Creaming skim natural rubber latex for encapsulation of urea fertiliser

Abstract

Skim natural rubber latex has been characterised before crosslinking with γ-radiation. Micrographs of γ-vulcanised skim particles embedded in polystyrene revealed a semi-interpenetrating polymer network morphology of fine rubber–polystyrene particles surrounded by membrane layer. Creamed skim latex was prepared by addition of 15–45 phr sodium alginate and further used for encapsulation of urea fertiliser. Non-spherical capsules containing an homogeneous urea dispersion were obtained.     

Preparation and characterization of organoclay‐rubber nanocomposites via a new route with skim natural rubber latex

Skim natural rubber latex (SNRL) is a protein rich by‐product obtained during the centrifugal concentration of natural rubber (NR) latex. A new method to recover rubber hydrocarbon and to obtain nanocomposites with organoclay (OC) was investigated. The approach involved treatment of SNRL with alkali and surfactant, leading to creaming of skim latex and removal of clear aqueous phase before addition of OC dispersion. Clay mixed latex was then coagulated to a consolidated mass by formic acid, followed by drying and vulcanization like a conventional rubber vulcanizate. X‐ray diffraction (XRD) studies revealed that NR nanocomposites exhibited a highly intercalated structure up to a loading of 15 phr (parts per hundred rubber) of OC. Transmission electron microscopy studies showed a highly exfoliated and intercalated structure for the NR nanocomposites at loadings of 3–5 phr organically modified montmorillonite (OMMT). The presence of clay resulted in a faster onset of cure and higher rheometric torque. The rubber recovered from skim latex had a high gum strength, and a low amount of OC (5 phr) improved the modulus and tensile strength of NR. The high tensile strength was supported by the tensile fractography from scanning electron microscopy. Thermal ageing at 70°C for 6 days resulted in an improvement in the modulus of the samples; the effect was greater for unfilled NR vulcanizate. The maximum degradation temperature was found to be independent of the presence and concentration of OC. The increased restriction to swelling with the loading of OC suggested a higher level of crosslinking and reinforcement in its presence. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3277–3285, 2006     

Creaming of skim natural rubber latex with chitosan derivatives

To recover residual rubber from skim natural rubber (SNR) latex, a novel method was developed on the basis of the use of water‐soluble chitosan derivatives. An anionic chitosan derivative, N,O‐carboxymethyl chitosan (CMCh), and a cationic chitosan derivative, N‐(2‐hydroxy)propyl‐3‐trimethylammonium chitosan chloride (HTACh), were prepared. It was found that the creaming process could be achieved with both chitosan derivatives. By the addition of 7.34–10.3‐g/L CMCh, SNR latex was almost completely creamed, and no coagulation of SNR particles in the cream phase occurred. In the case of HTACh, the creaming process was achieved with a lower concentration (<3.70 g/L) than in the case of CMCh, but the size of SNR particles in the cream phase was larger. Solid‐state ¹³C‐NMR, thermogravimetric analysis, and ζ potential measurement results provided evidence that the creaming of SNR latex with CMCh and HTACh was controlled by the depletion flocculation and adsorption mechanisms, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

溴化丁基橡胶/酚醛硫化树脂复合胶乳的制备与硫化

通过溶液乳化法制备了固含量为9.3%的溴化丁基橡胶/酚醛硫化树脂复合胶乳.以海藻酸钠为膏化剂对复合胶乳进行了膏化浓缩,研究了膏化剂用量对膏化时间、胶乳固含量和胶乳粒径的影响,结果表明膏化浓缩胶乳粒径较大,膏化周期较长,一般需半个月左右才能得到实用的浓缩胶乳.采用扫描电镜观察了复合胶乳干胶膜的断面形貌,发现大粒径的膏化胶乳成膜后胶粒间可以较好地融合.通过涂布、烘干和硫化等工艺制备了厚度为0.60 mm的复合胶乳硫化膜片,并测试了硫化膜片的力学性能和H2渗透性能,结果表明硫化膜片的力学性能较好,其H2渗透率较低,为天然橡胶的9.64%、氯丁橡胶的71.3%.     

