Natural weathering test for films of various formulations of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE)

Natural (outdoor) weathering test was performed to investigate the UV stability of thin films (0.06 mm) of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). The PE films were prepared from various formulations of LLDPE and LDPE resins. Some of these films contained a single high molecular mass HALS only, along with a primary antioxidant (i.e. Irganox 1010) and a secondary antioxidant (i.e. Irgafos 168 or Alkanox TNPP), while others contained HALS and UVA (i.e. Chimassorb 81 or Tinuvin P or Tinuvin 326) along with these antioxidants. The HALS used was either an oligomeric or a synergistic mixture of a high molecular mass (HMM) hindered amine stabilizer and co-additives. The UV stability was investigated by exposing the prepared films at 45° towards south in the direct sunshine up to 365 days. Fifty percent of tensile strength retention was determined for all these exposed films and it was found that the films containing a single HALS gained improved UV stability by about two to 12 fold over the pure films. On the other hand, films that contained a combination of HALS and UVA obtained further improved UV stability over the films containing a single HALS (both have antioxidants). Films containing a single HALS reached 50% TS retention within 205 days, whereas, films containing a combination of HALS and UVA reached 50% TS retention within 590 days, which is about three times further improvement in UV stability.     

Studies on radiation grafting of methyl methacrylate onto natural rubber for improving modulus of latex film

Methyl methacrylate (MMA) can be grafted onto natural rubber (NR) in latex by gamma irradiation for improving the mechanical properties of the dry films. Physical blending of MMA-grafted NR latex with radiation vulcanized natural rubber latex (RVNRL) or simultaneous radiation grafting and crosslinking are found to be useful techniques for improving the properties of latex films. Moduli of the films are improved with increasing MMA content; however, tensile strength is reduced. High modulus without much reduction in tensile strength can be achieved if the MMA content is 50–60 parts per hundred rubber.     

Abiotic and biotic degradation of oxo-biodegradable polyethylenes

Conventional polymeric materials accumulate in the environment due to their low biodegradability. However, an increase in the biodegradation rate of these polymers may be obtained with the addition of pro-degrading substances. This study aimed to evaluate abiotic and biotic degradation of polyethylenes (PEs) using plastic bags of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) formulated with pro-oxidant additives as test materials. These packaging materials were exposed to natural weathering and periodically analyzed with respect to changes in mechanical and structural properties. After a year of exposure, residue samples of the bags were incubated in substrates (compost of urban solid waste, perlite and soil) at 58 °C and at 50% humidity. The biodegradation of the materials was estimated by their mineralization to CO₂. The molar mass of the pro-oxidant-activated PE decreased and oxygen incorporation into the chains increased significantly during natural weathering. These samples showed a mineralization level of 12.4% after three months of incubation with compost. Higher extents of mineralization were obtained for saturated humidity than for natural humidity. The growth of fungi of the genera Aspergillus and Penicillium was observed on PE films containing pro-oxidant additives exposed to natural weathering for one year or longer. Conventional PE films exposed to natural weathering showed small biodegradation.     

Migration behaviour and distribution profiles of a bifunctional additive in two polymer matrices

A bifunctional additive (an antioxidant with an electron acceptor group) has been incorporated into two polymer matrices and the migration tendency has been studied under various conditions. The most favourable results were obtained for the new additive 3-(3,5-di-tert.-butyl-4 hydroxyphenyl)propyl 2,4,6-trinitrophenyl ether (TNPP). After storage for 10 days at 40°, TNPP migrated from high density polyethylene (HDPE) into test fat (HB 307), heptane and water-ethanol (90:10, v/v) to the extents of 14, 56 and 0.4% respectively, whereas butylated hydroxytoluene (BHT) migrated in the same systems to 32, 100 and 1.8%. Reduction of the TNPP migration in HDPE is directly related to the molecular volume of the bifunctional additive; its increased retention in an electron-donating polymer matrix is attributed to charge-transfer complex formation. A simple sectioning technique is described to establish the distribution profile of the remaining additive in the polymer after contact with various extracting test liquids.     

