Synergistic enhancement of crystallization and mechanical performance of polypropylene random copolymer by strong shear and β‐nucleating agent

Investigation of microstructure and properties is critical for the development and application of polymer materials. Polypropylene random copolymer (PPR) and β‐nucleated PPR are widely used in water pipe production. The effect of melt shear flow on the crystalline structure and mechanical properties of PPR containing β‐nucleating agent needs in‐depth understanding. In this paper, we demonstrated the preparation of PPR and PPR containing 0.1 wt% calcium pimelate (Ca‐Pim) samples by conventional injection molding (CIM) and oscillation shear injection molding (OSIM). The multilayer structures and morphologies of the samples were characterized by SEM, two‐dimensional X‐ray scattering and DSC. The mechanical properties and the microstructures of samples prepared by these two injection molding methods were compared. Compared with samples prepared by CIM, the stronger shear provided by OSIM induced the formation of a thicker layer of a shish‐kebab structure and a higher content of γ crystals, and dramatically suppressed the β‐nucleating effect of Ca‐Pim. The OSIM samples have more shish‐kebab structures and higher crystallinities than CIM samples and therefore the former exhibit better rigidity than the latter. The β crystals in the core layer and the thicker layer of shish‐kebab structure endow OSIM‐PPR/0.1 wt% Ca‐Pim with excellent impact toughness. © 2017 Society of Chemical Industry     

Effects of rosin‐type nucleating agent on polypropylene crystallization

In this investigation the effects of a rosin‐type nucleating agent, which was prepared from cocrystallizing of dehydroabietic acid and Na‐dehydroabietate, on polypropylene (PP) crystallization were studied. The results of differential scanning calorimetry and X‐ray diffraction proved that a cocrystal of dehydroabietic acid and Na‐dehydroabietate was formed. The lower melting point of the cocrystal caused it to be uniformly dispersed in PP. When cocrystals were added as nucleating agent, the mechanical properties, heat distortion temperature, and crystallization temperatures of PP were obviously improved, and the size of spherulites was also decreased. This proved that the cocrystals of dehydroabietic acid and Na‐dehydroabietate could act as an effective nucleating agent for PP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1069–1073, 2002     

Interaction of self‐nucleation and the addition of a nucleating agent on the crystallization behavior of isotactic polypropylene

The relationship between heterogeneous or homogeneous nucleation and self‐nucleation of polypropylene (PP) and PP nucleated by an organic phosphate salt (PPA) was studied by DSC. For pure PP, it homogeneously nucleated during cooling after melting at the selected temperature (T_s) of 170–200°C for 3 min, but at the T_s of 160–168°C self‐nucleation occurred; PPA only nucleated heterogeneously at the T_s of 168–200°C, and there existed self nucleation at the T_s of 160–168°C. The double melting peaks of PP and PPA at the T_s of 162°C were observed. Once the self‐nucleation occurred, the change of the crystallization temperature and heat of fusion of PP is more significant than that of PPA with the change of the T_s, depending upon the crystallization conditions. Results were explained by homogeneous nucleation, heterogeneous nucleation, self‐nucleation, and annealing crystallization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 78–84, 2001     

Toughening effects of nucleating agent on impact polypropylene copolymer

In this study, the impact polypropylene copolymer (IPC) blended with the sorbitol‐based nucleating agent (NA) NX8000 was prepared and then characterized using a wide range of instrumentations. The results showed that the NA formed a fibril network which resulted in the increased viscosity of system and the decreased size of ethylene–propylene random copolymer (EPR) phase. The results of mechanical tests revealed “the brittle–ductile transition (BDT)” occurred while the ethylene content was between 3.5 wt % and 6 wt % and indicated that the impact strength of IPC was greatly improved by the addition of NX8000 when the EPR content was right over the critical value of BDT. The investigations provided valuable information for the further development of IPC materials and boarded its potential industrial applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40705.     

