Latex-based nanocomposites

Nanoparticles have been widely used as filler in polymer because of their unique reinforcing effect. There are many compounding methods for nanocomposites. The recent development on latex nanocomposites, a group of special nanocomposites, is reviewed in this chapter. They include carbon black/latex nanocomposite, silica/latex nanocomposite, layered silicate/latex nanocomposite, ZnO/latex nanocomposite, carbon nanotubellatex nanocomposite, lignin/latex nanocomposite, starch/latex nanocomposite, nano-fiber/latex nanocomposite, and Chitin whiskers/latex nanocomposite. Advanced compounding techniques and the latest advance on these latex nanocomposites are described. The nanoreinforcing theories of latex nanocomposites are also studied.

Hypoallergenic variants of the major latex allergen Hev b 6.01 retaining human T lymphocyte reactivity

Hev b 6.01 is a major allergen of natural rubber latex with sensitization of 70–86% of latex glove-allergic subjects. Recently, we mapped the immunodominant T cell sites of Hev b 6.01 to the highly IgE-reactive hevein (Hev b 6.02) domain. Hev b 6.01 contains 14 cysteine residues with multiple disulphide bridges stabilizing tertiary conformation. With the goal of a standardized specific immunotherapy we developed hypoallergenic Hev b 6.01 mutants by site-directed mutagenesis of selected cysteine residues (3, 12, 17, and 41) within the Hev b 6.02 domain. Peptides corresponding to the Hev b 6.02 domain of two of the mutants were also synthesized. These mutants and peptide variants showed markedly decreased or ablated latex-allergic patient serum IgE binding by immunoblotting and ELISA. Basophil activation testing confirmed markedly decreased activation with successive cysteine substitutions of the mutants and complete abrogation with the Hev b 6.02 (Cys 3, 12, 17, 41 Ala) peptide. Retention of T cell reactivity is crucial for effective specific immunotherapy and all mutants and peptide variants maintained their latex-specific T cell reactivity. The ablated allergenicity but retained T cell reactivity of the Hev b 6.02 (Cys 3, 12, 17, 41 Ala) peptide suggests this peptide is a suitable candidate for inclusion in a latex immunotherapy preparation.

Self-assembled natural rubber/multi-walled carbon nanotube composites using latex compounding techniques

Functionalization of multi-walled carbon nanotubes (MWCNTs) plays an important role in eliminating nanotube aggregation for reinforcing polymeric materials. We prepared a new class of natural rubber (NR)/MWCNT composites by using latex compounding and self-assembly technique. The MWCNTs were functionalized with mixed acids (H2SO₄/HNO₃ = 3:1, volume ratio) and then assembled with poly (diallyldimethylammonium chloride) and latex particles. The Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy were used to investigate the assembling mechanism between latex particles and MWCNTs. It is found that MWCNTs are homogenously dispersed in the natural rubber (NR) latex as individual nanotubes since strong self-aggregation of MWCNTs has been greatly depressed with their surface functionalization. The well-dispersed MWCNTs produce a remarkable increase in the tensile strength of NR even when the amount of MWCNTs is only 1 wt.%. Dynamic mechanical analysis shows that the glass transition temperature of composites is higher and the inner-thermogenesis and thermal stability of NR/MWCNT composites are better, when compared to those of the pure NR. The marked improvement in these properties is largely due to the strong interfacial adhesion between the NR phase and MWCNTs. Functionalization of MWCNTs represents a potentially powerful technology for significant reinforcement of natural rubber materials.

Forces measured between latex spheres in aqueous electrolyte : Non-DLVO behavior and sensitivity to dissolved gas

An atomic force microscope was used to measure the forces acting between two polystyrene latex spheres in aqueous media. The results show an electrostatic repulsion at large separations which is overtaken by an attractive “hook” that pulls the two spheres into contact from a considerable range (20−400 nm), much larger than could be expected for a van der Waals attraction. The range of operation of this attraction varies from one experiment to another and is not correlated with electrolyte concentration. However, the range is found to decrease significantly when the level of dissolved gas in the water is reduced.