Investigation of polymer degradation by addition of magnesium

The effect of alkali metal magnesium on polymer degradation of physico-mechanical properties of radiation-vulcanized natural rubber latex (RVNRL) films was investigated. RVNRL films were prepared by the addition of Mg of different concentrations (0–30 ppm) to natural rubber latex and irradiation with various radiation doses (0–20 kGy). The radiation doses were optimized (12 kGy), and the adverse effect of Mg was studied against a reference film prepared without metal. Tensile strength, tear strength, and cross-linking density of the irradiated rubber films were decreased with increasing metal ion concentrations and decreasing radiation doses. The mechanical properties of the films were reduced by nearly 10% for 30 ppm Mg ions and at the optimum dose. In contrast, elongation at break, permanent set, and swelling ratio of the films were increased at the same conditions. The maximum tensile and tear strengths of irradiated rubber films without additive were 29.33 MPa and 47.95 N/mm, respectively, at a radiation dose of 12 kGy, and these values were about six times higher than those of blank samples. With the addition of Mg, the corresponding values decrease continuously, and the minimum values were found to be 26.35 MPa and 42.675 N/mm, respectively. The effect of divalent alkali metal on polymer chain scission can be explained by the classical electron concept reported in this article.     

ROLE OF SYNTHETIC ANTIOXIDANTS ON THE AGING PROPERTY OF ELECTRON BEAM IRRADIATED NATURAL RUBBER

The aging property of radiation vulcanized natural rubber was studied using various kinds of antioxidants. Aging test was done at 100℃ for various lengths of time. It was found that some antioxidants are excellent in preventing the oxidative degradation of the irradiated rubber. DAH (2,5-di-tert-amylhydroquinone) CBP (2,2‘-dihydroxy-3,3‘-di(-methylcyclohexyl)-5,5‘-dimethyl diphenyl methane) P16 (tris(2,4-di-tert-butylphenyl)phosphate) in a proportion of (1:0.5:0.5) was found to be the best combination to achieve 100% retention of tensile strength.     

The Effect of 3-aminopropyltrimethyoxysilane (AMEO) as a Coupling Agent on Curing and Mechanical Properties of Natural Rubber/Palm Kernel Shell Powder Composites

This research is conducted using palm kernel shell powder (PKS) as filler in natural rubber The effect of 3-aminopropyltrimethoxysilane as coupling agent on composites were studied at different palm kernel shell loading i.e, 0 5, 10, 15 and 20 phr The palm kernel shell was crushed and sieved to an average particle size of 5.53 μm The palm kernel shell filled natural rubber composites were prepared using laboratory size two roll mill The curing characteristics such as scorch time, cure time and maximum torque were obtained from rheometer The palm kernel shell powder filled natural rubber composites were cured at 150^oC using hot press according to their cure time Curing characteristics, tensile properties, rubber-filler interaction and morphological properties of palm kernel shell powder filled natural rubber were studied Scorch time and cure time show reduction but tensile strength, elongation at break, modulus at 100% (M100) and modulus at 300% (M300) increased with the presence of 3-aminopropyltrimethyloxysilane Rubber-filler interaction studies showed that rubber filler interaction in natural rubber filled with palm kernel shell powder improved with incorporation of 3-aminopropyltrimethyoxysilane.     

