Polypropylene Random Copolymer Research Articles

Stepwise crystallization method combining isotactic polypropylene-based plastic waste film to prepare high-performance polypropylene random copolymer

Upcycling of waste plastic film is increasingly important at the background of energy shortage and environmental crisis. However, direct reuse of the waste plastics as reworked material inevitably downgrades the mechanical properties. Herein, a stepwise crystallization method was combined to enable the recycling of waste isotactic polypropylene (iPP) film value-added in iPP-based homocomposites. In detail, the effect of β-nucleating agent (β-NA) and iPP on crystallization behaviors of polypropylene random copolymer (PPR) was investigated at first. The stepwise crystallization procedure was further introduced to promote the β-crystallization of PPR/iPP/β-NA composites in which the crystal structures, polymorph compositions and phase morphologies were systematically researched. At last, impact behaviors of PPR/iPP/β-NA composites were characterized and a penitential toughening mechanism was proposed. It was found that the stepwise crystallization boosted β-crystallization and growth of rubbery phase during the isothermal procedure, resulting an increase of relative β-crystal content and low temperature impact toughness from 0% and 2.02 kJ/m2 of neat PPR to 33.4% and 3.06 kJ/m2 of PPR/iPP/β-NA composites. This work provides a simple, implementable, and effective method for the recycling of waste iPP films and the low-temperature toughening of PPR.

Toughening mechanism of α/β core-shell structure for high toughness polypropylene random copolymer

Weak interfaces can impede crack propagation in rigid natural materials containing small amounts of organic compounds. Inspired from this, we start from the core-shell structured isotactic propylene (iPP)/polypropylene random copolymers (PPR) homocomposites and construct serval kinds of interfaces to study the toughening mechanisms by applying the crystallization epitaxies of PPR on iPP. Through molecular chain diffusion and crystallization epitaxy, derived models from microscopic core-shell structured crystals in the homocomposites to macroscopic layer-by-layer assemblies with different interfaces are established to magnify the role that each layer plays during crack initiation and propagation. As a result, the ductile β-PP interface can decrease crack tip strength so that a further step of crack initiation is triggered in the composite laminates with a fold of fracture energy consumption compared to the laminates with weak or rigid interfaces. At last, we come back to the core-shell structured homocomposites and toughen them with an improve in impact toughness from ∼10.8 to ∼18.2 kJ/m2 by manipulating the content of ductile interfaces. This work provides a novel research routine and a new toughening mechanism toward the toughening of PP and can be extended to study the fracture mechanisms of other toughening systems with core-shell structures.

The Crystallization Morphology and Conformational Changes of Polypropylene Random Copolymer Induced by a Novel β-Nucleating Agent.

The crystal morphology and conformational changes during crystallization of a polypropylene random copolymer (PPR) are the basis for understanding its crystallization process. In this work, novel rare-earth β-nucleating agent WBN-28 was directly added into PPR to induce β-crystallization. The results of differential scanning calorimetry (DSC) showed that it has an excellent β-crystal-induced effect. The β-crystal content could surpass 85%, calculated from wide-angle X-ray diffraction (WAXD) data. The morphology of the β-crystal and α-crystal was intuitively observed via a polarizing optical microscope (POM). The β-crystallites were interconnected to naturally develop plate-like crystalline regions possessing a certain size, and the α-crystallites with sufficient thicknesses possessed a cross-hatched phenomenon. The bundle-like supramolecular structure of the β-crystal induced by WBN-28 was further observed via a scanning electron microscope (SEM). The conformational changes in the crystallization process of PPR were resolved via high-resolution infrared spectroscopy to understand its β-crystallization in depth. The conformational changes during the crystallization of PPR were found to be different from those of the isotactic polypropylene homopolymer (PPH); they had their own characteristics. This will provide guidance for understanding the β-crystallization of PPR in depth.

