纳米氧化锌对天然胶乳膜干燥及硫化性能影响研究

采用失重法和溶胀法研究了普通氧化锌和纳米氧化锌活化的天然胶乳膜的干燥动力学,以及干燥过程中胶乳膜交联密度变化.结果表明:天然胶乳厚胶膜在成膜后仍含有大量水分并且去除困难.纳米氧化锌活化胶膜的干燥速率明显高于普通氧化锌胶膜.干燥温度对干燥过程影响显著,干燥时间随干燥温度升高明显降低.随着干燥的进行,2种氧化锌活化的胶乳膜的交联密度均迅速上升,在相同条件下,纳米氧化锌活化胶乳膜交联密度均比普通氧化锌的大.纳米氧化锌对天然胶乳膜的干燥及硫化过程均有促进作用.     

Composite natural rubber based latex particles: a novel approach

The oil resistance of natural rubber (NR) film could be effectively improved by using the heterocoagulation of large NR particle with small polychloroprene (CR) particles. In the preparation of NR/CR composite particle with a core-shell structure, a nonionic surfactant whose molecule bears poly(ethylene oxide) (PEO) was adsorbed on CR particles and allowed to form complexes between PEO and indigenous surfactant (protein-lipid) on the NR particle surface. Composite latex particle obtained was characterised by particle size, zeta potential and glass transition temperature measurements and the data indicated the presence of CR on the outer layer of composite particle. Better oil resistance of film casted from heterocoagulated latex when compared to that of NR film confirmed the NR/CR core-shell structure. The epoxidised natural rubber (ENR), crosslinked ENR and/or skim latex particles were investigated in order to replace the use of CR in the heterocoagulation process.     

用作载重子午线轮胎胎面胶的炭黑填充粉末NR结构与性能研究

以天然胶乳和炭黑N234为原料,采用凝聚共沉法制备炭黑填充型粉末NR[P(NR/CB)],研究炭黑用量和不同配方对胶料硫化特性、物理性能、交联密度、微观结构、Payne效应及动态力学性能的影响,并与采用传统机械混炼法制备的炭黑/NR(CB/NR)进行对比.结果表明,与CB/NR硫化胶相比,P(NR/CB)硫化胶具有较高的拉伸强度、撕裂强度、回弹值和抗湿滑性能以及较低的滚动阻力,耐屈挠性能和耐磨性能大致相当,而动态压缩生热和压缩永久变形则降低了近50%.     

Carbon black filled powdered natural rubber: Preparation,particle size distribution,mechanical properties,and structures

Carbon black (HAF) filled powdered natural rubber (P(NR/HAF)) was prepared and the particle size distribution, mechanical properties, and micromorphology of P(NR/HAF) were studied. A carbon black–rubber latex coagulation method was developed for preparing carbon black filled free‐flowing, noncontact staining NR powders with particle diameter less than 0.9 mm. A powdering mechanism model was put forward to describe the powdering process, which shows that the key technical points consist in the surfactant with good emulsification properties and the polymer coating resin with good film forming properties. SEM analysis shows that carbon black and rubber matrix have formed a macroscopic homogenization in the P(NR/HAF) particles without contact staining, and carbon black particles are well dispersed in rubber matrix with diameter of about 50–150 nm. P(NR/HAF) vulcanizate showed better mechanical properties than bale natural rubber/carbon black blends (NR/HAF) and simple NR latex/carbon black blends (NRL/HAF), which depends primarily upon the absence of free carbon black, the fine dispersion of filler on the rubber matrix, and the better interaction between carbon black and rubber matrix due to the proper preparation condition of noncontact staining carbon black filled powdered NR. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1763–1774, 2006     

Acetoacetoxy functionalized natural rubber latex capable of forming cross-linkable film under ambient conditions