金属离子钝化剂添加工艺对胶清橡胶性能的影响研究

通过不同的添加工艺将乙二胺四乙酸二钠(EDTA-2Na)、柠檬酸钠(NaCA)、三聚磷酸钠(STPP)三种金属离子钝化剂加入胶清橡胶,研究金属离子钝化剂对胶清橡胶硫化性能,物理机械性能及热氧老化性能的影响。结果表明,加入金属离子钝化剂,对胶清橡胶的硫化性能和物理机械性能的影响较小,但是能够明显提高胶清橡胶的热氧老化性能。NaCA和EDTA-2Na在凝固前加入胶清对提高胶清橡胶的热氧老化性能和热稳定性效果更好,而STPP则是在混炼过程中添加效果更好。     

无氨保存胶清及胶清胶性能的研究

采用水溶性、不挥发性的广谱抗菌剂——三嗪衍生物(HY)作为鲜胶乳的新型无氨保存剂,研究了HY对胶清凝固总用酸量、胶清胶及胶清胶硫化胶片性能的影响。结果表明,HY保存胶清凝固总用酸量大大减少,除氮含量略微超标外,胶清胶的各项指标均达到1级胶清胶的标准,胶清胶的塑性保持率(PRI)明显提高。HY胶清胶硫化胶片的拉伸强度和耐热氧老化能力均优于氨胶清胶硫化胶片。热解重量分析(TGA)结果表明,HY和氨胶清胶硫化胶片热氧降解均为2步反应,耐热氧降解能力基本相同。     

Refining natural rubber matrix for electrically stimulated transdermal drug delivery

This work focuses on the enhancement of transdermal delivery of indomethacin (IN) from natural rubber matrix by deproteinization, the addition of ethylene glycol (EG) as a plasticizer, and the enlarged matrix size under electrical field. The starting double-centrifuge natural rubber (DCNR) was deproteinized to produce the deproteinized natural rubber (DPNR). Both DCNR and DPNR patches were fabricated by the UV curing method, and blended with EG to enhance the IN loading and release–permeation. Using a pig skin to simulate the human skin, the IN release–permeation was found to increase with increasing plasticizer, removed protein, and applied electrical potential.     

天然胶乳的挥发脂肪酸值与电导率关系的探索

通过改变挥发脂肪酸含量、无机盐浓度、外界温度，探索天然胶乳的挥发脂肪酸值与电导率的关系。     

Chitin nanocrystals reticulated self-assembled architecture reinforces deproteinized natural rubber latex film

Natural rubber (NR) latex was initially deproteinized, then, the interactions between chitin nanocrystals (ChNCs) and deproteinized natural rubber (DNR) latex particles in an aqueous system and the properties of DNR/ChNCs composites were investigated. Composite films were obtained by casting and evaporating off the prevulcanized DNR/ChNCs complexation rather than simply mixing of DNR latex and ChNCs suspension. The results of DLS and TEM confirmed that this kind of complexation was formed between negative charged DNR and positively charged ChNCs by self-assembly. The tensile strength of composite films containing 4 wt% ChNCs was 25.00 ± 1.42 MPa, which was 3.11 multiples of the pure pre-vulcanized DNR. DNR/ChNCs composite films could provide excellent mechanical properties and avoid allergies caused by proteins in NR latex.     

Removal of proteins from natural rubber with urea and its application to continuous processes

The removal of proteins from natural rubber through a batch process was studied by the incubation of the rubber latex with urea in the presence of sodium dodecyl sulfate. Under suitable conditions, the total nitrogen content of deproteinized natural rubber (DPNR) decreased from 0.38 to 0.02 wt % after incubation for 10 min; this was similar to that of the rubber deproteinized with a proteolytic enzyme for 12 h. For applications, continuous incubation and centrifugation were individually investigated by the use of a semicircular channel and a continuous centrifuge, respectively, to scale up DPNR preparation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

丁腈橡胶/聚氯乙烯/有机蒙脱土纳米复合材料的结构与性能

采用胶乳共沉法和直接共混法制备了丁腈橡胶／聚氯乙稀／有机蒙脱土（NBR／PVC／OMMT）纳米复合材料。通过X射线衍射（XRD）法和透射电子显微镜（TEM）法对NBR／PVC／OMMT纳米复合材料的结构进行了袁征,并研究了复合材料的力学性能、耐油性能和耐老化性能。结果表明,2种方法所获得的复合材料是插层型纳米复合材料;胶乳共沉法制备的纳米复合材料中OMMT的分散更为均匀,其力学性能、耐油性能和耐老化性能优于直接共混法制备的复合材料。     

Polymer electrolyte membrane with nanomatrix channel prepared by sulfonation of natural rubber grafted with polystyrene

