Statistical properties of interparticle/void distance for amorphous plastics toughening

Statistical properties of interparticle/void distance (ID) for various particle/void and dispersion types are studied in relation with toughening of plastics using computer‐generated three‐dimensional models. Particle/void size groups adopted were either of constant diameter or of log‐normal distribution. Particles/voids were dispersed at uniform‐random or flocculated with multiple clusters. It was found that IDs are (a) of approximately Gaussian distribution for particles/voids of either a constant diameter or a log‐normal distribution, when they are dispersed at uniform‐random, but (b) not of Gaussian distribution for particle/void sizes of bimodal log‐normal distribution, nor for flocculated log‐normal distribution of particles/voids dispersed with multiple clusters. It was also found that the degree of ID uniformity for a single group of log‐normally sized particles/voids is not sensitive to standard deviation of particle/void size. Mixing effect on ID properties using two groups of log‐normally distributed particles/voids with similar mean particle/void diameters was simulated. It was found that, when a significant amount (36 vol %) of particles/voids of a small mean and standard deviation of ID was mixed with a group of particles/voids of a large mean and standard deviation of ID, mean and standard deviation of ID for the mixture were not substantially lower than those of the group of particles/voids of the large mean and standard deviation of ID. It was also found that the degree of ID uniformity for the mixture of the two groups was lower than those of individual groups, indicating that the mixing has deleterious effect on toughening. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4256–4262, 2006     

ABS树脂增韧机理

介绍了国内外对丙烯腈-丁二烯-苯乙烯共聚物(ABS)增韧机理的研究情况,分析了ABS结构特点,讨论了ABS增韧机理,分析了橡胶空洞化对应增韧作用的贡献,研究了银纹、多重银纹及剪切带对增韧的作用,总结了橡胶数量、凝胶、粒径等对增韧效果的影响.     

Deformation mechanism of polystyrene toughened with sub‐micrometer monodisperse rubber particles

Core–shell polybutadiene‐graft‐polystyrene (PB‐g‐PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core‐shell rubber particles were then blended with polystyrene to prepare PS/PB‐g‐PS blends with a constant rubber content of 20 wt%. PB‐g‐PS particles with a lower PB/PS ratio (≤70/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high‐impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1–3 µm rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub‐micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress‐whitening zone of blends with a PB/PS ratio of 70/30 in PB‐g‐PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation. Subsequently, a compression‐induced activation method was explored to compare the PS/PB‐g‐PS blends with commercial HIPS, and the result show that the toughening mechanisms of the two samples are different. Copyright © 2006 Society of Chemical Industry     

双马来酰亚胺／聚醚酰亚胺共混体系的增韧改性研究

研究了有机硅烷偶联剂对双马／聚醚酰亚胺共混体系的增容增韧作用。结果表明,加入有机硅烷偶联剂KH-550、KH-560、偶联剂B后,共混物断裂韧性（G1c）均有大幅度提高,其中偶联剂B增韧效果最佳;当B的添加量为2．5份时,体系的断裂韧性最大,达到1053J／m^2,为改性前的3．9倍,体系的微观形貌（SEM）由改性前的两相结构转变为双连续相结构。     

Effect of polystyrenes with different architectures on the β‐nucleating efficiency and toughening of isotactic polypropylene

The effect of polystyrenes (PSs) with different architectures (three‐arm star‐shaped polystyrene (sPS), comb‐like branched polystyrene (cPS) and linear polystyrene) on their β‐nucleating efficiency for isotactic polypropylene (iPP) during crystallization and final impact and the tensile properties of iPP/PS blends were investigated by dynamic rheological measurements, SEM, DSC, polarized optical microscopy, wide angle X‐ray diffraction and mechanical property measurements. The results show that the architecture of PS has marked influence on its dispersibility in iPP and β‐nucleating efficiency. For iPP/cPS blend, plenty of short side chains reduce the probability of cPS chain entanglements, facilitating the interdiffusion between iPP and cPS chains. A favorable interfacial interaction results in good dispersibility, high β nucleating efficiency and an excellent toughening effect of cPS on iPP. However, the relatively high chain entanglement degree of sPS may not be in favor of chain diffusion between iPP and sPS and therefore relatively poor dispersibility and toughening effect are obtained. The elongation at break and impact strength of iPP were dramatically improved, especially with the addition of 1 wt% cPS. The toughening mechanism of PS on iPP is the dissipated energy caused by cavitation and the β‐nucleating effect of PS. © 2018 Society of Chemical Industry     

Structure,mechanical, and fracture properties of nanoreinforced and HNBR‐toughened polyamide‐6