This work demonstrates that natural rubber (NR) latex particles containing acetoacetoxy (AcAc) groups are able to undergo cross-linking upon film formation at ambient temperature by reaction with glutaraldehyde (GTA). Natural rubber latex grafted with poly(acetoacetoxyethyl methacrylate) (NR-g-PAAEM) was synthesized by seeded emulsion polymerization, using benzoyl peroxide (BPO) as an initiator in free radical polymerization. The degree of grafting of PAAEM in the graft copolymers was evaluated by ¹H NMR technique. Transmission electron microscope (TEM) was used for investigation the particle morphology of the grafted NR latex. Since the AcAc groups are intentionally attached to the NR particles providing sites of cross-linking at ambient temperature, the cross-linking ability of these sites by reaction with GTA was then investigated. The results revealed that the latex film of NR-g-PAAEM with the addition of GTA had a much higher tensile strength in comparison with the film without GTA. The surface morphology of the NR-g-PAAEM latex film formed in the absence and presence of the GTA cross-linker was also investigated using atomic force microscopy (AFM). By GTA addition into the NR-g-PAAEM latex before film formation, an increase in the root-mean-square (RMS) roughness of the surface of the latex film was observed. Moreover, it was also observed that the NR-g-PAAEM films with the addition of GTA had higher activation energy for thermal degradation than that without the cross-linker. This confirms that the cross-linking reaction took place in the NR-g-PAAEM latex film as a result of its reaction with the GTA.     

Effect of NaOH and Si69 treatments on the properties of fly ash/natural rubber composites*

Natural silica in fly ash (FA) particles of 30 and 60 phr were incorporated as reinforcing filler in natural rubber (NR) compounds. Improvements of cure characteristics and mechanical properties of the FA/NR composites were expected by surface treatment of the FA particles, this being carried out using various contents of bis‐(3‐triethoxysilylpropyl) tetrasulfane (Si69), as a chemical silane coupling agent, and sodium hydroxide (NaOH) solution. The results suggested that the Si69 coupling agent was a satisfactory property promoter in the FA/NR composites through C S bonding with rubber molecules and siloxane linkages with FA particles. Using NaOH solution did not improve the mechanical properties of the composites. The mechanical properties of the FA/NR composites appeared to increase at low Si69 concentrations of 2.0–4.0 wt%, but decreased at high Si69 loadings of 6.0–8.0 wt%. The decrease in mechanical properties resulted from a reduction of crosslink density and a formation of flexible polysiloxane from the self‐condensation reaction of the Si69. The presence of Si69 was observed to interfere with the sulphur crosslink formation. No synergetic effect on the properties of the rubber composites was observed when using a mixture of NaOH and Si69. This article recommends concentrations of 2.0–4.0 wt% Si69 to be introduced into the FA/NR composites to achieve the optimum properties. POLYM. COMPOS., 27:30–40, 2006. © 2005 Society of Plastics Engineers     

Pre‐Vulcanization of Large and Small Natural Rubber Latex Particles: Film‐Forming Behavior and Mechanical Properties

The pre‐vulcanized large rubber particle (LRP) and small rubber particle (SRP) latices are independently prepared to investigate their film‐forming process and mechanical properties after being cast into films. The surface morphologies and roughness of both LRP and SRP films are found to be dependent on crosslink densities. The networks inside each rubber particle (RP) restrict particle deformation resulting in residual contour of RP within the film surface. For highly crosslinked RP, the collapse of the top surface of the RPs in the LRP films appears to create many “crater‐like” structures within the film surfaces, while they present only protruding particles within the SRP and blend films. This seems to indicate that LRPs are easier to coalesce and form film than SRPs. Additionally, dynamic and mechanical properties and strain‐induced crystallization (SIC) behaviors of the latex films, are effectively enhanced after pre‐vulcanization. The pre‐vulcanized LRP films perform better tensile properties and SIC than the SRP can.     

Characteristics of the photochemical prevulcanization in a falling film photoreactor

The photochemical prevulcanization of natural rubber (NR) latex via the thiol‐ene reaction is a new approach aiming at the replacement of noxious processing agents used in conventional sulfur vulcanization processes (e.g., accelerators) together with cost saving options. The crosslinking reaction involves the excitation of a selected photoinitiator with ultraviolet (UV) light which is followed by the formation of thioether links due to the thiol‐ene addition reaction. The photochemical process is carried out in a falling film photoreactor which provides not only a continuous prevulcanization process but also exhibits a technology which is already commercially well established. The main advantage of the falling film process lies in the short prevulcanization time and the mild reaction temperature. Following the idea of the manufacture of low‐allergenic surgical gloves made from NR latex without compromising on the glove quality by means of physical performance, crucial process parameters of the falling film process have been determined and characterized in this study. Surgical gloves were made from the photocured NR latex which was prevulcanized using selected process conditions. The physical properties including tensile strength, elongation, modulus, and crosslink density were examined together with the aging stability and the stability against high‐energy radiation (sterilization with gamma rays). It was found that the UV light intensity, the number of illumination cycles, the choice of photoinitiator, and the thiol crosslinker play an important part in the glove quality. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Silica nanoparticles reinforced natural rubber latex composites: The effects of silica dimension and polydispersity on performance