Rubber latex yield and physiology of rubber tree with tea tree oil treatments

To examine the effects of tea tree oil on rubber latex yield and the resulting latex physiological parameters of rubber tree （Hevea brasiliensis），clean water and 20%，40%，60%，80% and 100% of tea tree oil were applied on the tapping cut of rubber trees. The data were analyzed by Duncan test and its results showed that when compared to clean water （ck），80% and 100% of tea tree oil stimulation significantly promoted rubber latex yield（P＜0.05）. In addition，the latex physiological parameters changed with the sucrose content（P＜0.01），magnesium ion content （P＜0.01） and inorganic phosphorus content （P＜0.01） of latex significantly increasing and thiol content significantly deceasing （P＜0.01）. The effect of tea tree oil treatments on rubber yield was similar to the impact of 0.5% ethrel stimulation. However，compared to ethrel stimulation，100% tea tree oil treatment significantly increased dry rubber and sucrose contents （P＜0.01） and decreased thiol content （P＜0.01）. Thus，tea tree oil treatment involved different latex yield promotion mechanisms than that of ethrel stimulation.

Preparation and characterization of natural rubber/silica nanocomposites using rule of similarity in latex

Rule of similarity and latex compounding techniques were combined for the first time to prepare natural rubber/nanosilica (NR/SiO2) nanocomposite with core-shell nanosilica-poly (methyl methacrylate) (SiO 2-PMMA) particles and PMMA-modified natural rubber matrix (NR-PMMA). The microstructure of SiO2 and nanocomposites with different SiO 2 contents was characterized by fourier transform infrared spectroscopy (FTIR); the morphology of nanocomposites was investigated with scanning electron microscopy (SEM); the tensile strength was characterized by tensile testing machine and the thermal stability of composites was studied by thermal gravimetric analysis. Results showed that PMMA chains have successfully grafted onto the surface of SiO2, and the core-shell SiO 2-PMMA nanoparticles and NR-PMMA latex have been perfectly incorporated. SiO2-PMMA nanoparticles are evenly distributed over the NR matrix with an average size in the range of 60-100 nm at the low content (SiO2? 3 wt%), while aggregations are apparently observed when 5 wt% SiO2 is loaded. In addition, NR/SiO2 composities possess a considerable improvement in ageing resistance compared with the pure NR. The tensile strength of composite increases from 6.99 to 12.72 MPa, reaching the highest value at a 0.5 wt% SiO2 loading, and then the figure decreases gradually because of the aggregation of SiO2 nanoparticles. It is anticipated that the reported process is to provide a simple and economic way for preparing NR composites.

Effect of ultrasonic wave on latex production and quality of rubber tree

The effects of ultrasonic wave on tapping surface of ‘PR107’ rubber tree were studied. Daily production and cumulative production of latex were measured to estimate the effects of ultrasonic wave on latex production. The solid substance content, dry rubber content and mechanical stability of latex were determined to study the effects of ultrasonic wave on latex quality. Results showed that ultrasonic wave could increase both daily and cumulative production of latex and maintain latex basic quality. The daily production of latex was increased and appeared two peaks both in the ultrasound-treated rubber tree and the one with no treatment. The first peak appeared on the fifth day, and the latex production by ultrasound was 212.34 ml and the control was 141.75 ml The second peak appeared with the production 266.59 ml on the seventeenth day by ultrasound, while the control appeared on the thirteenth day with production of 193.5 ml. The latex cumulative production of ultrasound-treated trees was 209.56 ml higher than that of control in one month. There was little change in solid substance content and dry rubber content between different ultrasonic time. The best mechanical stability of latex was obtained by ultrasound-treating the rubber tree for 4-6 min. it was proved that the ultrasound was helpful in improving the latex production and quality. The application of ultrasonic wave on rubber tree is novel, and its mechanism is worth further research.

Primary prevention of latex related sensitisation and occupational asthma : a systematic review

Eight primary prevention intervention studies on natural rubber latex (NRL) published since 1990 were identified and reviewed. This is the largest evidence base of primary prevention studies for any occupational asthmagen. Review of this small and largely observational evidence base supports the following evidence statement: Substitution of powdered latex gloves with low protein powder‐free NRL gloves or latex‐free gloves greatly reduces NRL aeroallergens, NRL sensitisation, and NRL‐asthma in healthcare workers. Evidence in support of this statement is ranked SIGN level 2+, referring to well conducted case‐control or cohort studies with a low risk of confounding, bias, or chance and a moderate probability that the relationship is causal. Substitution of powdered latex gloves with low protein powder‐free NRL gloves or latex‐free gloves promises benefits to both workers' health and cost and human resource savings for employers. This message should be broadly disseminated beyond the hospital sector to include other healthcare settings (such as aged care facilities) as well as food service and other industries where latex gloves might be used.

