Latex Samples Research Articles

Headspace, Solid-phase Micro-extraction, Gas Chromatographic-Mass Spectrometric Analysis of Terpenoids in the Latex of Euphorbia Species

The volatile and semi-volatile terpenoids in the latex of Euphorbia amygdaloides, E. exigua, E. helioscopia, and E. peplus were analyzed by headspace, solid-phase micro-extraction (HS-SPME), coupled with gas chromatography-mass spectrometry. The volatiles were extracted using a 100 microm polydimethylsiloxane SPME fiber under optimized extraction conditions. The compounds detected encompassed a range of chemical classes, but only terpenoids were evaluated. Only sesquiterpene hydrocarbons were detected in the tested samples of E. exigua, E. helioscopia, and E. peplus, with beta-caryophyllene being the major one, but were never recorded in latex samples of E. amygdaloides, in which only the diterpene hydrocarbon kaur-16-ene was detected. Alpha-Humulene was consistently found in samples of E. helioscopia, and E. peplus, but never in those of the other two species. These preliminary results show that the developed procedure is suitable for the analysis of small samples of Euphorbia latex and that, for each individual species, there is very little qualitative difference between samples, regardless of either place or date of collection.

Environmental fate of processed natural rubber latex

In this study, processed natural rubber latex was degraded in outdoor aquatic microcosms, under a number of treatment scenarios for 200 days. The analytical strategy adopted aimed to characterise a range of volatile, semi-volatile and non-volatile substances. Zinc, was shown to migrate from the latex into solution and increase in concentration over time. Dissolved compounds for which predicted formulas were generated largely consisted of oxygen containing compounds, and are potential oxidised polyisoprene oligomers of various chain lengths. A classification of samples based on principal component analysis showed a clear separation of the degraded latex samples from the representative controls. This technique identified an increase in the complexity of the substances produced and showed that these substances undergo further degradation and transformation processes. A number of volatile substances were also identified indicating the atmosphere to be a potential receiving environmental compartment for polymer degradates. Overall, the results show that complex mixtures of substances are produced when polymer-based materials degrade under environmental conditions.

Effect of low frequency harvesting in <i>Hevea brasiliensis</i> on major raw rubber properties

Harvesting latex, a key activity in the production of natural rubber (NR), involves repeated tapping of the bark on the main trunk of the trees. Low frequency harvesting (LFH) systems are only economically feasible with the use of Ethephon (ET) which stimulates the tree to provide high yield per tap as a compensation for the yield loss due to lowering the tapping frequency. Ethephon concentration and its frequency of application may vary with the frequency of harvesting used. Latex samples were collected from genotypes; RRIC 100, RRIC 102, RRIC 121 and RRIC 130 harvested under S/2 d2, S/2 d3, S/2 d4 and S/2 d6 (i.e. tapping half of the spiral of tree once in two, three, four and six days, respectively) systems were processed into lace crepe and assessed for raw rubber properties viz. initial plasticity (Po), plasticity retention index (PRI), Mooney viscosity (VR), colour, nitrogen and ash content. No significant differences were observed among different LFH systems with respect to each raw rubber property tested. However, clonal differences in those raw rubber properties were prominent. Therefore, the study revealed that the low frequency harvesting systems tested with Ethephon stimulation do not have any effect on the quality of raw rubber produced.

Drying of Porous Coating: Influence of Coating Composition

The influence of the coating composition of a porous paper coating on the evaporation rate of water contained in the sample has been studied experimentally. For low-content latex samples, drying was found to be mainly controlled by capillarity, perhaps also in the form of thin film pore surface feature/wall wetting, which drew water from the connected pores to the drying surface or near the surface. This led to a lengthy constant drying rate period (CDRP) where nearly 70% of the saturated water was evaporated. High-content latex samples, characterized by low porosity and permeability showed shorter CDRP and lengthy falling drying rate period. The drying rate curve varied linearly with time in the CDRP and with the square root of time in the falling rate period, indicating a diffusive controlled mechanism. Low latex content samples took less time to dry, which can be inferred to mean they require less drying energy.

