Exploring the thermomechanical properties of peroxide/co-agent assisted thermoplastic vulcanizates through temperature scanning stress relaxation measurements

Temperature scanning stress relaxation (TSSR) measurement of peroxide vulcanized polymer blends of polypropylene (PP) and ultrahigh molecular-EPDM (UHM-EPDM) rubber has been performed to study the thermomechanical behavior of thermoplastic vulcanizates (TPVs). Co-agents play crucial roles in the enhancement of properties of TPVs. Different types of co-agents (Triallyl cyanurate-TAC; N, N-m-phenylene-dimaleimide-HVA2; zinc dimethacrylate-ZDMA; and in-situ formed zinc dimethacrylate-ZMA) have been explored in this work. TSSR study shows that higher T₅₀ and T₉₀ values have been achieved in ZMA co-agent assisted-TPV. Higher TSSR-index (RI) value was also found for the same co-agent ZMA, indicating higher elastic behavior. TSSR result supports the mechanical and rheological properties, and it is found that the ZMA and ZDMA show higher mechanical strength. Cross-linked-density calculated by modified Flory–Rehner equation and the cross-link-density as obtained from TSSR method have been compared and the trend was found to be the same. Stress relaxation study shows the slow relaxation-phenomena of the ZMA-TPV with slowest relaxation-time (θ_r) than the other TPVs, which correlates with superior material strength. Thermogravimetric analysis proves that there is a difference in degradation temperature of the blends at approximately 5–10°C. Ultrahigh molecular weight-EPDM/PP based TPVs reveal superior thermomechanical and physico-mechanical properties with ZMA and ZDMA co-agent over TAC and HVA2. These ultrahigh molecular weight-EPDM based TPVs can be used in automotive seals/strips, hoses, bellows, and 2 K-molds for automotive applications.     

三种不同硫化助剂对MVQ/EPDM共混胶性能的影响

研究了3种硫化助剂对MVQ/EPDM共混胶硫化特性、力学性能、耐热老化性能、高温压缩永久变形性能及动态力学性能的影响。结果表明,添加硫化助剂HVA—2的共混胶焦烧时间和正硫化时间均明显缩短;添加硫化助剂丁羟胶和TAIC的共混胶焦烧时间和正硫化时间均变化不大;添加硫化助剂丁羟胶的共混胶具有最好力学性能、耐热老化性能和压缩永久变形性能,其玻璃化温度也比空白样的低近3℃。     

Influence of accelerator/sulphur and co-agent/peroxide ratios in mixed vulcanisation systems on cure characteristics,mechanical properties and heat aging resistance of vulcanised SBR

The influence of accelerator/sulphur and co-agent/peroxide ratios on cure characteristic and vulcanisate properties in mixed vulcanisation of styrene butadiene rubber (SBR) was investigated in this work. Accelerator/sulphur ratio was investigated with three alternative sulphur curing systems, namely conventional, semi-efficient and efficient vulcanisation (EV) systems. Zinc dimethacrylate (ZDMA) was used as a co-agent to enhance the performance of peroxide and to provide ionic linkages. Ionic linkages contributed by ZDMA create bridges between two polymer chains. The ZDMA/peroxide ratio was varied from 2 to 10. The concentration of dicumyl peroxide was held fixed while the ZDMA content was varied. Cure characteristics, mechanical properties, dynamic mechanical properties and heat aging resistance were investigated in relation to the crosslink structure. Increasing the ZDMA/peroxide ratio significantly increased density of ionic linkages, especially in combination with the EV system. The combination of EV system with high ZDMA/peroxide ratio provided the highest ionic crosslink density and the lowest polysulphidic crosslink density: this enhanced the mechanical properties, the dynamic mechanical properties and the thermal stability of SBR vulcanisates.     

Enhancement of processability and foamability of ground tire rubber powder and LDPE blends through solid state shear milling

The foamed composites made from low-density polyethylene(LDPE) and ground tire rubber(GTR) powder using azodicarbonamide as chemical blowing agent have been investigated. Solid state shear milling was used to enhance the processability and foamability of LDPE/GTR blends by a pan-mill type mechanochemical reactor. First the blends of LDPE/GTR were prepared by co-milling, then the samples were melt-mixed in a Brabender Plasti-Corder, saturated with blowing agent, crosslinking agent and blowing co-agent, and finally the saturated specimens were expanded during the pressure-quench process. The results indicated that the mechanical properties of the LDPE/GRT foamed composites were improved, and the blends of co-milled GTR and LDPE powder showing better processability and foamability than those obtained in a conventional melt-mixing manner, as indicated by the rheological and morphological studies.     