Effect of nucleating agent addition on crystallization of isotactic polypropylene

The isothermal and nonisothermal crystallization kinetics of nonnucleated and nucleated isotactic polypropylene (iPP) were investigated by DSC and a polarized light microscope with a hot stage. Dibenzylidene sorbitol (DBS) was used as a nucleating agent. It was found that the crystallization rate increased with the addition of DBS. The influence of DBS on fold surface energy, σ_e, was examined by the Hoffman and Lauritzen nucleation theory. It showed that σ_e decreased with the addition of DBS, suggesting that DBS is an effective nucleating agent for iPP. Ozawa's theory was used to study the nonisothermal crystallization. It was found that the crystallization temperature for the nucleated iPP was higher than that for nonnucleated iPP. The addition of DBS reduced the Ozawa exponent, suggesting a change in spherulite morphology. The cooling crystallization function has a negative exponent on the crystallization temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2089–2095, 1998     

Detecting crystallization structure evolution of polypropylene injection‐molded bar induced by nucleating agent

The crystallization structures of Polypropylene (PP) injection‐molded bars nucleated by nucleating agent were detected from the skin layer to the core zone, layer by layer. α‐phase nucleating agent 1,3:2,4‐bis (3,4‐dimethylbenzylidene) sorbitol (DMDBS, Millad 3988), β‐phase nucleating agent aryl amides compounds (TMB‐5), and their compounds were introduced into PP matrix, respectively. The relative content of β‐phase PP in the different zones of an injection‐molded bar was characterized and calculated by Wide angle X‐ray diffraction (WAXD) and Differential scanning calorimetry (DSC). The results show that, whether in pure PP or in nucleated PP, both β‐phase PP and α‐phase PP grow in the skin layer of the injection‐molded bar. However, in the intermediate layers and the core zone, the crystallization structures of PP are dependent on the used nucleating agent. β‐phase is the main crystallization structure of TMB‐5 (0.1 and 0.2 wt%) nucleated PP, and α‐phase in DMDBS (0.1 and 0.2 wt%) nucleated PP. Compounding nucleating agents with 0.1 wt% DMDBS and 0.1 wt% TMB‐5 induces PP crystallization almost in β‐phase; however, PP nucleated by 0.2 wt% DMDBS and 0.2 wt% TMB‐5 crystallizes exclusively in α‐phase. The crystallization mechanism of PP nucleated by compounding nucleating agents was further studied in this work. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Synergistic effects of β‐modification and impact polypropylene copolymer on brittle‐ductile transition of polypropylene random copolymer

In this work, the synergistic effects of β‐modification and impact polypropylene copolymer (IPC) on brittle–ductile (B–D) transition behavior of polypropylene random copolymer (PPR) have been investigated. It is interesting to find that adding both IPC and β‐nucleating agent into PPR has three effects: (i) leading to a significant enhancement in β‐crystallization capability of PPR, (ii) contributing to the shift of B–D transition to lower temperatures, (iii) increasing the B–D transition rate. The reason for these changes can be interpreted from the following two aspects. On one hand, the transition of crystalline structure from α‐form to β‐form reduces the plastic resistance of PPR matrix, thus causing the initiation of matrix shear yielding much easier during the impact process. On the other hand, the well dispersed rubbery phase in IPC with high molecular mobility at relatively low temperatures is beneficial to the shear yielding of PPR matrix and, subsequently, the great improvement in impact toughness of the ternary blends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of rosin‐type nucleating agent and low density polyethylene on the crystallization process of polypropylene

In this article, the influence of rosin‐type nucleating agent (Nu–Na) and low density polyethylene (LDPE) on the crystallization process of polypropylene (PP) from the melt state was studied by differential scanning calorimeter and polarization microscope. It was found that LDPE obstructed the crystallization of PP, decreased the crystallization rate of PP. The rosin‐type nucleating agent Nu–Na substantially improved the rate of crystallization, and decreased the size of spherulites also. The cooperative effect of LDPE and Nu–Na made the crystallization rate of PP increase greatly, the spherulites of PP became much smaller and dispersed more uniformly, and the transparency of PP was further improved evidently. The crystallization temperature (T_c) and melting temperature (T_m) of PP and LDPE in PP/LDPE/Nu–Na (97:3:0.5) were not affected by the number of mixed passes—the nuclei migration from PP to PE had not happened in the mixed passes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2804–2809, 2003     

成核剂对聚丙烯力学性能与结晶行为的影响

研究了两种类型的成核剂对国产共聚聚丙烯的结晶形态以及拉伸强度、冲击强度的影响。结果表明:加入TMB-5型成核剂,聚丙烯的冲击强度有一定程度改善,w(TMB-5)为0.1%时,改性聚丙烯的缺口冲击强度达到最大;TMX-2型成核剂可改善聚丙烯的拉伸性能,但抗冲击性能降低较大;TMB-5型成核剂可显著地改变聚丙烯的结晶行为,诱导聚丙烯在结晶过程中主要形成β晶;TMX-2型成核剂可诱导聚丙烯在结晶过程中主要生成α晶,与纯PP相比,α晶的形成能力增强。     

