Crystallization of post-consumer polypropylene in the presence of β-nucleating agent

Journal of Thermal Analysis and Calorimetry - In this paper, the heat transfer characteristics of the nanofluid through a parallel plate soft nanochannel are investigated under the fully developed...     

Thermal behavior of isotactic polypropylene in different content of β-nucleating agent

The effects of non-isothermal and isothermal crystallization on the formation of α- and β-phase in isotactic polypropylene (iPP) with different content of β-nucleating agent are investigated by differential scanning calorimetry (DSC). On non-isothermal crystallization, the content of β-phase and regularity of its crystals are depended on both cooling rate and the content of β-nucleating agent. The faster cooling rate is, the lower of melting peak temperature (T_mp) and crystallization peak temperature (T_cp) of α- and β-phase are. The enthalpy of fusion (∆H) of β-phase increases with cooling rate in a certain range for the sample with 0.1 wt% β-nucleating agent (G₁) and decreases for that with 0.3 wt% β-nucleating agent (G₃). On isothermal crystallization, the enthalpy of fusion of β-phase in G₁ is higher than in G₃ which is related to the efficiency of nucleation in different concentration of nucleating center in two samples.     

Thermal stability of nucleation effect of different β-nucleating agents in isotactic polypropylene

Journal of Thermal Analysis and Calorimetry - The thermal stability of nucleation effect of three highly effective β-nucleating agents, namely an aryl diamide-based nucleating agent (TMB-5), a...     

The enhanced nucleating ability of carbon nanotube-supported β-nucleating agent in isotactic polypropylene

A kind of β-nucleating agent, calcium pimelate, for polypropylene (PP) was chemically supported onto the surface of multi-wall carbon nanotubes, and the effect of the multi-wall carbon nanotube-supported β-nucleating agent on the mechanical properties and morphology of isotactic polypropylene composites was investigated. The composites of isotactic polypropylene and multi-wall carbon nanotube-supported β-nucleating agent exhibited excellent impact toughness compared with pure isotactic polypropylene and β-nucleated isotactic polypropylene, being more than seven times over that of pure isotactic polypropylene and more than three times over that of β-nucleated isotactic polypropylene. The excellent impact behaviors of the composites were also evidenced by the fracture morphology based on scanning electron microscopy observations. Differential scanning calorimetry and wide-angle X-ray diffraction results verified the enhanced nucleating ability of the multi-wall carbon nanotube-supported β-nucleating agent, which greatly improved the impact toughness without significantly deteriorating the strength and stiffness of the polypropylene composites.     

Effect of β-nucleating agent on crystallization of wollastonite-filled recycled polypropylene composites

Journal of Thermal Analysis and Calorimetry - The crystallization behavior, melting characteristics, and semicrystalline morphologies of wollastonite-filled recycled polypropylene (R-PP) composites...     

Synergistic nucleation effect of calcium sulfate whisker and β-nucleating agent dicyclohexyl-terephthalamide in isotactic polypropylene

Journal of Thermal Analysis and Calorimetry - The crystallization and melting behaviors and mechanical properties of isotactic polypropylene (iPP) containing a certain amount of stearic...     

The β-nucleation of polypropylene random copolymer filled by nano-CaCO3 supported β-nucleating agent

In this article, ??-nucleation of nano-CaCO₃ (CC) supported ??-nucleating agent (Sup-??-NA) for random polypropylene copolymer (PPC) crystallization was studied by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. The results showed that Sup-??-NA not only increased the peak temperature of the crystallization of PPC but also induced PPC to form almost pure ??-modification. It indicated that Sup-??-NA possessed effective ??-nucleation. The content of Sup-??-NA had little influence on the crystallization behavior and melting characteristics together with the ??-modification content of PPC, but those were affected by the mass ratio of CC/??-NA (calcium pimelate) in the Sup-??-NA. The final temperature of the melt between 300 and 180?°C did not affect the ??-nucleation of Sup-??-NA, although the ??-nucleation of Sup-??-NA would be decreased with the final temperature of the melt lower than 170?°C. In addition, DSC multiple heating and cooling scanning had little influence on the thermal stability of ??-nucleation of Sup-??-NA.     