Hydrogenated nitrile rubber (HNBR) and synthetic nanofillers, viz. water‐swellable sodium fluorohectorite (FH) and water dispersible boehmite alumina (BA), were used to toughen and reinforce polyamide‐6 (PA‐6). FH and BA were introduced in HNBR latex that was dried prior to melt mixing with PA‐6. Binary blend (PA‐6/HNBR) and ternary nanocomposites (PA‐6/HNBR/nanofiller) were produced and their structure–property relationships studied. HNBR was coarsely and microscale dispersed in PA‐6. FH, slightly intercalated, was present in PA‐6 and in the PA‐6/HNBR interphase, whereas BA was mostly located in the HNBR droplets. HNBR improved the ductility of the PA‐6/HNBR blend at cost of stiffness and strength. The fracture toughness and energy, determined on notched Charpy specimens at different temperatures (T = ?30°C, room temperature, and T = 80°C) were improved by blending with HNBR at 9 wt %. Additional incorporation of the nanofillers in 2.5 wt % enhanced the stiffness and strength of the PA‐6/HNBR blend but reduced its ductility. The fracture toughness of the ternary nanocomposites was between those of PA‐6 and PA‐6/HNBR, whereas their fracture energy fairly agreed with that of the parent PA‐6. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Intercalation structure and toughening mechanism of graphene/urea‐formaldehyde nanocomposites prepared via in situ polymerization

Based on the industrialized graphene (GN) product, a series of graphene/urea‐formaldehyde nanocomposites were synthesized via in situ polymerization by incorporation of silicon coupling agent with terminal amino groups (SA) as the compatibilizer. The results showed that addition of SA coupling agent led to much more efficient grafting of UF molecules on the GN surface with high layer thickness by formation of hydrogen bonding, and thus complete exfoliation and uniform dispersion of GN were achieved for the composites. Compared with neat UF, the addition of 1.0 wt% GN resulted in a roughly 25% increase in tensile strength and 12% increase in impact strength; meanwhile the impact fracture surfaces of the composite showed obvious ductile fracture characteristics, indicating the reinforcing and toughening effect of GN on the UF matrix. With increasing GN content, the storage modulus, glass transition temperature and crosslinking density of UF increased, while the tan δ_max decreased, suggesting that a double crosslinking network structure with GN centered crosslinking point and chemical crosslinking point of UF molecular chains formed, leading to improvement in the stiffness of the composites. The present work showed promising potential for developing high performance UF resin on an industrial scale. © 2017 Society of Chemical Industry     

Curing and toughening of a styrene‐modified epoxy resin

A commercially available epoxy resin (E907) formulated with a viscosity‐reducing styrene monomer and several additives was subjected to thermal cure studies and mechanical property measurements. Thermoplastic poly(arylene ether sulfone) (PES) and poly(arylene ether phosphine oxide) (PEPO) with reactive amine or hydroxyl end groups were utilized to toughen and co‐cure with the system. The cure cycle was optimized and the networks were analyzed via differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analyzer, scanning electron microscopy, sol–gel extractions, and fracture toughness. A model epoxy resin was prepared from a tetrafunctional epoxy, e.g., MY722, difunctional EPON828, styrene monomer, and benzoyl peroxide initiator (BPO), and was evaluated as a control to assess the possible role of the styrene monomer. The optimized cure cycle for E907 was 6 h at 93°C, followed by a postcure of 2 h at 204°C. The fracture toughness of E907 was increased only marginally with PES and PEPO. In contrast, the model epoxy resin demonstrated a positive effect due to the styrene monomer and BPO and exhibited significantly increased fracture toughness with PES modification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1504–1513, 2001     

Multiscale toughening of ZrB2-SiC-Graphene@ZrB2-SiC dual composite ceramics

The design of bioinspired architectures is effective for increasing the toughness of ceramic materials. Particularly, a dual composite equiaxial architecture is ideal for fabricating weak interface-toughened ZrB₂-SiC ceramics with isotropic performance. In this paper, ZrB₂-SiC-Graphene@ZrB₂-SiC dual composite ceramics were synthesized via an innovative processing technique of granulating-coating method. ZrB₂-20 vol.% SiC containing 30 vol.% Graphene was selected as weak interface to realize multiscale toughening and improve the thermal shock resistance of ZrB₂-SiC ceramic materials. The incorporation of ZrB₂-SiC-Graphene weak interface into the ZrB₂-SiC matrix improved the damage tolerance and critical thermal shock temperature difference. The design of equiaxial structures moderated the anisotropy of performance in different planes. The graphene sheets incorporated in the ZrB₂-SiC-Graphene interface phase played a key role in multiscale toughening, including macroscopic toughening of crack deflection and microcracks, and microscopic toughening of graphene bridging and pull-out.     