Controllable reinforcement of stiffness and toughness of polypropylene via thermally induced self‐assembly of β‐nucleating agent

An easy approach was reported to achieve the simultaneous reinforcement and toughening of polypropylene (PP) via thermally induced self‐assembly of β‐nucleating agent (TMB‐5). The results showed that the processing temperatures dictated the solubility and self‐assembly of TMB‐5 in the polymer melts to determine the subsequent morphology development of PP. At low processing temperature, TMB‐5 did not dissolve into the polymer melt but remained original shape to induce PP to crystallize into spherulites so that it only promoted the formation of β‐form crystals to enhance the toughness of the samples. At high processing temperature, TMB‐5 gradually dissolved into the polymer melts. On cooling, the dissolved nucleating agent self‐assembled into high aspect ratio fibrils through intermolecular hydrogen‐bonding interactions. Due to a favorable matching between PP and TMB‐5, PP preferred to nucleate and grow orthogonally to the fibril axis and into oriented hybrid shish‐kebab morphology with rich β‐form crystals. Compared with isotropic spherulites, the anisotropic structure exhibited excellent properties of the β‐form crystal and shish‐kebab morphology to simultaneously improve the strength and toughness of TMB‐5‐modified PP samples. With the increasing processing temperature, more dissolved TMB‐5 was involved in the self‐assembly procedure to generate longer fibrils and induce more lamellae to grow on the surface. As a consequence, the anisotropy of the PP samples increased further, bringing out more improvements of the tensile strength. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40605.     

Combined effect of β‐nucleating agent and processing melt temperature on the toughness of impact polypropylene copolymer

The phase morphology and toughening behavior of impact polypropylene copolymer (IPC) with and without nucleating agent (NA), prepared at different processing melt temperatures (T_p), were investigated. Interestingly, three different structures can be formed in the IPC samples by adding NA or tuning T_p. A well‐defined core–shell structure is obtained in samples with α‐NA or without NA prepared at all T_p. A developing multilayered structure is mainly formed at high T_p with added β‐NA, while an incomplete phase separation structure with interpenetrating chains is the dominant structure for IPC samples prepared at low T_p with added β‐NA. In this case, because of the synergistic effect between phase morphology and relatively high β‐form crystal content, the chain interaction among the components and chain mobility of the amorphous portion of IPC are distinctly improved, resulting in a largely improved toughness under 0 °C. This improvement in toughness is very important for applications. © 2012 Society of Chemical Industry     

A highly efficient β‐nucleating agent for impact‐resistant polypropylene copolymer

In this work, we reported calcium tetrahydrophthalate as a high efficient β‐nucleating agent (β‐NA) for impact‐resistant polypropylene copolymer (IPC). The relative fraction of the β‐crystal can reach as high as 93.5% when only 0.03% β‐NA is added. The non‐isothermal and isothermal crystallization behaviors, morphology, lamellar structure and mechanical properties of IPCs with various β‐NA contents were studied. During non‐isothermal crystallization, the cooling rate has an important influence on the relative fraction of the β‐crystal, which decreases remarkably as the cooling rate increases. The β‐NA also greatly accelerates crystallization rate of IPC, resulting from both more crystal nuclei and larger Avrami exponent. The small angle X‐ray scattering characterization shows that more amorphous components are included into the inter‐lamellae after addition of β‐NA. Dynamical mechanical analysis (DMA) reveals that the storage modulus at low temperature and the loss factor above 0 °C from the PP component can be enhanced upon addition of β‐NA and reach a maximum at the β‐NA content of 0.05 wt %. Impact test shows that the impact strength of the IPC at 0°C can be improved as much as 40% when the content of calcium tetrahydrophthalate is 0.10 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40753.     

