Effects of Frequency and Sonication Time on Ultrasonic Degradation of Natural Rubber Latex

2013 ◽  
Vol 747 ◽  
pp. 721-724 ◽  
Author(s):  
S. Utara ◽  
U. Moonart

Ultrasonic degradation of fresh latex was investigated at frequencies of 20 and 25 kHz, at a constant temperature of 25o C (±1o C) to avoid temperature-related effects. The time-dependent evolution of the molecular weight of the natural rubber latex was determined using gel permeation chromatography, and its structure by means of the fourier transform infrared (FTIR) technique. A 10 minute period of sonication resulted in reduction in the molecular weight of both the 20 and 25 kHz treated samples, the lowest average molecular weight () being obtained in the case of the 25 kHz sample. The of the 25 kHz sample also decreased with increasing latex concentration. However, after 30 minutes, fluctuations had occurred in both samples with respect to the and and also the molecular weight distributions, an effect possibly explained by the competing processes of chain scission and radically-induced cross-linking of the polymer chains. The FTIR results also suggest that the structure of polyisoprene is unaltered by ultrasonic wave treatment at these frequencies.

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
N. Ugur Kaya ◽  
Y. Avcibasi Guvenilir

Poly(ε-caprolactone) (PCL) macromonomers comprising acrylate end-functionality were synthesized via enzymatic ring-opening polymerization (eROP) by utilizing commercially availableCandida antarcticaLipase B (CALB), Novozyme-435. 2-Hydroxyethyl methacrylate (HEMA) was purposed to be the nucleophilic initiator in eROP. The side reactions generated due to the cleavage of ester bonds in HEMA and the growing polymer chains were investigated through altering polymerization period, initiator concentration, temperature, and enzyme concentration.1H NMR evaluations showed that minimum quantities of side reactions were in lower temperatures, initiator concentration, enzyme concentration, and lower monomer conversions. Gel permeation chromatography (GPC) results revealed that lower polydispersity along with number-average molecular weight of end-functionalized PCL macromonomers was obtained depending on higher initiator/monomer ratios, lower temperature (60°C), enzyme concentration (100 mg), and/or polymerization time (2 h). Furthermore, 0.1 HEMA/ε-caprolactone (CL) ratio had higher molecular weight than 0.5 HEMA/CL ratio, while keeping a close value of methacrylate transfer, total methacrylate end-groups, and lower polyester transfer.


1965 ◽  
Vol 38 (5) ◽  
pp. 1214-1227 ◽  
Author(s):  
E. M. Bevilacqua

Abstract Natural rubber is exposed to oxygen from the time that trees are tapped through its vulcanization and final use. Reaction with oxygen at each stage in its history affects its properties. Extensive studies have been made of the effects in later stages, on raw and vulcanized rubber; much less work has been done on the oxidation of latex. Fresh latex is a dilute aqueous emulsion in which the non-volatile content is approximately 90 per cent rubber hydrocarbon. The rest is a complex mixture of compounds, most of which are normal constituents of plant sera. Rubber exists as high polymer in latex at tapping; in mature trees tapped for the first time, it is of high molecular weight and is extensively crosslinked. In normal commercial practice, when latex is withdrawn as fast as rubber is sythesized by the tree, rubber is essentially all linear high polymer of average molecular weight 105 to 106. As soon as a tree is tapped the latex begins to change. In the short period between tapping and coagulation the changes are small and not usually significant when latex is used for the production of dry rubber. Changes in preserved latex continue over a long time and are significant in its use. Latex of commerce is preserved with ammonia, which serves the dual function of being toxic and controlling pH in a range where latex stability is high. It is sometimes supplemented with another biocide because of the desire to keep ammonia level as low as possible for the convenience of the final user.