The nano-size autonomous monodisperse silica (AS) particles were prepared by hydrolysis and condensation of tetraethoxysilane using l -lysine as catalyst. The silica/natural rubber (NR) masterbatches were then produced via latex compounding, in which NR latex was mixed with the above AS dispersion. The commercial precipitated silica (PS) was introduced as a control. The effects of both AS and PS particles on the interfacial and mechanical properties of composites were systematically examined. It was found that the AS formed bead-like morphology wherein the clear particle edges can be distinguished in rubber matrix. Compared with PS/NR, the AS/NR composites were proved to possess more bound rubber and weaker filler–filler interaction resulting in higher tensile strength, abrasive resistance, and resilience. Meanwhile, the efficiency of premodified AS and PS surfaces using bis-(3-triethoxysilylpropyl) tetrasulfide on reinforcing the properties of silica/NR composites was studied. The results presented that the overall properties of modified silica/NR vulcanizates were improved significantly. In special, the values of heating building-up and compression set showed an evident decline which was of great significance for tire tread or other rubber products. For the dynamic properties, the magic angle spinning/NR composites had lower rolling resistance. In short, AS may be applied as an ideal substitution of PS in rubber. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47449.     

三种微生物脱硫废乳胶及其填充天然橡胶的力学性能比较

利用三种微生物鞘氨醇单胞菌、脂环酸芽孢杆菌和酵母菌对废乳胶(WLR)进行了脱硫再生,考察了脱硫过程中微生物的生长情况以及脱硫前后WLR溶胀和交联密度的变化,并将WLR和脱硫WLR(DWLR)以不同份数填充到天然橡胶(NR)中,对比了DWLR/NR硫化胶和WLR/NR硫化胶的力学性能和交联密度。结果表明,利用鞘氨醇单胞菌脱硫的WLR溶胀值较高,交联密度较低。随着乳胶用量的增加,填充NR硫化胶的拉伸强度和交联密度逐渐降低,扯断生长率逐渐增加。DWLR/NR硫化胶的力学性能明显优于WLR/NR硫化胶,且鞘氨醇单胞菌脱硫的DWLR/NR的力学性能明显优于其它两种微生物脱硫的DWLR/NR硫化胶。     

Layer-by-layer thin films of polyaniline alternated with natural rubber and their potential application as a chemical sensor

Self-assembled films of polyaniline (PAni) alternated with natural rubber (NR) were successfully produced by layer-by-layer self-assembly technique (LbL), by using the latex of natural rubber obtained from the Hevea-brasiliensis tree. The centrifuged NR latex was used without any previous treatment. The influence of pH on the adsorption kinetics and film growth was evaluated. The films presented a typical linear growth, showing a constant adsorption of material in each deposition step. The FTIR spectroscopy study confirmed the presence of rubber chains (cis-1,4-poly-isoprene) on the LbL films. The morphological characterizations showed great roughness and a spherical shape of the NR particles as a predominant characteristic on the film’s surface. Finally, the potential use of the films as a chemical sensor was identified in our tests.     

氯化石蜡共混改性天然胶乳的研究

分别采用氯化石蜡、氯化石蜡／Sb2O3共混改性天然胶乳．考察了改性胶乳硫化胶膜的力学性能及阻燃性能．并进行了TG·DTG和DSC分析。结果表明：改性胶乳的阻燃效果比未改性天然胶乳的高．且氯化石蜡／Sb2O3共混改性天然胶乳可产生协同阻燃效果；随Sb2O3用量的增加．硫化胶膜撕裂强度增加．而拉伸强度下降。氯化石蜡／Sb2O3改性胶乳的热降解过程为二步反应．且起始热降解温度比天然胶乳的低．玻璃化转变温度提高。     