Design and analysis of serviceable cantilever fit snap in automotive plastic parts

Purpose Snap fits are crucial in automotive applications for rapid assembly and disassembly of mating components, eliminating the need for fasteners. This study aims to focus on designing and analyzing serviceable cantilever fit snap connections used in automobile plastic components. Snap fits are classified into permanent and semi-permanent fittings, with permanent fittings having a snap clipping angle between 0° and 5° and semi-permanent fittings having a clipping angle between 15° and 45°. Polypropylene random copolymer is chosen for its exceptional fatigue resistance and elasticity. Design/methodology/approach The design process includes determining dimensions, computing assembly, disassembly pressures and creating three-dimensional computer-aided design models. Finite element analysis (FEA) is used to evaluate the snap-fit mechanism’s stress, deformation and general functionality in operational scenarios. Findings The study develops a modified snap-fit mechanism with decreased bending stress and enhanced mating force optimization. The maximum bending stress during assembly is 16.80 MPa, requiring a mating force of 7.58 N, while during disassembly, it is 37.3 MPa, requiring a mating force of 16.85 N. The optimized parameters significantly improve the performance and dependability of the snap-fit mechanism. The results emphasize the need of taking into account both the assembly and disassembly processes in snap-fit design, because the research demonstrates greater forces during disassembly. The approach developed integrates FEA and design for assembly (DFA) concepts to provide a solution for improving the efficiency and reliability of snap-fit connectors in automotive applications. Originality/value The research paper’s distinctiveness comes from the fact that it presents a thorough and realistic viewpoint on snap-fit design, emphasizes material selection, incorporates DFA principles and emphasizes the specific requirements of both assembly and disassembly operations. These discoveries may enhance the efficiency, reliability and sustainability of snap-fit connections in plastic automobile parts and beyond. In conclusion, the idea that disassembly needs to be done with a lot more force than installation in a snap-fit design can have a good effect on buzz, squeak and rattle and noise, vibration and harshness characteristics in automobiles.

Effect of silver particles on the crystal structure and the mechanical, optical and antibacterial properties of various polypropylene based plastomers and elastomers

In composite materials consisting of silver particles and a polypropylene matrix, the silver must migrate to the surface of the materials in order to exert on antibacterial effect. Substrates with various crystal structures may have different interactions with the silver particles, which can significantly impact the antibacterial performance. The research described in this paper investigates the influence of silver particles on the crystallization behavior of materials with varying crystallinity capabilities by selecting various polypropylene-based plastics and elastomers (Homopolymer polypropylene (PPH-T03), random poly(propylene/ethylene) copolymers (PPR-YPR503 and PPR-P340R), polyolefin elastomers (VERSIFY3000 (POE-1) and VERSIFY3401 (POE-2)), and ethylene propylene diene monomer for polymers (EPDM4725 and EPDM4770)). The research results indicated that the silver only entered the amorphous regions of the PP rather than entering the crystal regions, where they can more easily migrate to the material surface, resulting in a higher antibacterial effect. Therefore, the antibacterial degree of PP-Ag was as high as 99.9%. Silver can enter the micro-crystals of both the random copolymer polypropylene, (PPR-YPR503, PPR-1) and the random copolymer polypropylene, (PPR-P340R, PPR-2,) with a stronger effect on PPR-2. More silver entered the micro-crystals of PPR-2, and it was difficult for the silver ions to migrate out of the crystalline regions to exhibit antibacterial properties. The antibacterial degree of PPR-1-Ag was higher than that of PPR-2-Ag (77.8% vs. 66.7%). Similarly, silver had a greater impact on the lamellar structure of the polyolefin elastomer (VERSIFY3401, POE-2) compared to the polyolefin elastomer (VERSIFY3000, POE-1). In comparison with POE-2-Ag, POE-1-Ag exhibited a higher antibacterial degree (79.6% vs. 57.4%). Research on the two types of ethylene propylene diene monomer (EPDM) composite materials indicated that EPDM-1 exhibited a lower Mooney viscosity and poorer flowability. The EPDM-1 tended to encapsulate the silver within its molecular chains, thereby impeding the migration of silver to the surface. The optical performance analysis indicated that silver antibacterial agents had little impact on the optical properties of PP-Ag, PPR-1, PPR-2, POE-1, POE-2 and the EPDMs. We suggest that this research provides theoretical guidance for selecting highly antibacterial polypropylene materials.

An efficient β-nucleating agent with high lattice matching rate for plate-like crystallization of polypropylene random copolymer.

It is challenging to naturally produce large amounts of β-crystals by directly adding a commercial β-nucleating agent (β-NA) into polypropylene random copolymer (PPR) at present. In this work, a novel rare earth β-NA WBN-28 was directly introduced into PPR to prepare β-PPR with high β-crystal conversion. The results of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) indicated that it is an efficient β-NA for PPR. The β-conversion rate (β-CR) could surpass 85% when the nucleating agent content was mere 0.05%. With the further increment of nucleating agent, the β-CR increased gradually, which could reach 89.5% and 86.9% respectively calculated by DSC and WAXD when the addition amount was 0.4%. The incredible high β-CR delayed the βα-recrystallization in isothermal crystallization. The fusion peak of α-crystal was unobserved below the isothermal crystallization temperature of 122 °C when the addition amount was more than 0.2%. Furthermore, there was a highly ordered structure in WBN-28 with the periodicity of 12.89 Å, which was approximately twice of the unit cell parameter in the c direction of β-PP, indicating a high lattice matching rate between them. Intuitively observed by polarizing optical microscope (POM), the crystal grains of the blends with β-NA were more refined and finally crystallized in a plate-like shape. The forming process of the plate-like β crystalline regions were proposed by scanning electron microscope (SEM) and POM.