High‐proton‐conductive polymer electrolyte with a nanomatrix channel was prepared by graft copolymerization of styrene onto deproteinized natural rubber followed by sulfonation with chlorosulfonic acid. First, natural rubber latex was purified with urea in the presence of surfactant to remove almost all proteins present in the rubber. Second, graft copolymerization of styrene onto deproteinized natural rubber was carried out with tert‐butyl hydroperoxide/tetraethylenepentamine as an initiator at 30°C in latex stage. The graft‐copolymerized natural rubber (DPNR‐graft‐PS) was sulfonated with chlorosulfonic acid in chloroform solution at an ambient temperature. The resulting sulfonated DPNR‐graft‐PS was characterized by FTIR spectroscopy, solid state ¹³C CP/MAS NMR spectroscopy, elemental analysis, and transmission electron microscopy. High proton conductivity of about 0.1 S/cm, less water uptake of 24 wt % and comparatively good stress at break of 9 MPa were accomplished at suitable contents of styrene units and sulfur, i.e., 32 wt % and 75 mol %, respectively. The high proton conductivity, excellent stability, and good mechanical properties were associated with not only the formation of the nanomatrix channel but also a specific concentration of sulfuric acid group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Effect of In Situ Polymerization of Styrene onto Natural Rubber on Adhesion Properties of Styrene-Natural Rubber (SNR) Adhesives

Styrene-based deproteinized natural rubber (SNR) latex was synthesized by in situ polymerization. Three pre-vulcanization systems [conventional-cured (CV), semi-efficient-cured (Semi-EV), and efficient-cured (EV)] were studied in terms of tensile and adhesion properties. Good tensile properties were observed for CV and EV SNR. The Semi-EV SNR showed the best adhesion properties based on the good anchorage performance in all substrate pairings (polystyrene–polystyrene, polystyrene–rubber, and rubber–rubber). The pH modification on SNR latex via KOH addition has beneficial effects of removing protein layers, resulting in more styrene grafting sites in the rubber molecules. Consequently, the tensile and adhesion properties of the SNR are improved as more styrene polymers are grafted onto the rubber matrix. Semi-EV SNR with pH 12 has superior adhesive performance; hence, it is suitable for use as a pressure-sensitive adhesive.     

Comparative study of the elasticity and permeability of vulcanized films made with skim and cream natural rubber latex

The purpose of this study was to gain a clearer picture of the structure and properties of vulcanized films made with skim and cream latex from Hevea brasiliensis. The two properties targeted for this study were the elasticity of the films and their permeability to acetone. Surface characterization by atomic force microscopy revealed that vulcanization substantially modified the structure of the films compared to unvulcanized films. Unlike unvulcanized films, particle identity was retained in the vulcanized films made with cream latex, even after 4 weeks of aging. In addition, skim latex gave vulcanized films with greater elasticity than those obtained with cream latex. On the basis of the structural characterization carried out on the latex and films and information from the literature, the greater elasticity of the skim films arose from more entanglements between polyisoprene chains and associations between proteins. Despite differences in the structure, the acetone permeability was very similar for skim and cream vulcanized films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hyperdeproteinized natural rubber prepared with urea

Preparation of hyperdeproteinized natural rubber was made from fresh latex and preserved high‐ammonia latex by treatment with urea in the presence of sodium dodecyl sulfate. Concentration of urea, temperature, and time for the incubation were investigated to remove the proteins effectively. Under the best conditions, the total nitrogen content and amount of allergenic proteins for the deproteinized rubbers were 0.005 wt % and 1.0 μg/ml, respectively, which were less than those of natural rubber deproteinized with proteolytic enzyme. The hyper‐deproteinized natural rubber was proved through FT IR spectroscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 555–559, 2004     

Characteristics of Oil and Skim in Enzyme-Assisted Aqueous Extraction of Soybeans