天然橡胶/聚乙烯共混体相容性的研究

本工作首先对橡胶/聚乙烯共混体系的相容性进行了计算,推测聚乙烯的非晶部分和橡胶间有一定的互容性,提出了橡胶和聚乙烯相互作用模型。然后用动态力学方法、有效网链密度测定、密度测定和广角X-射线衍射方法对天然橡胶分别未交联和交联的天然橡胶(NR)/低密度聚乙烯(LDPE)共混体系的相容性进行了验证。实验结果表明,LDPE非晶部分和NR之间存在一定的相互渗透。     

Properties of Natural Rubber/Recycled Chloroprene Rubber Blend: Effects of Blend Ratio and Matrix

The present study investigated the effects of two types of natural rubber and different blend ratios on the cure, tensile properties and morphology of natural rubber/recycled chloroprene rubber blends. The blends of natural rubber/recycled chloroprene rubber were prepared by using laboratory two-roll mill. The result showed that the cure time prolonged with the addition of recycled chloroprene rubber (rCR). Comparability, natural rubber/recycled chloroprene rubber (SMR L/rCR) blendcured rapidly than epoxidized natural rubber/recycled chloroprene rubber (ENR 50/rCR) blend. The addition of rCRalso caused a decrement in the tensile strength and elongation at break for both rubber blends. The SMR L/rCR blendsshowed higher tensile strength and elongation at break compared to those of ENR 50/rCR blends at any blend ratios.     

Curing and Physical Properties of Natural Rubber/Wood Flour Composites

Natural rubber based composites were prepared by incorporating Wood flour of two different particle size ranges (250–300 µm) and (300–425 µm) and concentrations (15 and 30 phr) into the matrix, using a Banbury® internal mixer according to a base formulation. Curing characteristics of the samples were studied. Influence of particle size and loading of filler on the properties of the composites was analyzed. Results obtained show that the addition of wood flour to natural rubber increased scorch time and curing time and caused improvement in modulus at 300% strain and in tear properties. However, it decreased tensile strength and elongation at break. The particle size range of 300–425 µm was found to offer the best overall balance of mechanical and dynamic properties (tan δ and viscous torque). Swelling behavior of the composites in toluene was also analyzed in order to determine the rubber volume fraction and crosslinking density. Composites with the bigger particle size wood flour were found to have greater crosslinking density than the ones with smaller particle size, fact that could possibly indicate a better rubber-filler interaction in the former. Major percentage of filler increased slightly this interaction. Water absorption behavior of the composites with wood flour reached a maximum of 12% w/w when 30 phr of filler were incorporated; nonetheless, particle size did not affect this property. The ageing study in presence of air at 70 °C revealed that natural rubber composites with wood flour maintained the same classification cell with temperature as the pure rubber. A compound with 30 phr of carbon black was prepared for comparative purposes. Results obtained were as expected. Scorch time decreased and higher values of modulus at 300% strain and tensile strength were achieved, due to strongest interaction between filler and elastomer.     

Effect of Manganese on Radiation Vulcanization of Natural Rubber

Manganese was added as a promoter to investigate physico-mechanical properties of radiation-vulcanized natural rubber latex (RVNRL) films. RVNRL films were prepared by the addition of Mn with the concentration range 0–30 ppm to natural rubber latex and irradiated with various radiation doses (0–20 kGy). Tensile strength, tear strength, and cross-linking density of the irradiated rubber films increased with increasing the concentration of Mn ions as well as radiation doses. In contrast, elongation at break, permanent set, and swelling ratio of the films were decreased under the same conditions. The concentration of Mn ions and radiation doses were optimized and found to be 20 ppm and 12 kGy, respectively. The maximum tensile and tear strengths of irradiated rubber films were observed as 29.12 MPa and 44.78 N/mm, respectively at the optimum conditions. The mechanical properties of the films increased markedly with the addition of Mn until they attained the highest values of 33.88 MPa and 54.77 N/mm, respectively. These enhancements, which reached approximately 20% at the most favorable conditions, can be explained by the effect of transition metals in view of Fajan’s rules regarding the covalent character of ionic bonds and suggest that the higher the difference in charges between cation and anion, the higher the ability to form distortion or polarization of ions.     