Preparation and characteristics of nano-CaCO3 supported β-nucleating agent of polypropylene

In this paper, nano-CaCO₃ supported β-nucleating agent for polypropylene (PP) was prepared by supporting pimelic acid on nano-CaCO₃ with two methods. The thermal properties of pimelic acid and nano-CaCO₃ supported β-nucleating agent were investigated by differential scanning calorimetry and thermogravimetry coupled with Fourier transform infrared spectrometry. The results indicated that the formation of β-nucleating agent supported on nano-CaCO₃ was attributed to the chemical reaction between nano-CaCO₃ and pimelic acid. The β-nucleating agent was added to PP to examine its β-nucleating ability for PP, the polymorphism of the PP was characterized by wide-angle X-ray diffractometer. The results of investigation showed that the nano-CaCO₃ supported β-nucleating agent exhibited higher nucleation ability and lower price compared to calcium pimelate β-nucleating agent.     

Nonisothermal crystallization kinetics of isotactic polypropylene nucleated with a novel supported β-nucleating agent

The introduction of β-nucleating agent into isotactic polypropylene (iPP) is the most effective method to prepare β-iPP. In this paper, iPP nucleated with a novel highly efficient supported β-nucleating agent (NA100), calcium pimelate (CaHA) supported on the surface of nano-CaCO₃, was prepared and its nonisothermal crystallization kinetic, melting characteristic, and crystallization activation energy are investigated and compared with those of pure iPP, nano-CaCO₃ filled iPP, and β-nucleating agent CaHA nucleated iPP. The results indicate that addition of nano-CaCO₃ increases the crystallization temperature of iPP and has no influence on the crystal form of iPP. iPP and nano-CaCO₃ filled iPP mainly crystallize in the form of α-crystal. Although NA100 and CaHA induce iPP to mainly form β-crystal, NA100 nucleated iPP shows higher crystallization temperature, melting temperature, and β-phase content than that nucleated with CaHA without supports. Nonisothermal crystallization kinetic is well described by the equations of Avrami and Mo, and the crystallization activation energy was calculated from Kissinger’s method. It was found that the decreased crystallization activation energy is favorable to increase the crystallization rate and the content of β-crystal. Although the content of CaHA in 5 wt% NA100 nucleated iPP was less than that in 0.1 wt% CaHA nucleated iPP, the former formed more β-iPP than the latter, indicating that the β-nucleating agent CaHA supported on the surface of nano-CaCO₃ exhibits higher efficiency for preparation of β-iPP than pure CaHA powder.     

Kinetics of peroxidase-catalyzed oxidation of quercetin in the presence of β-cyclodextrin

It is established that the rate of peroxidase-catalyzed oxidation of flavonoid quercetin is increased by 20% in the presence of macrocyclic complexing agent β-cyclodextrin. The comparison of the kinetic parameters of the indicated reaction in the presence and in the absence of β-cyclodextrin shows that its introduction does not significantly influence the specificity of the enzyme with respect to the reducing substrate (characterized as k _cat/K _M ratio), while the increase in the reaction rate does not depend on the duration of the incubation of quercetin with β-cyclodextrin. It is assumed that the increase of the reaction rate is associated with nonspecific interaction between β-cyclodextrin and quercetin oxidation product.     

Synergistic toughening effect of β-nucleating agent and long chain branching on polypropylene random copolymer

β-nucleated long chain branched (LCB) polypropylene random copolymers (PPRs) were prepared via reactive extrusion by introducing β nucleating agent (NA), dicumyl peroxide (DCP) and various contents of 1, 6-Hexanediol diacrylate (HDDA) into PPR. Results of Fourier infrared spectroscopy (FTIR) and the rheological properties demonstrate the existence of LCB polypropylene. Mechanical properties including impact strength, tensile strength and elongation at break were studied. The crystal structure, morphology and crystallization behavior were investigated via wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM) and differential scanning calorimetry (DSC). Non-isothermal crystallization kinetics using the Jeziorny method was also studied. The results show an increased LCB degree with increasing HDDA amount. For the sample with a moderate LCB level, synergistic toughening effect of NA and LCB is achieved without deterioration of yield strength or elongation at break, partially because of its higher β-phase content and much smaller spherulite size. It exhibits the minimum values of T_c and Z_c1, and the maximum values of t_1/2 and n₁ in the primary stage of crystallization, regardless of the cooling rate, indicating a slower crystallization rate and more complicated nucleation and crystal growth model.     