Influence of a sorbitol‐based nucleating agent modified with silsesquioxanes on the non‐isothermal crystallization of isotactic polypropylene

This article investigates the effect of modifying the polypropylene (iPP) α‐phase nucleating agent 1,3:2,4‐bis(3,4‐dimethylbenzylidene) sorbitol (DMDBS) with tetrasilanolphenyl silsesquioxane (phPOSS). It has been proven that an increasing amount of silsesquioxane leads to differences in the crystallization behavior. What is more, it has been observed that the nucleation effect that results from the addition of sorbitol derivatives is suppressed by phPOSS activity. To understand the influence of phPOSS addition on the crystallization kinetics of PP/DMDBS/phPOSS composites that have been prepared by melt processing in a twin screw extruder, differential scanning calorimetry, rotational rheometry and Fourier transform infrared spectroscopy are performed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40131.     

Influence of a particulate nucleating agent on the quiescent and flow-induced crystallization of isotactic polypropylene

Flow induced crystallization of commercial isotactic polypropylene (iPP) and its blends with sodium 2,2′-methylene bis-(4,6-di-tert-butylphenyl) phosphate (also known as NA11) is studied by means of in-situ time resolved small-angle X-ray scattering (SAXS). The isothermal crystallization at 145 °C (i.e. well below melting temperature of polymer) is performed after the application of steady shear to probe the anisotropic structure formation. In order to separate the influence of shear rate and shear time on polymer crystallization, four different shear conditions (60 s⁻¹ for 1 s, 30 s⁻¹ for 2 s, 15 s⁻¹ for 4 s and 6 s⁻¹ for 10 s) are applied while maintaining the same imposed strain in the polymer melt. Further the effect of different concentration of nucleating agent on the crystallization kinetics of iPP is examined both under quiescent and shear flow conditions. For instance, under quiescent condition, the crystallization half-time (τ_1/2) decreases with the increasing concentration of nucleating agent in the polymer. Under shear flow conditions, our observations are as follows: In the case of neat iPP, τ_1/2 decreases significantly at higher shear rates (≥30 s⁻¹). Compared to the neat iPP, for the same concentration of NA11 in the NA11/iPP blends differences in τ_1/2 with the increase in applied shear rates are significantly smaller. In other words, the crystallization kinetics is dominated by the amount of nucleating agent in the NA11/iPP blends as opposed to shear rates in the neat iPP. The present study shows that the critical value of shear rate required for chain orientation in the molten polymer is lower in the presence of the nucleating agent compared to neat iPP. The self-nucleation process investigated with the aid of differential scanning calorimetry (DSC), indicates that the nucleating efficiency of NA11 on iPP is around 60%.     

成核剂对聚丙烯性能的影响

研究了各种α晶型成核剂和β晶型成核剂对聚丙烯性能的影响,发现用α晶型成核剂NA-11和用N催化剂生产的高等规指数聚丙烯组合,可制成透明型高强度、高耐热聚丙烯。这种高性能聚丙烯在家电、汽车等方面具有极为广泛的应用前景。     

Synergistic effects of α/β‐nucleating agents on propylene‐ethylene random copolymer: New clues for the pipe extrusion

Adding β‐nucleating agents (β‐NAs) has been generally considered as an effective approach to induce the formation of β‐crystals in propylene‐ethylene random copolymer (PPR). However, it is still difficult to obtain the expected percentage of β‐crystal under normal processing conditions, due to the temperature control is always a key factor no matter with or without adding β‐NAs. We assumed that simultaneously adding both α‐ and β‐NAs to PPR in rational ratios would facilitate the growth of β‐crystal. The effects of adding various amount of α‐ and/or β‐NAs on the α‐ and β‐crystallization behavior and morphology were investigated. More importantly, the influence of temperature control on inducing β‐crystal in the presence of different NAs was parallel explored by utilizing sample bars prepared via injection molding and sample pipes produced from a typical industrial extrusion line. Different crystallization situations were carefully discussed in response to various nonisothermal crystallization processes in laboratory experiments and in actual pipes extrusion. At last, the mechanical properties of PPR samples were examined to provide new clues for further study of PPR pipes. POLYM. ENG. SCI., 56:1089–1095, 2016. © 2016 Society of Plastics Engineers     

The effect of a sodium octacosanoate‐based nucleating agent on the crystallization of thermoplastic polyurethanes