Investigation on two modification strategies for the reinforcement of biodegradable lignin/poly(lactic acid) blends

In this work, biodegradable lignin/poly(lactic acid) (PLA) blends were prepared with melting compounding method. Dicumyl peroxide (DCP) and maleic anhydride (MA)/biphenyl peroxide (BPO) were used for the modification of the polymer blends, respectively. Structure of the polymer blends was characterized with Fourier transformed infrared spectroscopy and field emission scanning electron microscopy. Mechanical properties of the samples were determined with universal test machine and dynamic mechanical analysis. Thermal behaviors and thermal stability of the blends were all characterized with a thermal gravimetric analysis/differential scanning calorimetry simultaneous thermal analyzer. Lignin reinforced the mechanical strength of the blends while the thermal stability was not improved. At low content, DCP and MA/BPO apparently enhanced the mechanical strength of lignin/PLA blends. However, excessive DCP led to decreased tensile strength and elongation at break. Both DCP and MA/BPO resulted in lower glass transition temperature and melting temperature of PLA in the blends, while the thermal stability of the polymer blends was poorer after modification.     

Mechanical properties of uncrosslinked and crosslinked linear low‐density polyethylene/wax blends

The mechanical properties of uncrosslinked and crosslinked linear low‐density polyethylene (LLDPE)/wax blends were investigated, using differential scanning calorimetry (DSC), tensile testing, and melt flow indexing. A decrease in the degree of crystallinity, as determined from the DSC melting enthalpies, was observed with an increase in the dicumyl peroxide (DCP) concentration. The Young's modulus increased with increased wax portions, and there was a higher increase for crosslinked blends. The yield stress generally decreased with increased peroxide content. Crosslinking caused an increase in elongation at yield, but increased wax content caused a decrease in elongation at yield. The stress at break generally increased with increasing peroxide content, but it decreased with increased wax content. The elongation at break decreased with an increase in the DCP concentration. Melt flow rate measurements indicated a mutual miscibility in LLDPE/wax blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 973–980, 2001     

Cure characteristics and mechanical properties of hydrogenated natural rubber/natural rubber blends

The cure characteristics and mechanical properties of blends consisting of hydrogenated natural rubber (HNR) and natural rubber (NR) blends were investigated. The HNR/NR blends at 50/50 wt ratio were vulcanized using various cure systems: peroxide vulcanization, conventional vulcanization with peroxide, and efficient vulcanization with peroxide. The HNR/NR vulcanizates cured by the combination of peroxide and sulfur donor (tetramethylthiuram disulfide, TMTD) in the efficient vulcanization with peroxide exhibited the best mechanical properties. It was also found that the hydrogenation level of HNR did not affect the tensile strength of the vulcanizates. The tensile strength of the blends decreased with increasing HNR content because of the higher incompatibility to cause the noncoherency behavior between NR and HNR. However, the HNR/NR vulcanizate at 50/50 wt ratio showed the maximum ultimate elongation corresponding to a co‐continuous morphology as attested to by scanning electron micrographs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tailoring the morphology and properties of poly(lactic acid)/poly(ethylene)‐co‐(vinyl acetate)/starch blends via reactive compatibilization

Poly(lactic acid)/poly(ethylene‐co‐vinyl acetate)/starch (PLA/EVA/starch) ternary blends were prepared by multi‐step melt processing (reactive extrusion) in the presence of maleic anhydride (MA), benzoyl peroxide and glycerol. The effects of MA and glycerol concentration on the morphology and properties of the PLA/EVA/starch blends were studied using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, the Molau experiment, dynamic mechanical thermal analysis and differential scanning calorimetry etc. The plasticization and compatibilization provided a synergistic effect to these blends accompanied by a significant reduction in starch particle size and an increase in interfacial adhesion. Starch was finely dispersed in the ternary blends with a dimension of 0.5 ? 2 µm. Furthermore, EVA‐coated starch or a starch‐in‐EVA type of morphology was observed for the reactively compatibilized PLA/EVA/starch blends. The EVA with starch gradually changed into a co‐continuous phase with increasing MA concentration. Consequently, the toughness of the blends was improved. Since property stability of starch is an issue, the tensile properties of these blends were measured after different storage times and the blends showed good property stability. Copyright © 2012 Society of Chemical Industry     