Time‐resolved small‐angle X‐ray scattering study of void fraction evolution in high‐density polyethylene during stress unloading and strain recovery

By means of time‐resolved small‐angle X‐ray scattering, we developed an analysis methodology to assess the void volume fraction ?_v in high‐density polyethylene (HDPE) during tensile testing. The specimens were first drawn up to different imposed strains, and subsequently were subjected to stress unloading and strain recovery stages. During the loading stage, ?_v progressively increased with the strain level, starting from a well‐defined onset strain prior to the yield point. In particular, ?_v reached a maximum of 8.75 vol% for a strain of 12.5% in the case of a HDPE grade with a molecular weight of 105 000 g mol^?1. Stress unloading and strain recovery caused a decrease in ?_v attained at the end of the loading stage. For a HDPE grade with a molecular weight of 55 000 g mol^?1, ?_v was more important during the loading stage and the decrease in ?_v was less marked during the stress unloading stage when compared to the HDPE with molecular weight of 105 000 g mol^?1. The residual and reversible components of void volume fraction were revealed. © 2015 Society of Chemical Industry     

“Ex situ” concept for toughening the RTMable BMI matrix composites,Part I: Improving the interlaminar fracture toughness

Aerospace‐grade bismaleimide matrix composites was toughened based on a novel ex situ resin transfer molding (RTM) technique using a special manufactured ES? carbon fabrics. The toughening mechanism and toughening effect by the technique are studied using thermoplastic PAEK as toughener. Mode I fracture toughness (G_IC) of the composites toughened by ex situ RTM technique increased up to three times higher than that of the control system, and Mode II fracture toughness (G_IIC) increased two times higher as well. The composite without toughening was denoted as control system. The microstructure revealed that a reaction‐induced phase decomposition and inversion happened in the interlaminar region, which resulted in a particles morphology that showed the thermosetting particles were surrounded with the PAEK phase. The plastic deformation and rupture of the continuous PAEK phase are responsible to the fracture toughness improvement. And the influence of PAEK concentration on toughness improvement was also investigated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of aliphatic amine epoxy hardener on the adhesive properties of blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with epoxy resin

The adhesive properties have been investigated in blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with diglycidyl ether of bisphenol A and three different aliphatic amine epoxy hardener. The adhesives properties are evaluated in steel alloy substrate using single‐lap shear test. The copolymers are initially miscible in the stoichiometric blends of epoxy resin and hardener at room temperature. Phase separation is noted in the course of the polymerization reaction. Different morphologies are obtained according to the amine epoxy hardener. The most effective adhesive for steel–steel joints in single‐lap shear test is the blends using 1‐(2‐aminoethyl)piperazine (AEP) as hardener. This system shows the biggest lap shear strength. However, the modified adhesives show a reduction in the mechanical resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Use of acrylate‐based liquid rubbers as toughening agents and adhesive property modifiers of epoxy resin

Carboxyl‐randomized poly(2‐ethyl hexyl acrylate) (CRPEHA) and epoxy‐randomized poly(2‐ethylhexyl acrylate) (ERPEHA) were synthesized by solution polymerization technique in the form of liquid rubbers. The liquid rubbers were characterized by IR and ¹H‐NMR spectroscopic analysis, nonaqueous titration, and GPC. The liquid rubbers were pre‐reacted with the epoxy resin and the modified epoxy networks were made by curing with an ambient temperature curing agent. The modified epoxy networks containing different concentrations of CRPEHA (A‐1) and ERPEHA (B‐1) were evaluated with respect to their thermal and impact properties. The optimum properties were obtained at 10‐phr concentration of a (1 : 1) mixture of CRPEHA and ERPEHA. Fracture surface analysis by scanning electron microcopy indicated the presence of a two‐phase microstructure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3814–3821, 2004     

Influence of phase structure on impact toughening of isotactic polypropylene by metallocene‐catalyzed linear low‐density polyethylene

In the present study isotactic polypropylene (PP) and metallocene‐catalyzed linear low‐density polyethylene (mLLDPE) were blended together to obtain thermoplastic materials (compositions) with improved toughness. Structure–property relationships were determined for these compositions with the help of scanning electron microscopy (SEM). Special emphasis was made on tracing the morphological features that led to the optimum mechanical performance. A co‐continuous type of structure was found to have much superior toughness as compared to a dispersed‐matrix structural type, for blends comprised of the same components (PP and mLLDPE). The study showed the fascinating possibility of creating toughened PP blends by inducing a co‐continuous structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1011–1018, 2000     

Synthesis and evaluation of liquid amine‐terminated polybutadiene rubber and its role in epoxy toughening