Sodium octacosanoate (NaC_28‐32) is commonly used as a nucleating agent in polyester and polyamide formulations. In this work, the effect of adding this agent to three chemically identical thermoplastic polyurethanes (TPUs), but with distinct molecular weights, was addressed, focusing on the study of the crystallization phenomenon. The modified Avrami and Avrami‐Ozawa kinetic models were applied to the isothermal and non‐isothermal crystallization processes, respectively, and both indicated faster crystallization when the nucleating agent was used, with an increase in temperature and rate of crystallization of the TPU. Such effect was partly attributed to the formation of a larger number of crystallization nuclei in comparison to the neat TPU. Besides, the nucleating effect was more pronounced for the TPU with the lowest molecular weight (30,000 Dalton). The Avrami and Avrami‐Ozawa models indicated that the TPU crystallization process occurs with the development of two‐dimensional lamellar aggregates, axialites, and that the incorporation of thenucleating agent does not alter this geometry. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene and elastomer blends

The influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene (iPP), in their blends with poly(styrene-b-ethylene butylene-b-styrene) (SEBS), and a metallocenic ethylene-octene copolymer (EO) was investigated by DSC, optical microscopy and real-time small and wide angle X-ray scattering (SAXS and WAXS) experiments using synchrotron radiation. In non-nucleated iPP/SEBS blends, the crystallization of the iPP matrix occurred in the presence of the styrenic domains which induced a nucleating effect on the process, as observed in the synchrotron experiments. The metallocenic elastomer did not affect the crystallization behaviour of iPP in the iPP/EO blends in non-isothermal experiments, however, the development of crystallinity in the elastomer was restricted. In the nucleated isotactic polypropylene/elastomer blends a significant increase in the crystallinity and the crystallization rate of the iPP matrix was observed due to the presence of the nucleating agent. However, the nucleating efficiency of the additive was strongly affected by the nature and content of the elastomeric component. The nucleating agent efficiency was higher in the presence of the ethylene-octene component than the styrenic elastomer.     

Dynamic mechanical properties,crystallization behaviors,and low‐temperature performance of polypropylene random copolymer composites

In this study, polypropylene random copolymer (PPR) composites were prepared by the addition of either three kinds of thermoplastic rubber (TPR) modifiers (types 2088A, 2095, and 2096) or an ethylene–octene copolymer (POE)/high‐density polyethylene (HDPE; 2 :1 w/w) blend. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and dynamic mechanical analysis were used to characterize the crystallization behaviors and dynamic mechanical properties of the PPR composites. The results indicated that PPR/POE/HDPE and PPR/TPR2088A had better comprehensive mechanical properties, especially the low‐temperature toughness among all of the samples. The obtained PPR/POE/HDPE blends showed a high toughness and good stiffness in the temperature interval from ?10 to 23°C with the addition of only 10 wt % POE/HDPE. When the temperature continued to fall below ?10°C, the PPR/TPR2088A composites exhibited a better impact toughness without a loss of too much stiffness. The good low‐temperature toughness of those two composites was attributed to both the decrease in the crystallinity and the uniform dispersion, obvious interfacial adhesion, and cavitation ability of POE/HDPE and TPR2088A in the PPR matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42960.     

Variation of non‐isothermal crystallization behavior of isotactic polypropylene with varying β‐nucleating agent content

The non‐isothermal crystallization behavior, the crystallization kinetics, the crystallization activation energy and the morphology of isotactic polypropylene (iPP) with varying content of β‐nucleating agent were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The DSC results showed that the Avrami equation modified by Jeziorny and a method developed by Mo and co‐workers could be successfully used to describe the non‐isothermal crystallization process of the nucleated iPPs. The values of n showed that the non‐isothermal crystallization of α‐ and β‐nucleated iPPs corresponded to a tridimensional growth with homogeneous and heterogeneous nucleation, respectively. The values of crystallization rate constant showed that the rate of crystallization decreased for iPPs with the addition of β‐nucleating agent. The crystallization activation energy increased with a small amount (less than 0.1 wt%) of β‐nucleating agent and decreased with higher concentration (more than 0.1 wt%). The changes of crystallization rate, crystallization time and crystallization activation energy of iPPs with varying contents of β‐nucleating agent were mainly determined by the ratio of the content of α‐ and β‐phase in iPP (α‐PP and β‐PP) from the DSC investigation, and the large size and many intercrossing lamellae between boundaries of β‐spherulites for iPPs with small amounts of β‐nucleating agent and the small size and few intercrossing bands among the boundaries of β‐spherulites for iPPs with large amounts of β‐nucleating agent from the SEM examination. Copyright © 2010 Society of Chemical Industry