Influence of static and dynamic crosslinking techniques on the transport properties of ethylene propylene diene monomer rubber/poly (ethylene-co-vinyl acetate) blends

The transport characteristics of dynamically and statically cross-linked Ethylene Propylene Diene Monomer/poly (ethylene-co-vinyl acetate) (EPDM/EVA) blends have been examined in the temperature interval of 28–58 °C using benzene, toluene and xylene as probe molecules. The dynamically vulcanized blends exhibited enhanced properties on the sorption and diffusion features compared to the corresponding statically vulcanized blends. In both the cases, as the EVA content increased in the blends, the solvent uptake decreased. The experimental observations have been correlated with the phase morphology of the blends, using scanning electron micrographs. The crystallinity of the blends was studied using X-ray diffraction patterns. Among the three vulcanising systems, viz, sulphur, dicumyl peroxide (DCP), and a mixture consisting of sulphur and peroxide, employed for the matrix, the DCP cross linked system exhibited the lowest solvent uptake. The molar mass between cross links and the diffusion coefficients have been computed to complement the observed sorption behaviour.     

In situ compatibilization of polypropylene/polystyrene blend by controlled degradation and reactive extrusion

In situ compatibilization of polypropylene (PP) and polystyrene (PS) was achieved by combinative application of tetraethyl thiuram disulfide (TETD) as degradation inhibitor and di‐tert‐butyl peroxide as degradation initiator in the process of reactive extrusion. The PP/PS blends obtained were systematically investigated by rheological measurement, scanning electron microscopy, and differential scanning calorimetry. The results indicate that peroxide‐induced degradation of PP can be effectively depressed by adding TETD, which may favor the formation of PP‐g‐PS copolymer during melt processing. The PP‐g‐PS copolymer formed may act as an in situ compatibilizer for PP/PS blends, and subsequently decreases the size of dispersed PS phase and changes both rheological and thermal properties of the blends. Based on the present experimental results, the mechanisms for the controlled degradation of PP and in situ formation of PP‐g‐PS copolymer in the PP/PS blends have been proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

低发泡倍率硅橡胶海绵结构及性能的影响因素

简要介绍了过氧化二苯甲酰硫化的低发泡倍率硅橡胶海绵胶料的配方、制备方法、海绵结构及力学性能。结果表明,硫化剂用量、硫化助剂、发泡温度、胶料可塑度和生胶相对分子质量对海绵硫化发泡效果的影响较大。硫化助剂会影响海绵的硫化返原,而胶料温度对海绵密度和硬度有一定的影响。低发泡倍率海绵为典型的闭孔结构,海绵压缩量大,模量低,拉伸强度低（〈0.8MPa）,伸长率高,压缩永久变形小,应力伸长率大,回弹性优。     

Mechanical properties and morphology of crosslinked PP/PE blends and PP/PE/propylene–ethylene copolymer blends

Blending is an effective method for improving polymer properties. However, the problem of phase separation often occurs due to incompatibility of homopolymers, which deteriorates the physical properties of polyblends. In this study, isotactic polypropylene was blended with low-density polyethylene. Crosslinking agent and copolymers of propylene and ethylene (either random copolymer or block copolymer) were added to improve the interfacial adhesion of PP/LDPE blends. The tensile strength, heat deflection temperature, and impact strength of these modified PP/PE blends were investigated. The microstructures of polyblends have been studied to interpret the mechanical behavior through dynamic viscoelasticity, wide-angle X-ray diffraction, differential scanning calorimetry, picnometry, and scanning electron microscopy. The properties of crosslinked PP/PE blends were determined by the content of crosslinking agent and processing method. For the material blended by roll, a 2% concentration of peroxide corresponded to a maximum tensile strength and minimum impact strength. However, the mechanical strength of those products blended by extrusion monotonously decreased with increasing peroxide content because of serious degradation. The interfacial adhesion of PP/PE blends could be enhanced by adding random or block copolymer of propylene and ethylene, and the impact strength as well as ductility were greatly improved. Experimental data showed that the impact strength of PP/LDPE/random copolymer ternary blend could reach as high as 33.3 kg · cm/cm; however, its rigidity and tensile strength were inferior to those of PP/LDPE/block copolymer blend.     