Exploitation of a New Nucleating Agent by Molecular Structure Modification of Aryl Phosphate and Its Effect on Application Properties of the Polypropylene.

In this work, a novel α-nucleating agent (NA) for polypropylene (PP) termed APAl-3C-12Li was prepared and evaluated compared with the commercially available type NA-21. For the synthesis of the organophosphate-type NA (APAl-3C), the -OH group of the acid part of NA-21 was substituted by the isopropoxy group. The structure of APAl-3C was analyzed by spectroscopy and element analysis, the results of which were consistent with the theoretical molecular formula. APAl-3C's thermal stability was studied by differential scanning calorimetry (DSC) and thermogravimetry (TG), which showed only weak mass loss below 230 °C, meaning that it would not decompose during the processing of PP. The APAl-3C-12Li was used as a novel nucleating agent, studying its effects on crystallization, microstructure, mechanical and optical properties. Tests were performed in a PP random copolymer at different contents, in comparison to the commercial NA-21. The composite with 0.5 wt% APAl-3C-12Li has a similar crystallization temperature of 118.8 °C as with the addition of 0.5 wt% NA-21. An advantage is that the composite with the APAl-3C-12Li has a lower haze value of 9.3% than the counterpart with NA-21. This is due to the weaker polarity of APAl-3C-12Li after the introduction of methyl and better uniform dispersion in the PP matrix, resulting in stronger improvement of optical and mechanical properties.

Investigation of tribo-mechanical performance of alkali treated rice-husk and polypropylene-random-copolymer based biocomposites

This study was based on the experimental performance evaluation of a wood polymer composite (WPC) that was synthesized by incorporating untreated and treated rice husk (RH) fibers into a polypropylene random copolymer matrix. The submicron-scale RH fibers were alkali-treated to modify the surface and introduce new functional groups in the WPC. A compatibilizer (maleic anhydride) and a thermos-mechanical properties modifier (polypropylene grafted with 30 % glass fiber) were used in the WPC. The effects of untreated and treated RH on the WPC panels were studied using FESEM, FTIR, and microscope images. A pin-on-disk setup was used to investigate the bulk tribological properties of PPRC and WPC. The complex relationship between the friction coefficient of different loading of RH fibers in the WPC, as a function of sliding distance, was analyzed along with the temperature and morphology of the surface. It was observed that untreated RH acted as a friction modifier, while treated RH acted as a solid lubricant. Microhardness was calculated using the QCSM module on nanoindentation. It was found that untreated RH led to an increase in microhardness, while treated RH caused a decrease in hardness compared to PPRC.

Effect of hydrophobic nano‐silica/β‐nucleating agent on the crystallization behavior and mechanical properties of polypropylene random copolymers

AbstractIn this work, hydrophobic nano‐silica (SiO2) and β‐nucleating agent are incorporated into polypropylene random copolymer (PP‐R) matrix by melt blending. The effect of the content of nano‐SiO2/β‐nucleating agent on the crystallization and mechanical behaviors of PP‐R was investigated in detail. For a nano‐SiO2 content of 0.5 wt% and a β‐nucleating agent content of 0.5 wt%, the tensile strength and impact strength of the composite were in a more balanced position. Regarding isothermal and non‐isothermal crystallization experiments, nano‐SiO2/β‐nucleating agent significantly accelerated the nucleation and growth of crystallites with a synergistic nucleation effect. Also, the crystallization kinetics of PP‐R/nano‐SiO2/β‐nucleating agent, PP‐R/nano‐SiO2 and PP‐R/β‐nucleating agent composites were analyzed and compared using the Avrami equation. The results showed that the PP‐R/nano‐SiO2/β‐nucleating agent composites have better crystallization rate and shorter semi‐crystallization time. This study shows far‐reaching theoretical and practical implications for accelerating the development of new high‐performance PP‐R materials. © 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Toward a Further Understanding of the Decreased β-Phase Content in β-Nucleated Polypropylene Random Copolymer: From Nucleation and Growth Kinetics