天然微晶纤维素晶须补强天然橡胶的研究

采用硫酸酸解天然微晶纤维素(microcrystalline cellulose,简称MCC)制备纳米微晶纤维素晶须(cellulosewhisker,简称CW),加入天然橡胶胶乳共沉后混炼硫化.结果表明,CW对天然橡胶具有明显的补强作用,经间苯二酚(R)与六亚甲基四胺(H)改性后,NR/RH-CW复合材料的模量、断裂伸长率和撕裂强度都进一步改善.热空气(100℃,72 h)老化后,NR/RH-CW复合材料的力学性能明显优于纯NR,其拉伸强度由28.54 MPa下降至21.78 MPa,变化率缩小至23.7%;断裂伸长率由594%下降至493%,变化率缩小至17.0%,而纯NR的拉伸强度由22.0 MPa下降至2.4 MPa,变化率为89.1%;断裂伸长率由579%下降至168%,变化率为71.0%.扫描电镜分析表明,RH-CW与NR基体的界面相容性较CW改善.热重分析表明,CW的加入使NR的5%失重温度降低,但残重增加,微分曲线在520℃处出现了一个小峰,RH-CW的加入,使该峰变大,残重进一步增加.     

Properties and recyclability of thermoplastic elastomer prepared from natural rubber powder (NRP) and high density polyethylene (HDPE)

Preparation of thermoplastic natural rubber (TPNR) was carried out by blending high density polyethylene (HDPE) with natural rubber powder (NRP) obtained from spray drying of pre-vulcanized natural rubber latex. The blend ratio of NRP/HDPE was varied and the properties and recyclability of the TPNRs were investigated. The results reveal that, due to flow restriction of the crosslinked NRP, viscosity of the TPNR increases continuously with increasing NRP content. As expected, when NRP content is increased, properties of the TPNR are more rubber-like, as clearly observed from the stress–strain curve characteristics, the reductions in modulus and hardness and, most importantly, the significant improvement of permanent set. Although phase size of the dispersed NRP is relatively large, the tensile strength tends to increase gradually with increasing NRP content. The phenomenon of strain-induced crystallization is proposed to explain the results. It is also found that recycling has a noticeably detrimental influence on most properties of the TPNRs such as tensile strength, tear strength, hardness and tension set. This is thought to be a consequence of thermal degradation of the NRP during the recycling process.     

PREPARATION OF HIGH-TEMPERATURE VULCANIZED SILICONE RUBBER OF EXCELLENT MECHANICAL AND OPTICAL PROPERTIES USING HYDROPHOBIC NANO SILICA SOL AS REINFORCEMENT

Hydrophobic nano silica sol(HNSS)was incorporated into polyvinylmethylsiloxane to prepare reinforced high- temperature vulcanized(HTV)silicone rubber.HTV silicone rubber filled with 40 phr HNSS showed excellent mechanical and optical properties:the tensile strength reached 11.7 MPa and the optical transmittance was higher than 90%.Possible reasons for reinforcement and transparency were discussed on the basis of the bound rubber percentage,total crosslink density,and SEM analysis.Our work suggests that H...     

剥离型硅橡胶/黏土纳米复合材料研究

利用层状硅酸盐制备有机 无机纳米复合材料是当前人们研究的热点[1,2 ] ,这类材料具有较常规聚合物 无机填料复合材料无法比拟的优点 ,可以明显改善高分子材料的物理机械性能、热稳定性、气体阻隔性、阻燃性、导电性、光学性等 .一般来说 ,聚合物 层状硅酸盐 (Ｐｏｌｙｍｅｒｌａｙｅｒｅｄｓｉｌｉｃａｔｅ ,ＰＬＳ)纳米复合材料可分为插层型和剥离型两种类型 .插层型纳米复合材料即聚合物插入到硅酸盐层中 ,硅酸盐在近程仍保持原有的有序晶体结构 ,在远程则是无序的 .对弹性体而言 ,硅酸盐含量在插层型杂化材料中的含量比较高 ,力学性能…     

Investigation on the effect of cellulosic nanoparticles’ morphology on the properties of natural rubber based nanocomposites