Variation of phloem turgor pressure in Hevea brasiliensis: An implication for latex yield and tapping system optimization

Phloem turgor pressure (PTP) is the initial driving force for latex flow after a rubber tree is tapped and therefore plays an important role in rubber tree latex production. Variation in PTP with rubber tree clone, age, yield potential and commonly used Ethrel (an ethylene releaser) stimulation have, however, not been comprehensively studied to date. The aim of this study was to investigate these relations and examine whether PTP can be used as an index for rubber tree clone assessment and tapping system optimization. The results showed that: (1) the daily change of PTP in the foliation season suggests that a high PTP can ensure a high latex yield and tapping could be moved forward to midnight or earlier in the night; (2) the decrease of PTP from the basal to distal stem indicates the benefit of a controlled upward tapping system; (3) the logarithmic increase in PTP with rubber tree planting age and age-based mean girth suggests that the preferred age for the commencement of rubber tree tapping is eight years; (4) the change of PTP with regenerated bark age suggests that the regenerated bark could be exploited again after the second year; (5) PTP is positively related to the yield potential of rubber tree clones; (6) although Ethrel stimulation could not significantly increase the initial PTP of a rubber tree, it delays the recovery of PTP after tapping. Therefore, PTP is an indicator of rubber tree latex yield and can be used for tapping system optimization. © 2014 Elsevier B.V.

Latex dilution reaction during the tapping flow course of Hevea brasiliensis and the effect of Ethrel stimulation

The latex dilution reaction during the tapping flow course has been well documented and associated with the facilitation of tapping latex flow. However, its underlying mechanism has not experimentally examined. The latex total solid content, osmotic potential and phloem turgor pressure change during the tapping flow course were simultaneously measured to investigate the cause of water movement during the tapping flow course. It was found that there are three different stages for the laticifer water equilibrium during the tapping flow course. The tapping-induced rapid turgor pressure drop is the cause of the first stage water influx into laticifers, while osmoregulation prevails during water exchange in the second and third stages of tapping flow. Meanwhile, aquaporin expressions were, for the first time, investigated during the tapping flow course. The rapid transcript up-regulation of HbPIP1, HbPIP2;1 and HbPIP2;3 contributes to the latex dilution reaction. However, their activity gating cannot be ruled out. Ethrel stimulation can significantly dilute the corresponding latex fractions during the tapping flow course due to its up-regulations of HbPIP1, HbPIP2;1 and HbPIP2;3. Nevertheless, the latex dilution reaction pattern for the Ethrel treated trees did not change, except for a lower degree of dilution compared with the un-treated trees. All these results suggest that both phloem turgor pressure and aquaporins are involved in the latex dilution reaction during the tapping flow course.

Regulation of HbPIP2;3, a latex-abundant water transporter, is associated with latex dilution and yield in the rubber tree (Hevea brasiliensis Muell. Arg.)

Rubber tree (Hevea brasiliensis) latex, the source of natural rubber, is synthesised in the cytoplasm of laticifers. Efficient water inflow into laticifers is crucial for latex flow and production since it is the determinant of the total solid content of latex and its fluidity after tapping. As the mature laticifer vessel rings are devoid of plasmodesmata, water exchange between laticifers and surrounding cells is believed to be governed by plasma membrane intrinsic proteins (PIPs). To identify the most important PIP aquaporin in the water balance of laticifers, the transcriptional profiles of ten-latex-expressed PIPs were analysed. One of the most abundant transcripts, designated HbPIP2;3, was characterised in this study. When tested in Xenopus laevis oocytes HbPIP2;3 showed a high efficiency in increasing plasmalemma water conductance. Expression analysis indicated that the HbPIP2;3 gene was preferentially expressed in latex, and the transcripts were up-regulated by both wounding and exogenously applied Ethrel (a commonly-used ethylene releaser). Although regular tapping up-regulated the expression of HbPIP2;3 during the first few tappings of the virginal rubber trees, the transcriptional kinetics of HbPIP2;3 to Ethrel stimulation in the regularly tapped tree exhibited a similar pattern to that of the previously reported HbPIP2;1 in the virginal rubber trees. Furthermore, the mRNA level of HbPIP2;3 was associated with clonal yield potential and the Ethrel stimulation response. Together, these results have revealed the central regulatory role of HbPIP2;3 in laticifer water balance and ethylene stimulation of latex production in Hevea.