Toward a Further Understanding of the Decreased β-Phase Content in β-Nucleated Polypropylene Random Copolymer: From Nucleation and Growth Kinetics

Factors affecting the leaching of micro and nanoplastics in the water distribution system

The role of the water distribution system (WDS) requires that it supply water of sufficient quality to households. Unregulated leaching of micro and nanoplastics from plastic pipes of the distribution system is therefore a cause for concern, particularly with the rise in research associating these plastic particles to adverse health impacts in living organisms. Within this study, four parameters (pH, free chlorine concentration, pipe material, and time) were varied in a pipe loop network to observe their effect on microplastic (MP) and nanoplastic (NP) leaching into the simulated distribution network. Results indicated an abundance of MPs/NPs in different shapes and sizes throughout the samples. Graphical trends illustrated that basic pH values contributed to a higher number of particles. Statistical analysis via analysis of variance (ANOVA) confirmed this observation and further showed interaction of chlorine dose and pH concentration (p-value = 0.000), and chlorine dose and pipe material (p-value = 0.038) was also significant to leaching. Numerically, polyethylene (PE) particles were the most abundant with a total of 15194 particles, followed by 12920 polypropylene random copolymer (PPR) particles and 12317 polyvinyl chloride (PVC) particles. It was also noticed that the number of particles decreased with time.© 2023 Elsevier Inc. All rights reserved.

How 4-(7-Octen-1-yl)-N,N-diphenylaniline co-units induce strong melt memory effects in isotactic polypropylene random copolymers

The random incorporation of comonomer units in isotactic polypropylene usually disrupts the chemical regularity of the macromolecular chain, thereby remarkably affecting the crystallization and melting processes. We study the influence of a novel comonomer 4-(7-Octen-1-yl)-N,N-diphenylaniline (ODPA), in the concentration range of 1.1–6.8 mol%, on the crystallization and self-nucleation behavior of isotactic polypropylene copolymers. Non-isothermal and isothermal differential scanning calorimetry experiments demonstrated that crystallization kinetics are significantly retarded upon comonomer incorporation as the ODPA co-units are excluded to the amorphous regions. Furthermore, ODPA comonomer incorporation leads to a sharp increase in nucleation density; thus, spherulitic superstructures become significantly smaller. Remarkably, the ODPA co-units induce a strong melt memory effect that can persist even above the equilibrium melting temperature for copolymers with 4.4–6.8 mol% ODPA. The width of Domain IIa (exclusive melt-memory domain), an indicator of the self-nucleation strength, starts to increase sharply once the content of ODPA exceeds 1.8 mol%. In contrast, the width of Domain IIb (self-seeding domain) remains constant. We attribute the self-nucleation effect in these ODPA copolymers to the aggregation of co-units in the interlamellar amorphous regions that hinder, upon melting, the motion of the chain sequences that were initially packed within the crystal lattice. In this way, to reach the isotropic melt state, the sample must be heated to much higher temperatures than its apparent or even equilibrium melting point, depending on the comonomer content. Consequently, nucleation upon cooling from the self-nucleated melt becomes easier and faster.

Step crystal growth on β-nucleated polypropylene homocomposites governing the crystalline compositions

Polymorphisms of polypropylene random copolymers (PPR) are usually regulated by the amplified β-nucleating effect of isotactic polypropylene (iPP). Nevertheless, the synergetic effect of β-nucleating agents (β-NAs) and iPP on growth of β-PPR crystals are still unclear to explain the debated content of β crystals obtained in the literatures. In this work, the growth mechanisms of PPR on β-nucleated iPP and the benchmarks were systematically revealed and discussed. First, a crystalline order is found existed in the PPR/iPP/β-NA ternary composite system. Then, the step crystal growth of each component is confirmed by the stepwise isothermal crystallization via microscopes. The results show that β-PPR crystallizes on the front of pre-crystallized β-iPP and is terminated by the adjacent α-PPR crystals. The overgrowth and spatial contact restrictions lay down a nucleation-controlled procedure. The morphologies and polymorph compositions can be regulated on the relative sizes of core and shell crystals, which are then determined by the size of β-iPP pre-crystallites, β-NA concentrations and the final heating temperature (Tf). At last, a high Kβ up to 0.5 can be easily reproduced at a low filling concentration of 0.3% β-NAs based on the nucleation-controlled β-growth. The easy preparation strategy of β-PPR that allows diversified thermal processing of PPR/iPP/β-NA composites enriches the researches on structure–performance relationship via macromolecular engineering.