Single-Frequency-Based Dry Rubber Content Determination Technique for In-Field Measurement Application

In this paper, it is shown that extensive characterization and modeling of dielectric permittivity of rubber latex enables dry rubber content (DRC) to be accurately determined using a measurement at a single microwave frequency. The model is demonstrated in a low-cost sensing system based on a six-port reflectometer that is suitable for application in the field. To develop an accurate model, a wide range of samples (with the DRC in the range 28%–61%) is first measured using the Agilent Technologies 85070E dielectric probe system for a range of frequencies and at temperatures from 15 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> to 39 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> . This data is then used to determine the parameters of a dielectric mixture model, which is based on the assumption that rubber latex is a diphase liquid consisting of the water and solid rubber. To take the effect of temperature and signal frequency on the molecular polarization behavior into account, the dielectric permittivity of the water is described using a Debye-type relaxation spectral function; and the frequency-dependant polarization parameter of neighboring inclusions is applied to the dielectric mixture model. After determining all the model parameters, it is then shown that the measurement of the sample's temperature and dielectric permittivity at a single frequency is sufficient to determine the DRC with a high degree of accuracy. Compared with the measurements made with the standard oven-drying method, using a single 2.5 GHz measurement the technique exhibits 0.36% DRC of mean absolute error with 0.28% DRC standard deviation, over the temperature range 15 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex> </formula> –39 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> . Finally, the technique is implemented with a six-port reflectometer. The measurement system employing the model is applied and tested with several fresh rubber latex samples. A wide range of measured results confirm the validity of the technique.

First report of papaya meleira virus (PMeV) in Mexico

Papaya meleira virus (PMeV), causal agent of meleira or sticky disease, is a double-stranded RNA (dsRNA) virus which has been previously reported only in Brazil. A study was carried out in order to verify the presence and occurrence of PMeV in Mexico. Latex samples from symptomatic and asymptomatic papaya fruits were collected in Quintana Roo state papaya orchards, where the first symptoms of PMeV were observed, and from 29 different municipalities located in ten papaya producer states in Mexico. A molecular protocol based on nucleic acid extraction was used for the diagnosis and a virus 12 Kb dsRNA distinctive band was observed in all PMeV infected plants. Around 46% of the evaluated plants were positive for this pathogen. Presence of the virus had been confirmed in seven states indicating the potential damage that PMeV could cause in the papaya crop in Mexico. The molecular analysis used allowed the diagnosis of infected plants without symptoms and facilitated the diagnosis in flowers and small papaya fruits also. The early diagnosis of PMeV will allow papaya producers to take appropriate and timely control measures. This is the first report of Papaya meleira virus in Mexico.

Design and analysis of the homogeneous and heterogeneous distribution of water confined within colloidal polymer particles

Water is known to distribute within polymeric films in multiple states differentiable by the energy of association. Potentiometric swelling of carboxylated latex samples and subsequent differential scanning calorimetry (DSC) and thermogravimetric analysis verified this distribution of water, specifically confined within colloidal nanoparticle dimensions. DSC cooling curves can delineate between the freezable bound and freezable unbound water at low total water content but become difficult to distinguish the freezable bound contribution at high total water content. Of note is that the ratio of weakly bound water in the secondary layer to the water strongly hydrogen-bound to the polymer is approximately constant regardless of carboxylic acid type and, in fact, is greater for the case of the hydrophobic base polymer. Aside from its distribution within the particles, the total water content also appeared to be more related to the hydroplasticized glass point of the polymer colloid as opposed to the polarity of the polymer.

Characterization of a miniemulsion by DLS and SANS

Dynamic light scattering (DLS), small angle neutron scattering (SANS) and transmission electronic microscopy (TEM) were used for the size determination of the poly(trifluoropropylmethyl)siloxane (PTFPMS) nanoparticles obtained by miniemulsion polymerization. The presence of large particles with a narrow size distribution as deduced from the DLS experiments on the latex sample was taken into account in the SANS data analysis by the introduction of a bimodal size distribution including a small particle population. It was shown that the contribution to scattering of the large particle component consistent with the SANS data should be less than about 45% of the total particle volume fraction. These results were corroborated by the spherical particle shape and the quite large particle size distribution observed on the TEM images. The DLS experimental procedures exploiting merely the cumulant analysis of the autocorrelation function for size determination in routine usage in the field of miniemulsions should thus be practiced with caution.