Epoxy resin is widely used for coatings, adhesives, castings, electrical insulation materials, and other applications. However, unsolved problems still remain in its applications. The main problem is low toughness: cured epoxy resin is rather brittle, with poor resistance to the propagation of cracks derived from the internal stress generated by shrinkage in the cooling process from cure temperature to room temperature. The objective of this study was to improve the flexibility and toughness of diglycidyl ether of bisphenol A based epoxy resin with a liquid rubber. For this purpose, amine‐terminated polybutadiene (ATPB) was synthesized. The product was characterized by Fourier transform infrared and NMR spectroscopy and elemental analysis. ATPB‐modified epoxy networks were made by curing with an ambient‐temperature curing agent, triethylene tetramine. We varied the epoxy/liquid rubber compositions to study the effect of toughener concentration on the impact and thermal properties. Higher mechanical properties were obtained for epoxy resins toughened with 1 phr ATPB. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2446–2453, 2005     

Mechanical properties of epoxy resin/hydroxyl‐terminated polyester blends: effect of two‐phase structure

In this paper, the effect of two‐phase structure on the mechanism of rubber‐toughening of epoxy resins was studied. Three types of hydroxyl‐terminated polyesters with different molecular weights were synthesized in order to modify epoxy resins to obtain single‐phase (P‐1), critical phase separation (P‐2) and two‐phase (P‐3) structures. The results of dynamical mechanical analysis and scanning electron microscopy distinguished the dissolved and phase‐separated polyesters in the epoxy matrix. The P‐1 system showed the highest dissolved content of polyester in the epoxy matrix, while the P‐3 system exhibited the lowest content. Both dissolved and phase‐separated polyesters proved to be capable of increasing the toughness of modified epoxy resins. The phase‐separated polyester was found to contribute much more to the improvement of toughness. Copyright © 2005 Society of Chemical Industry     

环氧树脂增韧新途径及增韧机理的研究

介绍了环氧树脂通过共聚共混法增韧改性的一些新方法,包括热塑性树脂增韧、互穿网络聚合物增韧、热致液晶聚合物增韧、刚性高分子增韧、核壳结构聚合物增韧等,并分别对其增韧机理作了总结分析。     

Core–shell particles designed for toughening poly(vinyl chloride)

A novel core–shell modifier (MOD) made up of polystyrene and poly(butyl acrylate) (PBA) grafted on a crosslinked styrene‐co‐butadiene core was synthesized by emulsion polymerization. This modifier was used for enhancing effectively the impact ductility of poly(vinyl chloride) (PVC) without losing its transparency. The effects of the MOD on the properties of PVC/MOD blends were explored. It was found that the butyl acrylate (BA) content of the MOD was an important factor affecting the properties of PVC/MOD blends. The Izod impact strength of these blends reached 1200 J m^?1 when the MOD contained 40 wt% BA. The dispersion morphology of the MOD in the PVC matrix was investigated using transmission electron microscopy, with a uniform dispersion of the MOD with higher BA content being obtained. The toughening mechanism of PVC/MOD blends was also investigated. The presence of BA in the MOD enhanced the ductility of the PVC blends due to the increased amount of soft phase (PBA). The dispersion morphology indicated that the interfacial interaction between MOD particles and PVC matrix was improved due to the presence of PBA graft chain in the MOD. TEM of impact fracture samples showed that shear yielding of the PVC matrix and debonding of MOD particles were the major toughening mechanisms for the PVC/MOD blends. Copyright © 2010 Society of Chemical Industry     

环氧胶粘剂的韧性与增韧机理

本文通过测定三种典型环氧结构胶粘剂：环氧-聚矾，环氧-丁腈40环氧-CTBN的动态力学性能，剥离强度和断裂韧性，观察其断面的电镜照片，分析了三者不同的韧性特点和增韧机理。并发现了PSF改性胶固化后奇特的两相结构。     

Crack‐healing behavior of epoxy–amine thermosets

This work offers detailed experimental evidence for crack healing in fully formed epoxy–amine polymer networks. Compact tension specimens of diglycidyl ether of bisphenol A (EPON‐828) and 4,4′‐methylene biscyclohexanamine were synthesized at stoichiometry and with an excess or paucity of an amine curing agent. Healing efficiencies were measured on the basis of the regain in the fracture load after a healing protocol was applied. For all systems investigated, the average healing efficiency for first fracture was greater than 50% when healing was conducted at 185°C for 1 h. The crack‐healing behavior was highly repeatable at all stoichiometries, and healing was found to occur for repeated fracture–heal cycles of the same specimen. On the basis of results from size exclusion chromatography for the extractable phase, infrared spectroscopy, and scanning electron microscopy, it is postulated that healing is primarily due to mechanical interlocking of the nodular topology of a fractured crack interface that occurs in the rubbery state and is set in place by vitrification upon cooling. A ½ power dependence of the healing efficiency on the healing time was observed, and this suggests that the interlocking of topographical features is governed by diffusive processes. For networks cured with a large excess of epoxide groups, the recovered fracture load was higher than that of virgin specimens. In this case, polyetherification or homopolymerization of previously unreacted epoxy groups increased the healing efficiency significantly, and this suggests that low degrees of covalent bonding can significantly enhance healing behavior in these systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009