Coupled thermal stress and moisture absorption in modified a montmorillonite/copolymer nanocomposite: Experimental study

N-Dimethylhexadecyclamine (DMHDA+) montmorillonite (Mt) random copolymer polypropylene (CPP-R) nanocomposites (AmK10CPP-R) are increasingly used in industrial applications such as coating subsea pipelines because they have excellent thermomechanical and barrier properties in front of two coupled properties of moisture adsorption and thermal loading. The coupled properties are experimentally investigated at temperature levels of 298 K and 370 K and water content of 0.0% wt. and 100% wt at 1.0 atm. for three different weight fractions (wt. %) of 0.3%, 3%, and 4% of the nanoparticles. X-Ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), static tensile tests, and dynamic material tensile analysis (DMTA) are conducted on the test samples. XRD pattern of nanofiller shows that using loading content less than 1% wt cannot provide a good basal spacing of nano fillers. The nanocomposite sample with major quantity of clay (4%AmK10CPP-R) presented less clusters of clay dispersed by FE-SEM. DSC indicates that glass transition temperature of 3% AmK10CPP-R is the highest value among all samples and melting temperature of all samples does not change. Moreover, it is observed that the diffusion coefficient of the saturated 4% wt. modified clay random copolymer (4AmAMoisK10CPP-R) is decreased almost 79.4% in comparison with 0.3AmMoisK10CPP-R sample at ambient temperature and atmospheric pressure. Furthermore, thermal analysis shows that temperature and loss of the mass at first stage are the lowest values for 4%AmMoisK10CPP-R. However, thermal stability of the saturated sample is increased in the second stage of TGA/DTG. It is seen that the clay nanoparticle can significantly hinder the degradation of mechanical properties of the nanocomposite even when both temperature and water content increase. Stress-strain curve gives that 3% and 4% wt. modified clay in the polymer matrix can significantly increase the mechanical properties of the polymer. Finally, DMTA determines that the 3%AmAMoisK10CPP-R gives the highest elastic modules. This study finds that mechanical, thermal and rheological properties of the polymer nanocomposite improve and the best compatibilising effect is at a content 3 wt% of the modified clay.

Multifunctional characteristics of 3D printed polymer nanocomposites under monotonic and cyclic compression

This study presents the multifunctional characteristics of multi-walled carbon nanotube (MWCNT)/polypropylene random copolymer (PPR) composites enabled via fused filament fabrication (FFF) under monotonic and quasi-static cyclic compression. Utilizing in-house MWCNT-engineered PPR filament feedstocks, both bulk and cellular composites were realized. The morphological features of nanocomposites were examined via scanning electron microscopy, which reveals that MWCNTs are uniformly dispersed. The uniformly dispersed MWCNTs forms an electrically conductive network within the PPR matrix, and the resulting nanocomposite shows good electrical conductivity (⁓10−1S/cm), improved mechanical performance (modulus increases by 125% and compressive strength increases by 25% for 8 wt% MWCNT loading) and pronounced piezoresistive response (gauge factor of 27.9–8.5 for bulk samples) under compression. The influence of strain rate on the piezoresistive response of bulk samples (4 wt% of MWCNT) under compression was also measured. Under repeated cyclic compression (2% constant strain amplitude), the nanocomposite exhibited stable piezoresistive performance up to 100 cycles. The piezoresistive response under repeated cyclic loading with increasing strain amplitude of was also assessed. The gauge factor of BCC and FCC cellular composites (4 wt% of MWCNT) with a relative density of 30% was observed to be 46.4 and 30.2 respectively, under compression. The higher sensitivity of the BCC plate-lattice could be attributed to its higher degree of stretching-dominated deformation behavior than the FCC plate-lattice, which exhibits bending-dominated behavior. The 3D printed cellular PPR/MWCNT composites structures were found to show excellent piezoresistive self-sensing characteristics and open new avenues for in situ structural health monitoring in various applications.