The economic viability of enzyme-assisted aqueous extraction processing (EAEP) of soybeans depends on properties and potential applications of all fractions (skim and insolubles as well as oil). EAEP oil contained lower free fatty acid, phosphorus, and tocopherol contents, similar unsaponifiable matter levels, and higher degrees of oxidation (peroxide and p-anisidine values) than hexane-extracted oil. The phospholipid profile of EAEP fractions was mainly composed of phosphatidic acid, followed by phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine. Most of phospholipids were present in the skim, except for phosphatidic acid, which was the major phospholipid in the cream fraction. Skim and cream contained 55 and 3 % of the soluble carbohydrates in the original extruded flakes, respectively. Soluble carbohydrates of the skim were mainly composed of stachyose (5.8 ± 0.8 mg/mL) and sucrose (9.9 ± 0.8 mg/mL), which were hydrolyzed into glucose, galactose, and fructose after addition of α-galactosidase. Skim and cream peptides contained <20 kDa MW molecules. About 71 % of the skim peptides were <20 kDa MW, with 49 % being <1.35 kDa MW, 22 % being 17–1.35 kDa MW, and 29 % being 44–670 kDa MW. Skim protein and carbohydrate contents make this fraction suitable for replacing water in ethanol fermentations, thereby improving the fermentation rate/production and the nutritional quality of distiller’s dried grains with solubles.     

Preparation and graft‐copolymerization of hydrogenated natural rubber in latex stage

Preparation and graft‐copolymerization of hydrogenated natural rubber are performed in latex stage after removal of proteins from the rubber with urea and surfactant. Hydrogenation of deproteinized natural rubber (DPNR) latex is carried out with palladium catalyst under hydrogen atmosphere. The hydrogenated DPNR (HDPNR) is crosslinked with a peroxide followed by graft‐copolymerization of styrene (Sty) and acrylonitrile (AN) in latex stage in order to prepare a graft‐copolymer of crosslinked HDPNR with poly(Sty‐co‐AN) (HDPNR‐graft‐PSAN). Characterization of the products is performed by nuclear magnetic resonance spectroscopy. The conversion of hydrogenation is investigated with respect to the catalyst feed, acidity (pH), and dry rubber content. In the resulting HDPNR‐graft‐PSAN, mole fraction of AN and Sty is 1.4 and 5.8 mol %, respectively. The graft‐copolymer is used to improve properties of PSAN as an impact modifier. The Charpy impact strength of crosslinked HDPNR‐graft‐PSAN/PSAN is about eight times as high as that of PSAN. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42435.     

Mechanical properties of thermoplastic elastomeric blends of chitosan and natural rubber latex

Thermoplastic chitosan/natural rubber blends (Cs/NR) were prepared from natural rubber latex and chitosan by solution casting technique. The blends were characterized by mechanical analysis (stress–strain) and the mechanical properties were found to vary with chitosan/natural rubber ratios. Experimental values were compared with different theoretical models. Effect of thermal aging on mechanical properties was also investigated. Dicumyl peroxide was used as the crosslinking agent. The effect of crosslinking on mechanical properties of Cs/NR has also been studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

不同割龄橡胶树RRIM600胶乳组份及性能的研究

本论文研究了割龄3年、割龄13年、割龄20年、割龄24年和割龄28年5种不同割龄的RRIM600天然胶乳的性能。主要研究了天然胶乳粒径,生胶性能,混炼胶的硫化特性以及硫化胶的力学性能。结果表明,割龄28年胶树所得天然胶乳平均粒径最小,胶粒的分布范围较窄,分散性较好;割龄20年橡胶树生胶的P₀和门尼黏度较大,割龄为20年和28年橡胶树所得天然橡胶拉伸强度和撕裂强度较大。     

The influence of surface structure of low industrial grade seaweed and semi‐refined carrageenan on mechanical and physical properties of natural rubber latex composites

Composites consisting of natural rubber (NR) latex as their matrix and low industrial grade seaweed (LIGS) and its extractive (semirefined carrageenan, SRC‐LIGS) as the filler were prepared via normal prevulcanization process. An analysis regarding the particle size and morphology of seaweed (LIGS and SRC‐LIGS), as well as surface properties and mechanical properties (tensile and tear properties) of NR latex composites, was consequently generated. Furthermore, post‐processing treatment for NR latex composites have also been studied, specifically involving leaching, heat aging, water absorption, and soil burial. The particle size of LIGS and SRC‐LIGS obtained was recorded to be lower than 100 μm. Thus, the results are indicative of SRC‐LIGS's role in improving the thermal properties of NR latex composites. After 8 weeks of soil burial, the incorporation of LIGS and SRC‐LIGS into the NR latex composites has accelerated biodegradation processes, thus highlighting their advantage as biodegradable fillers. These properties have consequently contributed to SRC‐LIGS/NR latex composites as a potential composite for use in biodegradable applications, such as polybag for pottery and plants. J. VINYL ADDIT. TECHNOL., 25:278–286, 2019. © 2018 Society of Plastics Engineers