Effect of acrylic monomer content on the properties of waterborne poly(urethane‐urea)/acrylic hybrid materials

AbstractStable waterborne poly(urethane‐urea) (WBPU; soft segment content: 57%; dimethylol propionic acid: 19 mol %/5.8 wt %)–polyacrylate(methyl methacrylate/n‐butyl acrylate) (weight ratio: 4/1) hybrid latex (emulsions) with different acrylic contents [0, 10, 20, 30, and 40 wt % based on poly(urethane‐urea)] and without external surfactant were successfully prepared by in situ polymerization during a prepolymer mixing process. However, the as‐polymerized hybrid latex containing 50 wt % of acrylic monomer content was found to be unstable, indicating that about 50 wt % of acrylic monomer content was beyond the limit value of self‐emulsifying ability of WBPU anionomer prepared in this study. The breadth of particle size distribution of hybrid latex increased markedly from 20–75 to 55–275 nm with increasing acrylic monomer content from 0 to 40 wt %. The pristine WBPU and hybrid latex samples containing 10, 20, and 30 wt % of acrylic monomer showed unimodal distributions, whereas the hybrid sample having 40 wt % acrylic monomer content displayed a bimodal distribution with the broadest breadth. As acrylic monomer content increased, the yield point of stress–strain curve, hardness, glass transition, and water resistance of hybrid film samples increased, whereas their abrasion resistance, elongation at break, and elasticity decreased. The tensile strength of hybrid film samples (10–30 wt % of acrylic monomer content) was almost the same as that of pristine WBPU film sample, indicating the intimate molecular mixing between poly(urethane‐urea) and polyacrylate molecules in hybrids. However, the hybrid sample having 40 wt % acrylic monomer showed significantly diminished performance, which might be due to the deviation from intimate molecular mixing. From these results, the optimum acrylic monomer content was found to be about 30 wt %, which realized reasonably advantages of both poly(urethane‐urea) and acrylic polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

REMOVING EXTRACTABLE PROTEINS IN NATURAL RUBBER LATEX BY CALCIUM CHLORIDE FROM CHICKEN EGGSHELLS

Abstract Controlling the level of the extractable protein contents in a natural rubber latex is important to the sensitization of natural rubber latex products users. Allergies caused by latex products cause a serious problem in which the sweat removes proteins and allowing a skin contact causing allergic reactions. Calcium oxide from calcined chicken eggshells at 900 °C for 1 h was dissolved in 2M HCl (CaCl2) and used as the thickening agent in which it can modify the protein structure. The eggshells were characterized by the particle size analysis, the impedance analysis, simultaneous thermal analysis (STA), x-ray diffraction (XRD), and Fourier transform infrared spectra (FTIR). Calcium chloride (CaCl2) interacts with the protein molecules and the solvent ions through the hydrogen bonding and the electrostatic interactions driving the extractable protein toward the film surface. Sodium dodecyl sulphate was used as the stabilizer in the natural rubber latex film formation. The extractable protein contents were measured and determined by the modified Lowry method. The concentrated latex samples were further characterized by FTIR, scanning electron microscope, and XRD and the results were reported here. Moreover, near infrared was used to measure the extractable protein spectra of the concentrated latex compounds in the region of 1100–2500 nm.

Latex aging: The effects of coalescing agents and thermal annealing on the morphology of composite latex particles

AbstractMany composite polymer latices are produced with nonequilibrium particle morphologies and these can be prone to structural changes with the time of storage. Here we report on the use of coalescing agents, and separately thermal annealing to follow the morphology changes with aging time. Two coalescing agents with very different water solubilities were used to plasticize the latex polymers. During months of storage time the polymer particles were analyzed via differential scanning calorimetry and transmission electron microscopy. A parallel set of aging experiments were carried out for the same latices where the change agent was simple thermal annealing. Both latex and dry polymer samples were annealed at temperatures above 100 °C and for various periods of time. Both sets of experiments lead to the conclusion that when the aging temperature is at or above the effective glass transition temperature (taking into account solvent plasticization) of the glassiest of the polymers in a two‐component latex, morphological change can be rather fast and easily characterized. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1583–1589, 2011

Proteolytic activity in latices of Asteraceae and Campanulaceae

In the order Asterales only two species are known to have proteolytic activity in their latices, first Taraxalisin from dandelion Taraxacum officinale Webb s.l., and second Parthenain from Guayule Parthenium argentatum L.. Both are characterized as serine endopeptidases [1]. Proteolytic enzymes isolated from plant latex have received special attention in the pharmaceutical industry and biotechnology due to their property of being active over wide range of temperature and pH. Nearly half of the commercially available enzymes are proteases, frequently used in food processing, tenderization of meat, brewing, cheese elaboration, bread manufacturing, leather and textile industries [1]. In this investigation the latex of 40 species of the Asteraceae family and 8 species of the Campanulaceae, which are not biochemical characterized before, were collected in the Botanical Garden Berlin. To determine proteolytic activity we used the fluorogenic substrate BODIPY FL- casein (Moleculare Probes, Inc., USA) [2]. To investigate the type of endopeptidases, the latex samples were pre-incubated with specific inhibitors for serine proteases (AEBSF (4-(2-Aminoethyl)-benzenesulfonyl fluoride hydrochloride), cysteine proteases (E64 (4-(2-Aminoethyl) benzenesulfonylfluoride hydrochloride)), aspartatic proteases (Pepstatin A) and metalloprotease (EDTA) and the remaining activity was determined. In both families highly active serine proteases were found.

