP matrix modified with various amounts of HBP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2339–2345, 2003

Studies on blends of epoxy-functionalized hyperbranched polymer and epoxy resin

An epoxy-functionalized hyperbranched polymer (HBP) was used to toughen a conventional epoxy resin, diglycidyl ether of bisphenol A (DGEBA) cured with diethyltoluene-2,6-diamine (DETDA). There was little change in gel time as a result of addition of HBP, even though the HBP reacts at a slower rate with amine hardeners compared to DGEBA alone. Phase separation was investigated for various HBP contents and as a function of cure conditions as well. The thermal and dynamic viscoelastic behavior of the modified matrices have been examined and compared to the DGEBA epoxy matrix. It appears that the HBP which phase separates does not react as fully as when it is reacted with the amine alone. Nonetheless, good improvement in impact strength as a result of incorporation of HBP were observed and explained in terms of morphological behavior for a DGEBA matrix modified with various amounts of HBP.

Film blowing of linear low-density polyethylene blended with a novel hyperbranched polymer processing aid

The use of hyperbranched polymer (HBP) as a processing aid for linear low-density polyethylene (LLDPE) in the tubular film blowing process was investigated. Through the addition of HBP, sharkskin was successfully eliminated without significantly changing the overall physical properties of LLDPE films. Also, there was a minimum of 40% enhancement in processing rate with addition of 0.5wt% HBP. The study showed that HBP and LLDPE are immiscible, and HBP has a tendency to migrate to the surface, subsequently, it seems to form a lubricating layer between the metal surfaces and the bulk material. This phase separation between HBP and LLDPE results in an HBP-rich surface, which has a high potential to create unique surface properties tailored to various applications. Rheological analysis indicated that excessive slip was present in HBP/LLDPE suggesting that the onset of slip is not the cause of sharkskin. On the contrary, it may be partially responsible for the elimination of sharkskin.