The synergistic effects of β-nucleating agent and ethylene–octene copolymer on toughening isotactic polypropylene

The mechanical properties of isotactic polypropylene (iPP) and ethylene–octene copolymer (POE) blends with or without β-nucleating agent (β-NA) were systematically studied. Results demonstrated that, after β-NA and POE were separately added, the impact strength of injection molded iPP samples increased. β-NA and POE were also found to have a synergistic toughening effect on iPP matrix, and the effect was significant. When the contents were 0.05 wt% β-NA and 10 wt% POE, the impact strength reached the maximum, i.e., almost 15 times that of neat iPP. SEM further revealed that POE in skin and core layers existed as long and narrow strips along the flow direction and throughout crystals. The tensile strength did not deteriorate because of the special phase morphology and tight interfacial interaction between POE phase and matrix. WAXD and DSC revealed that POE addition had negligible influence on crystal form, and a considerable number of β crystals was generated by adding β-NA. SEM results also confirmed a critical β-NA content. When β-NA content was lower than the critical value, perfect β sphaerocrystals were generated. When β-NA was higher, “bundle-like” crystal structures formed. Perfect β sphaerocrystals were more efficient for dissipating energy because of the looser stacking pattern, thus showing better toughness.     

Combined effect of β-nucleating agent and multi-walled carbon nanotubes on polymorphic composition and morphology of isotactic polypropylene

The effects of nucleating duality, imposed by a mixed nucleating agent (NA) system containing multi-walled carbon nanotubes (MWCNTs) and a rare earth (WBG), on the crystallization behaviors of isotactic polypropylene (iPP) including the peak temperature of crystallization (T _cp), polymorphic composition, and crystalline morphology, were probed in detail by calorimetry, X-ray diffraction, and polarized light microscopy. In such mixed nucleating agent system, MWCNTs is active filler to induce α-nucleation for iPP, while WBG serves as β-nucleating agent. When the WBG content was low (0.05%), the crystals of WBG were as a form of individual isotropic dendrite, and the enhancement of T _cp was achieved by the incorporation of MWCNTs. As the WBG content was high as 0.1%, a percolated NA network consisted of needlelike crystals of WBG yielded before nucleating the prevalent crystallization of iPP. In this case, the addition of MWCNTs has no obvious effect on T _cp. However, by varying the mass proportion of MWCNTs/WBG, the polymorphic composition was adjusted significantly, indicating a nucleation competition between MWCNTs and WBG. Although the competitive growth existed between α-crystals nucleated by MWCNTs and β-crystals nucleated by WBG, the formation of primary β-crystallite was always prior to the α-nucleated crystallization, as confirmed by crystalline morphology. These findings are useful for developing a new pathway to prepare iPP-based composite with good mechanical property via the addition of mixed nucleating system containing active inorganic filler and β-nucleating agent.     

Thermodynamic stability and retinol binding property of β-lactoglobulin in the presence of cationic surfactants

In this work the stability parameters of bovine β-lactoglobulin, variant A (BLG-A), with regard to their transition curves induced by dodecyltrimethylammonium bromide (C₁₂TAB), tetradecyltrimethylammonium bromide (C₁₄TAB) and hexadecyltrimethylammonium bromide (C₁₆TAB) as cationic surfactants, were determined at 298 K. For each transition curve, the conventional method of analysis which assumes a linear concentration dependence of the pre- and post-transition base lines, gave the most realistic values for ΔG_D(H₂O). The results represent the increase in the denaturating power of surfactants with an increase in hydrocarbon chain length. The value of about 22.27 kJ · mol^?1 was obtained for ΔG_D(H₂O) from transition curves. Subsequently, the retinol binding property of BLG as its functional indicator was investigated in the presence of these surfactants using the spectrofluorimeter titration method. The results represent the substantial enhancement of retinol binding affinity of BLG in the presence of these surfactants.     

Combined effect of modified zeolite 13X and β-nucleating agent on improving β-crystal content and toughening polypropylene random copolymer

Although addition of β-NUCLEATING agent directly into homo-polypropylene(PPH) is a useful method to improve β-CRYSTAL content and toughen PPH, polypropylene random copolymer(PPR) makes this method powerless due to its random structure and low crystallinity. In this study, the-nucleated PPR with high β-CRYSTAL content was prepared by a novel high effective β-NUCLEATING system which consists of-nucleation agent(TMB-5) and modified zeolite 13X(M13X). It was found that M13X and TMB-5 had a synergistic influence on improving β-CRYSTAL content and toughening PPR. The content of β-CRYSTAL in PPR/M13X/TMB-5 was significantly larger than the sum of that in PPR/M13X and PPR/TMB-5. Besides,fracture behavior, phase morphology and relaxation of matrix chain segments were also investigated. The results showed that M13X and TMB-5 improved the mobility of amorphous chain segments at low temperature and contributed to much energy dissipation. This work provides a powerful method to modify PPR.     