硅烷接枝交联法制备发泡用高熔体粘度聚丙烯

以过氧化物为引发剂,不饱和硅烷为接枝单体,不饱和烃类为接枝助剂,并加入交联催化剂,通过反应型双螺杆挤出机一步实现共聚型聚丙烯的接枝和交联;制备出了可用于发泡的高熔体粘度聚丙烯。通过熔体质量流动速率(MFR)和凝胶含量的变化,研究试剂体系对接枝交联改性的作用。结果显示,改性后PP的MFR可降低至0．1 g／ 10min以下,凝胶含量可高达48％以上,体系中各组分都显著影响改性材料熔体的流动性和凝胶含量,缺一不可。随引发剂和硅烷单体含量的增加,体系熔体流动性逐渐降低,凝胶含量增加。而硅烷单体与接枝助剂的最佳量之比为1 :1。通过PP改性前后的力学性能和发泡性能对比研究表明,接枝和交联使改性后PP的耐热性、抗冲击性、拉伸性能均有所改善;而且用改性PP发泡可以获得泡孔均匀、细密,且具有独立泡孔的高质量泡沫塑料。     

The effect of mercapto‐modified ethylene–vinyl acetate (EVA) on curing parameters,mechanical properties,and thermal properties of vulcanized styrene–butadiene rubber (SBR)/EVA blends

The effect of EVA functionalized with mercapto groups (EVALSH) on the compatibilization of SBR and EVA copolymer blends was investigated in vulcanized systems based on sulfur or dicumyl peroxide (DCP). The presence of EVALSH resulted in an improvement of the tensile properties, indicating the reactive compatibilizing effect of this compound. The best mechanical performance was achieved with the sulfur‐curing system for both compatibilized and noncompatibilized blends. The blend systems were also analyzed by scanning electron microscopy, differential scanning calorimetry, and dynamic‐mechanical analysis. The crystallinity of the EVA phase was significantly affected by the presence of the EVALSH, whereas no substantial change was detected on the damping properties or the glass transition temperature of the SBR phase. Considering the aging properties, the presence of EVALSH increases the thermal stability of the blends vulcanized with DCP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 239–249, 2002     

Improved Performance of Environmentally Friendly Blends of Biobased Polyethylene and Kraft Lignin Compatibilized by Reactive Extrusion with Dicumyl Peroxide

In this work, different contents (0.25, 0.50, 0.75, and 1 phr) of dicumyl peroxide (DCP) are incorporated into the bio-based high-density polyethylene (bioPE)/kraft lignin (KL) blends with a composition of 80 and 20 wt%, respectively with the aim of improving overall performance. The samples are obtained by reactive extrusion and injection-molding process, and then their overall performance is assessed by tensile tests, thermal analysis, optical and surface appearance, and wettability studies. The obtained mechanical properties confirm the successful interaction between bioPE and KL due to the addition of organic peroxide, which plays a key role in compatibilization. In particular, bioPE/KL blends with 1 phr of DCP achieve an increase in elongation at break of about 300% together with a noticeable increase in the impact strength of about 29% higher than the uncompatibilized bioPE/KL blend, while the tensile modulus decreases 42%. In addition, images obtained by field emission scanning electron microscopy show that the presence of DCP in the blends enhances better dispersion of KL into the bioPE matrix. The wettability analysis indicates that KL and DCP affect the hydrophobicity of the neat bioPE. Therefore, the resultant blends can be considered as potential sustainable polymers with balanced properties.     