The disinfectant residues promote the leaching of water contaminants from plastic pipe particles

Disinfection treatment is an indispensable water purification process, but it can leave trace concentrations of disinfectant in the purified water. Disinfectants oxidation can age plastic pipes and release hazardous microplastics and chemicals into drinking water. Lengths of commercially-available unplasticized polyvinyl chloride and polypropylene random copolymer water pipe were ground into particles and exposed to micro-molar concentrations of ClO2, NaClO, trichloroisocyanuric acid, or O3 for up to 75 days. The disinfectants aged the plastic and changed its surface morphology and functional groups. Meanwhile, disinfectants could significantly promote the release of organic matter from plastic pipes into the water. ClO2 generated the highest concentrations of organic matter in the leachates from both plastics. Plasticizers, antioxidants and low molecular weight organic matter were detected in all of the leachates. Leachate samples inhibited the proliferation of CT26 mouse colon cancer and induced oxidative stress in the cells. Even trace concentrations of residual disinfectant can constitute a drinking water risk.

Reactive Extrusion of Multifunctional Conducting Nanocomposites Based on Polypropylene Random Copolymer and Ethylene–Propylene Block Copolymer

Reactive Extrusion of Multifunctional Conducting Nanocomposites Based on Polypropylene Random Copolymer and Ethylene–Propylene Block Copolymer

Effect of surface anodizing on the bonding properties of aluminum alloy/glass-fiber reinforced polypropylene random copolymer hybrid joints

Polymer-metal hybrid (PMH) joints of glass-fiber reinforced polypropylene random copolymer (GFRPPR) and aluminum alloy were prepared by the self-made hot pressing technology (HPT). The PPR copolymer was grafted with maleic anhydride and reinforced with 30% short glass fiber, and the aluminum alloy surface was anodized in oxalic acid and phosphoric acid solution, respectively. The PMH interfaces were mainly characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle tests. Anodized in the phosphoric acid solution, the anodized aluminum alloy surface showed needle-shaped honeycomb-like microstructures. The phosphoric acid anodized aluminum alloy surface was beneficial for polymer melt to flow into and form interlocking microstructures due to its micro porous structure, and the corresponding tensile shear strength and work of fracture reached up to 10.88 MPa and 16.15 kJ m−2, respectively.

Temperature dependent degradation of phenolic stabilizers and ageing behaviour of PP-R micro-specimen

This paper deals with the hot air ageing behaviour of a polypropylene random copolymer (PP-R) model material in a wide temperature range from 65 to 135°C. The PP-R grade was stabilized with a blend of the phenolic antioxidants Irganox 1330 and 1010. To avoid diffusion-limited oxidation effects, micro-specimen with a thickness of 100 µm were investigated. As main ageing indicator the phenol index was evaluated from FTIR-spectra in transmittance mode. The oxidation of the functional phenolic groups was associated with a shift of the absorption peak by 18 and 35 cm-1 of the single- and dual-oxidized phenolic antioxidant Irganox 1330. The implemented FTIR evaluation approach was validated by high-pressure liquid chromatography hyphenated with mass spectroscopy and ultraviolet detection. Gaussian fitting of the triple IR-peak confirmed temperature dependent differences in the degradation pathways of the phenolic antioxidants. The decay of phenol index and the obtained endurance time exhibited a bilinear Arrhenius like behaviour with a transition temperature at 110°C, which was in agreement with the onset of melting of small crystal lamellae. The activation energy values were 94 and 32 kJ mol-1 above and below the transition temperature, respectively.

Comparative study on annealing‐induced high‐impact toughness of linear and grafted polypropylene random copolymer

AbstractIn present work, the comparative study on annealing‐induced high‐impact toughness of linear and grafted polypropylene random copolymer (PPR and MPP) was performed. The changes of microstructure and mechanical properties of PPR and MPP upon annealing were investigated in detail. The results showed that maleic anhydride was grafted onto the backbone of PPR to form long‐chain branched structure. During the melt grafting process, the degradation reaction is dominant, giving rise to the decrease in molecular weight and degree of chain entanglement, and hence PPR demonstrates higher flexural modulus and impact strength, as well as lower elongation at break than MPP. The long‐branched chains perform the function of heterogeneous nucleation. The depressed chain entanglement facilitates the diffusion of polymer chains during the crystallization process, followed by higher total crystallization rate and crystallinity of MPP in contrast to those of PPR. Thermal annealing treatment promotes the secondary crystallization, and hence the crystallinity and crystal perfection of the polymer is elevated, resulting in enhanced mobility of the chain segments in the amorphous region. After annealing at 100°C for 3 h, the impact strength of MPP is 71% higher than that of its unannealed counterpart, while this value is increased remarkably by 153% for PPR. The existence of long‐branched chains may not be conducive to sufficient rearrangement of chain segments of MPP during the annealing treatment. As a consequence, the crystallinity and impact strength of PPR are elevated more pronouncedly in comparison with those of MPP after annealing treatment.