The effect of thiol and ene structures on thiol-ene networks: Photopolymerization, physical, mechanical and optical properties

The photopolymerization of four different types of ene monomers with both primary and secondary multifunctional thiols has been evaluated. To understand the effect of ene monomer structures on polymer properties, a comprehensive investigation of the basic physical, mechanical and optical properties was conducted for the secondary and primary thiol-ene networks. The results indicate that ene structure and functionality can significantly affect the rigidity and the physical and mechanical properties of the thiol-ene networks. The heat capacity in the rubber state correlates with the network crosslink density and flexibility of the ene component. Networks formed from the secondary thiol-ene systems are basically equivalent to those made from primary thiol-enes with respect to physical, mechanical and optical properties. The secondary thiol monomer samples evaluated were found to have exceptional storage stability and relatively low odor.     

Effects of quasi‐nanogel particles on the rheological and mechanical properties of natural rubber: A new insight

The influence of sulfur‐crosslinked, quasi‐nanosized gels on the rheological and mechanical properties of raw natural rubber (NR) was investigated. Latex gels with different crosslink densities were prepared through the variation of the sulfur‐to‐accelerator ratio. These gels were characterized by dynamic light scattering, solvent swelling, and mechanical properties. The gels were mixed with raw NR latex at concentrations of 2, 4, 8, and 16 phr, and their effect on the rheological properties of NR was studied by Monsanto processability tester. The presence of gel in raw NR reduced the apparent shear viscosity and die swell considerably. Initially, the viscosity decreased up to a 8 phr gel loading and then increased with an increase in the gel loading. However, the change in the viscosity was related to the crosslink density of the gels. A new empirical equation relating the viscosity, volume fraction of the gels, and crosslink density was proposed. The die swell of gel‐filled raw NR was at least 10% lower than that of unfilled raw NR and decreased with an increase in the gel loading. The effect of the gels on the die swell properties was explained through the calculation of the principal normal stress difference of gel‐filled NR systems. Scanning electron photomicrographs of the extrudates revealed much better surface smoothness for the gel‐filled virgin rubber systems than for the unfilled rubber. The addition of the gels to raw NR increased the modulus and tensile strength, whereas the elongation at break decreased. The effect of the gels on the dynamic mechanical properties of NR was also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Physicochemical and antimicrobial properties of natural rubber latex films in the presence of vegetable oil microemulsions

A series of vegetable oil microemulsions are formulated and incorporated into NR latex to study the potent antimicrobial activity of vegetable oil‐plasticized NR latex film against the adherent bacteria on the treated film. The particle size of latex incorporated with 2.50 phr of oil has attained up to 424 nm after incubated at 35 ± 2 °C for 24 h. The tensile stress of all NR latex films are relatively low, ranged 0.289 to 0.511 MPa. All emulsions are found compatible with NR and the low contact angles (<90°) corresponded to no oil blooming onto the surfaces of NR latex films. The crosslink densities are in good correlation with tensile strengths. The potent antimicrobial properties of the NR latex films are investigated from the viability assessment of the adherent tested Escherichia coli ATCC 25922 (E. coli ATCC 25922) and Staphylococcus aureus ATCC 25923 (S. aureus ATCC 25923). Results shows that NR latex film incorporated with palm kernel oil/soybean oil blend, NR‐E(P/S = 7/3), has significantly killed the adherent S. aureus with 92.5% reduction but showed no significant log reduction in E. coli. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44788.     

Mechanical properties of siliceous earth/natural rubber composites

Siliceous earth (SE), which has a special morphology and structure, was selected as filler of natural rubber (NR) and mechanical properties of compounds were analyzed. Two processes were employed to prepare SE/NR compounds described as mechanical mixing method and latex method, respectively. Cure characteristics, mechanical properties of the vulcanizates prepared from the masterbatches were compared with those prepared by mechanical mixing method. X‐ray diffraction results of NR/SE vulcanizations indicated that mechanical mixing above the latex process facilitated the intercalation of NR into the galleries of SE. The results of mechanical properties show that SE has good reinforcing properties on NR both by latex or mechanical mixing process. By comparison, H samples show slightly higher crosslink density, tensile strength, 300% modulus, and lower elongation at break than M sample in same loading. But in the aspect of dynamic properties there exist obviously difference between latex and mechanical mixing process. Rubber processing analyzer (RPA) results showed that uncured M samples showed obviously higher storage modulus than that of H samples. The heat build‐up of M30 is much lower than that of H30. These behaviors indicated better dynamitic properties when the masterbatches prepared by the predispersing method was utilized. POLYM. ENG. SCI., 58:1043–1052, 2018. © 2017 Society of Plastics Engineers     