Mechanical properties and crystallization behavior of polypropylene with cyclodextrin derivative as ��-nucleating agent

It was found that lanthanum complex of cyclodextrin derivative (??-CD?CMAH?CLa) was a highly active ??-nucleating agent for isotactic polypropylene (iPP) in this study. The influence of the nucleating agent on mechanical properties and isothermal and nonisothermal crystallization behavior of iPP has been investigated. Results showed that ??-CD?CMAH?CLa was efficient in inducing the crystallization of iPP into ??-modification (??-iPP), with K _?? value of 0.84, while the content of nucleating agent was 0.8?wt.%. ??-iPP could form extensively in the isothermal crystallization temperature range from 110?°C to 140?°C, and the highest amount of ??-crystal content was formed at 130?°C. Besides, it can be known that the addition of ??-CD?CMAH?CLa can obviously facilitate the overall crystallization process of iPP. Under nonisothermal condition, ??-iPP formed at the suitable cooling rates, ranging from 5?°C to 10?°C/min. Furthermore, the nucleation mechanism of ??-CD?CMAH?CLa for iPP was correlated to the special configuration of ??-CD?CMAH?CLa.     

In situ synthesis of calcium pimelate as a highly dispersed β-nucleating agent for improving the crystallization behavior and mechanical properties of isotactic polypropylene

The reaction precursors pimelic acid (Pi) and calcium stearate (CaSt) were added in situ during extrusion of isotactic polypropylene (iPP) to generate self-dispersed calcium pimelate (CaPi[IS]). The results reveal that the nucleating agents (NAs) synthesized in situ obviously affected the nucleation effect in iPP. The crystallization, mechanical properties and melting behavior of nucleated iPP were investigated. The crystallization temperature (T_c) of iPP modified with CaPi(IS) increased by 4–5°C when compared to that of pure iPP. Especially, when the addition amount of CaPi(IS) in iPP was 0.30 wt%, the relative β-crystal concentration of iPP/CaPi(IS) reached the highest level of 96.47%, 22.71% higher than that of iPP/CaPi. However, Pi and CaSt has hardly impact on the nucleation effect in iPP. The mechanical properties of iPP show that CaPi and CaPi(IS) have excellent toughening effect on iPP while Pi and CaSt greatly improved the stiffness of iPP. Furthermore, the dispersion of these NAs in iPP was investigated by scanning electronic microscope (SEM). It can be clearly seen that the CaPi(IS) particles are uniformly distributed in the iPP after magnification.     

Study on side-chain liquid–crystalline copolymer as a new β-nucleating agent to induce phase behavior of isotactic polypropylene

The nucleating activity of side-chain liquid–crystalline copolymer, as new β-nucleating agent (LCP-NA3), towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. The effect of LCP-NA3 content, crystallization temperature, and time on the phase behavior of the iPP has been discussed. The results indicate that the relative content of β-crystal mainly depends on LCP-NA3 content, crystallization temperature, and time. A high content of β-crystal can be obtained by the combined effect of the optimum LCP-NA3 concentration, crystallization temperature, and time. The maximum content of β-crystal reaches 0.63 when the LCP-NA3 content, crystallization temperature, and time are 0.8 wt%, 130 °C, and 1 h, respectively. In addition, LCP-NA3 is identified to have dual nucleating ability for α- and β-crystals under appropriate kinetic conditions.     

Improved stability of organic field-effect transistor performance in oligothiophenes including β-isomers

Dialkyl quarter- and quinquethiophenes end-capped with β-connected thiophenes are prepared, and the field-effect transistor (FET) properties are investigated. Molecular orbital calculation as well as the redox and optical measurements indicate that the β-isomers have low-lying HOMO levels and large energy gaps compared with the α-isomers. Molecular packing of the dihexylquaterthiophene with β-isomers consists of a typical herringbone motif analogous to the α-isomers. In the single crystal, the alkyl chains are extending in the tilted directions from the core molecular plane, but straightly extending in the thin films, resulting in even more perpendicular molecular arrangement to the substrate than the α-isomers. These β-isomers show p-type FET performance comparable to the corresponding α-isomers, whereas all new oligothiophenes show air stability better than the corresponding α-isomers. In particular, dihexylquinquethiophene with β-isomers has shown significantly improved air stability maintained over 270 days. This stabilization effect is ascribed to the low-lying HOMO level and the dense packing realized by perpendicular molecular arrangement.