Effect of rootstock on the scion of Hevea brasiliensis through metabolic analysis of latex samples by ¹H NMR

In this study, the effect of rootstock on grafting through metabolomic analysis of latex (Hevea brasiliensis) samples was verified by ¹H nuclear magnetic resonance (NMR) and multivariate data analysis. Sixteen metabolites present in the latex cytosol were characterized by NMR. PCA analysis showed that the latex samples of the RR and GR groups can be differentiated. The GR group samples present a metabolic profile similar to the RR group samples, while the RG group is in an intermediate position between RR and GG groups. Sucrose and formate contributed greatly to the separation obtained by PCA, presenting a good correlation between the results. ¹H NMR was an efficient technique to differentiate latex samples from different types of rootstocks and grafting and in the future could be used to predict rubber production by latex analysis.

New Technology and Applications on Microwave Sensor for Moisture Content Measurement

This paper presents the new technology and applications on microwave sensor for moisture content measurement. A dual-frequency microwave sensor based on circular microstrip antenna has been developed to measure moisture content(MC) of lossy liquids. The experiment is based on measurements of far-field reflection at two frequencies in the X-band,8.48 and 10.69GHz. Moisture content of the rubber latex samples can be determined with a standard error 0.49%.A prototype microwave based moisture sensor system suitable for the kiln drying of hardwood lumber has been developed. Using the prototype electronics and sensors, have obtained measurements of MC over the above MC range for red oak and yellow poplar with standard deviations of less than 1.5% MC at 4.5 to 6GHz.A smart active microwave sensor for measuring the moisture content of felts used in the paper milling industry and more generally of sheet-like materials is presented. An inversion procedure based on an Artificial Neural Network (ANN) approach is proposed in order to determine the moisture content of the felts. Finally the technical challenges and developing prospect of microwave sensors for Moisture Content Measurement are discussed.

Bacterial community associated with the trunk latex of Hancornia speciosa Gomes (Apocynaceae) grown in the northeast of Brazil

Prevention or cure of different illnesses through the use of plant latex is a worldwide known concept. The antifungal activity of Hancornia speciosa latex has been observed against Candida albicans. However, H. speciosa latex is not a sterile plant exudate and secondary metabolites produced by bacteria could be involved in fungal inhibition. In the present study, the bacterial communities of the latex from three H. speciosa trees were characterized using traditional plating and molecular methods. Twelve strains isolated from the latex samples were clustered into four groups by amplified ribosomal DNA restriction analysis (ARDRA). One representative of each group was sequenced and they were identified as belonging to the genera Bacillus, Klebsiella, Enterobacter and Escherichia. None of the 12 isolates showed antifungal activity against C. albicans. A lack of a microbial origin for the antifungal properties of latex was noted. DGGE profiles generated from each of the three latex samples showed unique patterns. Sequencing of the DGGE bands demonstrated the affiliation with the genera Klebsiella, Pantoea, Enterobacter and Burkholderia. In addition, clone libraries were generated and the phylogenetic distribution of the 50 analyzed clones was similar to that obtained using DGGE. The presence of some potential pathogens should be considered before using H. speciosa latex in folk medicine.

Accurate particle size distribution determination by nanoparticle tracking analysis based on 2-D Brownian dynamics simulation

A physical model is presented to simulate the average step length distribution during nanoparticle tracking analysis experiments as a function of the particle size distribution and the distribution of the number of steps within the tracks. Considering only tracks of at least five steps, numerical simulation could be replaced by a normal distribution approximation. Based on this model, simulation of a step length distribution allows obtaining a much more reliable estimation of the particle size distribution, thereby reducing the artificial broadening of the distribution, as is typically observed by direct conversion of step length to particle size data. As this fitting procedure also allowed including data from particles that were followed for a relatively low number of steps, the measurement time could be reduced for particles that are known to be monodisperse. Whereas the inversion is less sensitive towards the particle size distribution width, still similar values were obtained for both the average diameter and standard deviation of a polystyrene latex sample irrespective of the track length, provided that the latter included at least five steps.