Rare earth compounds modified carbon black filled powdered natural rubber: Preparation,morphology and properties

Ten types of rare earth (RE) compounds modified carbon black (HAF‐RE) were prepared using chemical‐deposit method, then HAF‐RE were mixed with natural rubber latex to prepare HAF‐RE filled powdered natural rubber [P(NR/HAF‐RE)] by a carbon black/rubber latex coagulation method. It is found that most of the P(NR/HAF‐RE) vulcanizates showed better mechanical properties, especially higher tensile modulus, and tensile strength, compared with none‐rare earth modified carbon black filled powdered natural rubber [P(NR/HAF)]. Dysprosium (Dy) modified carbon black (HAF‐Dy) filled powdered natural rubber [P(NR/HAF‐Dy)] was chosen for intensive investigation because of its better comprehensive mechanical properties. It is found that the adding of Dy compounds could help to get smaller particles with narrower particle size distribution, and results from the SEM analysis show that carbon black has been dispersed in rubber matrix uniformly with diameter of 50–150 nm. The TEM analysis showed that Dy compounds could obviously reduce the aggregation of primary particles of carbon black, and promote the dispersion of carbon black in P(NR/HAF‐Dy) particles. © 2008 Wiley Periodicals, Inc. JAppl Polym Sci 2008     

ENR改性陶土和填充NR硫化胶结构与性能的研究

采用环氧化天然橡胶（ENR25和ENR45）改性陶土,通过对混炼胶结合胶质量分数、硫化胶表观交联密度、补强性能和力学性能的测定,研究了ENR与陶土的相互作用,ENR的环氧化程度及ENR的用量对陶土和填充NR硫化胶结构与性能的影响。结果表明,ENR可提高陶土与NR间界面的作用强度,提高混炼胶的结合胶质量分数,增大硫化胶的表观交联密度,改善硫化胶的网络结构,提高陶土填充NR硫化胶的力学性能,其中ENR25对陶土的改性效果优于ENR45。     

Maillard reaction in natural rubber latex: Improvement of concentration process

Maillard reaction in natural rubber (NR) latex was studied by treating fresh latex with formaldehyde and glutaraldehyde. Volatile fatty acid number of the treated latex could be lower than acceptable limit (< 0.08) for more than 20 days. Attenuated total reflectance infrared spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed the occurrence of protein crosslinks in the treated latex. NR treated with glutaraldehyde has much higher nitrogen content than NR treated with formaldehyde and untreated NR, respectively. Colloidal stability of rubber particles, represented by pH, zeta potential, viscosity, and particle size distribution information, were unchanged after treating the latex with formaldehyde. Treatment of the fresh latex with glutaraldehyde 100 and 200 mmol/kg of latex led to the aggregation of rubber particles. Interestingly, the Maillard crosslinking of proteins in fresh latex could efficiently promote the transfer of rubber particles from the serum phase into the cream phase during centrifugation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45224.     

Green strength of natural rubber: The origin of the stress–strain behavior of natural rubber

The variation of the green strength of natural rubber (NR) with the preparation method of the film was studied to elucidate the origin of the stress–strain behavior characteristics of NR in connection with the structure of branch points in NR. A rubber film prepared via casting from NR latex showed the highest modulus and green strength in comparison with films prepared via casting from a toluene solution and via the hot pressing of dry rubber. The modulus and green strength of the NR latex‐casting film decreased after the hot‐press treatment of the film. On the other hand, no difference was observed for synthetic cis‐1,4‐polyisoprene rubber with the preparation method of the film or the heat treatment. This stress–strain behavior characteristics of NR can be ascribed to the changes in the branch points of the NR film with the casting method, which may result in differences in entanglement and crystallizability on stretching. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009