噻二唑硫化体系对氯化聚乙烯橡胶性能的影响

研究噻二唑硫化体系(硫化剂PT75/促进剂903体系)对氯化聚乙烯橡胶(CM)性能的影响。结果表明:与过氧化物硫化体系(过氧化物BIPB/助交联剂TAIC体系)胶料相比,噻二唑硫化体系胶料的拉伸性能和抗撕裂性能大大改善,耐热老化性能相当,耐油性能较好;硫化剂PT75和促进剂903用量比为2/2时,胶料的压缩永久变形较小,拉伸性能和抗撕裂性能较好,耐热老化性能优异。     

The effect of peroxide crosslinking on thermal,mechanical, and rheological properties of polycaprolactone/epoxidized natural rubber blends

Polycaprolactone (PCL)/epoxidized natural rubber (ENR) blends (PCL/ENR = 70/30, 50/50 wt/wt) were prepared by a melt mixing in an internal mixer in the presence of a small amount (0.5 and 1 phr) of dicumyl peroxide. The effect of peroxide crosslinking on thermal, mechanical, and rheological properties of the blends was investigated by means of DSC, tensile test, and small amplitude oscillating rheometer, respectively. It was revealed that peroxide crosslinking enhanced degree of crystallinity of PCL phase and its non-isothermal melt crystallization temperature. The crosslinked blends behave like a thermoplastic elastomer exhibiting high elongation-at-break and fairly good elastic recovery as well as melt processibility. From melt rheological analysis, the peroxide crosslinked blends showed more pronounced shear thinning effect and higher elasticity compared to simple blends.     

PPO-g-MA对PPO/PA66共混物的原位增容作用

用傅里叶变换红外光谱证明了聚(2,6-二甲基-1,4-苯醚)(PPO)与马来酸酐(MA)在过氧化二异丙苯的作用下,采用熔融挤出法生成了PPO-g-MA。通过透射电子显微镜、扫描电子显微镜、Instron毛细管流变仪、力学性能试验机和Molau实验分别对不同PPO-g-MA用量的PPO/聚酰胺66(PA66)共混物的亚微相态、流变行为、力学性能进行了考察,结果表明,PPO-g-MA对PPO/PA66共混物起到了原位增容作用。     

Cure characteristics,morphology, mechanical properties,and aging characteristics of silicone rubber/ethylene vinyl acetate blends

Silicone rubber/ethylene vinyl acetate (SR/EVA) rubber mixes with different ratios were prepared by using dicumyl peroxide (DCP) and benzoyl peroxide (BP) as curing agents. The vulcanization characteristics such as cure kinetics, activation energy, and cure rate of the blends were analyzed. The effects of blend ratio and curing agents on the mechanical properties such as stress–strain behavior, tensile strength, elongation at break, tear strength, relative volume loss, hardness, flex crack resistance, and density of the cured blends have been investigated. Almost all the mechanical properties have been found to be increased with increase in EVA content in the blends particularly in DCP‐cured systems. The increment in mechanical properties of the blends with higher EVA content has been explained in terms of the morphology of the blends, attested by scanning electron micrographs. Attempts have been made to compare the experimental results, from the evaluation of mechanical properties, with relevant theoretical models. The aging characteristics of the cured blends were also investigated and found that both the DCP‐ and BP‐cured blends have excellent water and thermal resistance. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1069–1082, 2006     

Effects of the shapes and addition amounts of crosslinking reagents on the properties of poly-3-hydroxybutyrate/poly(caprolactone) blends

The effects of the shapes and addition amount of crosslinking reagents on the expression mechanisms of polymer properties of poly(3-hydroxybutyrate) (PHB) and poly(caprolactone) (PCL) blends are investigated. A static tensile test is carried out on 60%PHB/40%PCL blends by adding liquid and solid crosslinking reagents, showing that the Young's modulus of the blends decrease with increasing effective peroxide value of the crosslinking reagent. In addition, the elasticity of the blends increases only when the liquid crosslinker is added, even though T₁H analysis and scanning electron microscopy observation reveal that both crosslinking reagents improve the miscibility of the blend. Furthermore, the ¹H and ¹³C PST-MAS NMR spectra related to the molecular motions of polymer main chains in the blends increase with increasing effective peroxide value of the crosslinking reagents. However, the local molecular motions of substituents in the blends matched with the T₁C values reveal an opposite trend between the rigid PHB and flexible PCL with the addition of the solid crosslinker. The solid-state NMR spectral and relaxation time analyses suggest the possibility of the polymer chain scission as a side reaction, as well as the occurrence of intra-domain crosslinking, both of which reduce the toughness of the blends containing the solid crosslinker.