Inhibitory profile of latex-proteases in the genus Euphorbia

The latex of some plant families such as Apocynaceae, Asclepiadaceae, Asteraceae, Caricaceae, Convolvulaceae, Euphorbiaceae, and Moraceae are known to contain endopeptidases. Proteolytic enzymes from plant latex have received special attention in the pharmaceutical industry and biotechnology due to their property of being active over wide range of temperature and pH. Nearly half of the commercially available enzymes are proteases, frequently used in food processing, tenderization of meat, brewing, cheese elaboration, bread manufacturing, leather and textile industries [1]. In the genus Euphorbia (Euphorbiaceae) 64 different species are mentioned to have proteolytic activity in their latices [2]. In this investigation the latex of 23 species of the genus Euphorbia, which are not characterised before, were collected in the Botanical Garden Berlin. To determine proteolytic activity we used the fluorogenic substrate BODIPY FL- casein (Moleculare Probes, Inc., USA) [3]. All tested samples show proteolytic activity. To investigate the type of endopeptidases, the latex samples were pre-incubated with specific inhibitors for serine (AEBSF (4-(2-Aminoethyl)-benzenesulfonyl fluoride hydrochloride)-, cysteine(E64 (4-(2-Aminoethyl)benzenesulfonylfluoride hydrochloride)) -, aspartatic (Pepstatin A)- and metalloprotease (EDTA) and the remaining activity was determined. 18 plants were strongly inhibited only by serine specific inhibitor, one plant was not influenced by any inhibitor and 4 plants were influenced by at least two inhibitors and had still a remaining proteolytic activity.

Relationships between physiological parameters of latex and technological properties of processed natural rubber

Natural rubber must be technically specified for various uses. Variability in technological properties of raw nat-ural rubber leads to problems of grading. A study was conducted to establish relationships between physio-logical parameters of latex and technological properties of the raw rubber. The latex samples were analysed by micro-latex diagnosis technique and the relevant technological properties of the processed rubber estimated usi-ng International Standard organization (ISO) procedures. Correlations were found between physiological para-meters and technological properties of processed crumbs; specifically, between the plasticity retention index, Mooney viscosity, Initial Wallace plasticity and inorganic phosphorus, total solid content and sucrose content. The relationships varied with the clones. The best empirical equations fit describing the relationship between physiological parameters of latex and technological properties of the raw rubber were polynomials, while the master equation was a power function with coefficient of determination of 0.84. The values of technological properties of raw rubber could be predicted from the values of some physiological parameters of the latex, and such empirical relationships would assist farmers to forecast values of the technological properties, and modify the properties as required prior to processing.

Estimation of dry rubber content in natural rubber latex by differential scanning calorimetry

Differential Scanning Calorimetry (DSC) is employed to study the changes in enthalpy of natural rubber latex samples when heated under a controlled temperature program. It is found that the mass normalized areas of the DSC curves between room temperature and 170 °C for different latex samples are inversely proportional to the dry rubber content (DRC) of the samples, measured following the weighing and drying method. The changes in total enthalpy of the samples in this temperature range are interpreted as due to the variations in the quantity of water present in the samples. The measurements have been repeated by diluting selected samples with known quantities of water, and it is found that the normalized areas of the DSC curves are directly proportional to the amount of water added to the latex. The method can be used to estimate the DRC of natural rubber latex accurately. Its advantages and limitations are discussed.

Effect of Hydroplasticization on Polymer Diffusion in Poly(butyl acrylate-co-methyl methacrylate) and Poly(2-ethylhexyl acrylate-co-tert-butyl methacrylate) Latex Films

We compare the influence of humidity on the polymer diffusion rate in films formed from two different polymer latex samples whose polymers have the same glass transition temperature (Tg ≈ 12 °C) but different hydrophilicity: poly(butyl acrylate-co-methyl methacrylate), P(BA−MMA), and the more hydrophobic poly(2-ethylhexyl acrylate-co-tert-butyl methacrylate), P(EHA−tBMA). The diffusion process was monitored by fluorescence resonance energy transfer (FRET) at 25 °C and at 0, 23, 54, 85 and 98% relative humidities. The results show that the polymers diffused more rapidly in films aged at higher humidities, and thus were characterized by higher apparent diffusion coefficients (Dapp). By performing a master curve analysis, we obtained humidity related shift factors (aH). Not all the water taken up by these latex films contributes to enhance diffusion rates. Some of the water absorbed at high humidities is present in the form of water pools and microcavities (free water) and does not actively contribute to plasticization. We used FTIR spectra to obtain information about how water resides in the copolymer films. Although water is poorly miscible with most polymers, our results show that water molecules dispersed molecularly among the chains are highly efficient as a plasticizer and a promoter of polymer diffusion in latex films.