Cellulose whiskers and microfibrillated cellulose (MFC) were extracted from the rachis of date palm tree and characterized. These cellulosic nanoparticles were used as reinforcing phase to prepare nanocomposite films using latex of natural rubber as matrix. These films were obtained by the casting/evaporation method. The properties of the ensuing nanocomposite films were investigated using differential scanning calorimetry, toluene and water uptake experiments, dynamic mechanical analysis and tensile tests. The stiffness of the natural rubber was significantly increased above its glass-rubber transition temperature upon nanoparticles addition. The reinforcing effect was shown to be higher for nanocomposites with MFC compared to whiskers. It was ascribed to the higher aspect ratio and possibility of entanglements of the former. The presence of residual lignin, extractive substances and fatty acids at the surface of MFC was also suggested to promote higher adhesion level with the polymeric matrix.     

Protein-free natural rubber

Some properties of protein-free natural rubber were investigated by measurements of both water uptake and stress versus strain. The protein-free natural rubber was prepared in latex stage by the novel procedure to remove all proteins from natural rubber with urea and a polar organic solvent in the presence of surfactant, which had been developed in our recent work. First, the condition for the removal of the proteins was investigated in terms of affinity of the polar organic solvents, concentration of the solvents, type of surfactant, and repeating times for washing latex with a centrifuge. Acetone and anionic surfactant were found to be effective for the removal of the proteins. Under an optimum condition, total nitrogen content and amount of extractable proteins of deproteinized natural rubber were 0.000 w/w% and 0.00 μg/ml, respectively. The removal of the proteins from natural rubber was confirmed through Fourier transform infrared (FT-IR) spectroscopy. Water uptake, hydration, and tensile strength of the rubbers were measured by water swelling method, FT-IR spectroscopy, and measurement of stress versus strain, respectively. The water uptake and the hydration were dependent upon the content of the proteins. The tensile strength of the rubbers, which were prepared to be as-cast films without crosslinking, decreased after removal of the all proteins.     

Mechanical properties of radiation-induced graft copolymers of styrene to polyethylene

Measurements were made of the tensile properties polyethylene-styrene grafts prepared by irradiating polyethylene films in liquid styrene. The films contained true graft and occluded styrene homopolymer. It was shown that yield strength, tensile strength, and initial modulus of elasticity increase while elongation decreases with increasing polystyrene content. The tensile strength and elongation were reduced when the grafted film was soaked in benzene more than 15 hr. The film prepared by a post-irradiation graft gave higher tensile strength and elongation than those of grafts formed by simultaneous irradiation of the film and the monomer. These results indicate that radiation-induced grafting makes the system of polyethylene and polystyrene compatible and potentially useful, provided the samples are not subjected to drastic solvent extraction procedures for the removal of homopolymer.     

Contributions to the Characterization of Chlorinated Polyisoprene Surfaces

Summary: The present work is focused on the characterization of the surface properties and the mechanical properties of chlorinated polyisoprene films. Cross-linked polyisoprene films were treated with acidified hypochlorite solution and the influence of the chlorination time on the surface properties was determined by spectroscopic techniques including FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface morphology was investigated by scanning electron microscopy (SEM), optical microscopy and contact angle measurements. In addition, the effect of the chlorination time on the tensile strength and ageing stability of natural rubber latex gloves was investigated.     

Radiation vulcanization of NR/SBR composite enhanced with different polyfunctional monomers

The effect of different polyfunctional monomers (PFMs) as enhancing agents on the properties of natural rubber/styrene-butadiene rubber blend reinforced with 40 (phr) part per hundred part of rubber, by weight of HAF carbon black and vulcanized with gamma irradiation was investigated. The coagents N,N’ methylene diacrylamide (MDA), trimethylol propane-trimethacrylate (TMPTMA) and trimethylol-methane tetraacrylate (TMMTA) were used at a constant content of 5 phr. The physico-chemical properties such as tensile strength, tensile modulus at 100 % elongation, elongation at break, gel fraction and swelling number were studied. The results indicated that the properties are greatly improved by PFMs at lower doses. TMMTA as coagent is more effective than TMPTMA and MDA.