2016 ◽  
Vol 83 (1) ◽  
Author(s):  
. Siswanto

AbstrakLateks alam maupun produk jadi yang berasal dari karet alam diketahui mengandung protein alergen. Namun demikian identifikasi jenis protein allergen belum banyak dilaporkan. Penelitian ini bertujuan untuk mendeteksi protein alergen dari sarung tangan dan lateks karet alam menggunakan metode immuno-chemiluminescense. Protein di-ekstrak dari tiga fraksi sentrifugasi lateks (serum B, serum C dan partikel karet) serta tujuh jenis sarung tangan komersial, kemudian dipisahkan berdasarkan berat molekulnya melalui Gel elektroforesis 1-D (SDS PAGE) dan 2-D. Selanjutnya untuk deteksi protein allergen secara immuno-chemiluminescense dilaku-kan imunobloting menggunakan serum Ig_E tiga pasien yang terbukti positif alergi terhadap protein asal sarung tangan lateks, kemudian diwarnai dengan Sypro Ruby protein blot fluorescence. Hasil penelitian menunjukkan bahwa  berdasarkan hasil analisis Western blot one-DE sampel protein lateks menggunakan serum tiga orang tenaga medis yang terbukti positif alergi terhadap protein lateks, maka dapat diidentifikasi 14 jenis protein alergen pada sarung tangan lateks, empat diantaranya merupakan pita major yaitu Berat Molekul (BM) 35, 38, 46 dan 56 kDa. Protein allergen pada sarung tangan tersebut kemungkinan berasal dari bagian C-serum terutama protein  BM 46 dan 56 kDa ataupun campuran antara C-serum dan B-serum dari lateks karet alam. Hal ini dibuktikan bahwa dari sampel C-serum lateks dapat teridentifikasi 12 protein alergen,  empat diantaranya merupakan pita major yaitu BM 42, 46, 51 dan        56 kDa. Sedangkan dari sampel B-serum teridenti-fikasi tiga pita major dengan BM 14, 16 and 51 kDa. Hasil analisis Western blot 2-DE ekstrak protein sarung tangan menggunakan serum tiga orang tenaga medis yang terbukti positif alergi terhadap protein lateks, maka dapat diidentifikasi 12 - 13 spot protein alergen dengan pI at 4.0 to 7.0 dan yang paling dominan adalah dengan BM 23, 35, 38, 42, 45, 46 kDa.Abstract  Natural rubber latex and finished products derived from natural rubber is known to contain allergenic proteins. Nevertheless identification of allergenic protein has not been widely reported. This study aims to detect the protein allergens from the glove of hands and natural rubber latex using immuno-chemiluminescense. Proteins extracted from the latex centrifugation three fractions (serum B, serum C and rubber particles) as well as seven types of commercial gloves, then separated by molecular weight through 1-D gel electrophoresis (SDS PAGE) and 2-D. Furthermore, for the detection of allergen proteins in immuno-chemiluminescense performed immunoblotting using the serum IgE three patients who tested positive for allergy to latex gloves native protein, and then stained with fluorescence Sypro Ruby protein blot. The results showed that based on the results of Western blot analysis of one-DE latex proteins using serum samples three medical personnels who tested positive for allergy to latex proteins, we can identify 14 types of protein allergens in latex gloves, four of which are major bands that having Molecular Weight (MW) 35, 38, 46 and 56 kDa. Protein allergen on the gloves are likely to come from the C-serum protein mainly MW 46 and 56 kDa, or a mixture of C-serum and B-serum of natural rubber latex. It was proved that from C-serum samples could be identified as many as 12 protein latex allergens, four of which were major bands that MW 42, 46, 51 and 56 kDa. While the B-serum samples identified three major bands with MW 14, 16 and 51 kDa. Results of Western blot analysis of 2-DE protein extracts glove using the serum three medical personnel who tested positive for allergy to latex proteins, it could be identified 12-13 allergen protein spot with pI at 4.0 to 7.0 and most dominant is the MW 23, 35, 38, 42, 45, 46kDa.


1998 ◽  
Vol 71 (4) ◽  
pp. 795-802 ◽  
Author(s):  
Jitladda Tangpakdee ◽  
Megumi Mizokoshi ◽  
Akiko Endo ◽  
Yasuyuki Tanaka

Abstract Low molecular-weight natural rubber (LNR) and LNR latex was prepared by oxidative degradation of de-proteinized natural rubber (DPNR) latex in the presence of 1 phr of K2S2O8 and 15 phr of propanal, by shaking at 60 °C. The intrinsic viscosity [η] of DPNR with only K2S2O8 decreased from 7.2 to 5.5 after 2 h and then increased to 6.5 after 3 h. By the addition of propanal, DPNR showed a significant decrease in the [η] value of LNR with [η] of about 0.5 after 5 h of the reaction, while rubber from high-ammonia natural rubber (HANR) latex showed a slight decrease in [η]. The concentration of latex and the kind of surfactant used for stabilizing the latex had little effect on the degradation rate of DPNR latex. The LNR latex is stable as the latex form and the dried rubber coagulated from latex is transparent and colorless. The LNR was a telechelic polymer containing aldehyde and ketone groups at both terminals as determined by NMR and molecular weight analyses.


2015 ◽  
Vol 1134 ◽  
pp. 236-242 ◽  
Author(s):  
Roslim Ramli ◽  
Jefri Jaapar ◽  
Manroshan Singh Jaswan Singh ◽  
Siti Noor Suzila Maqsood Ul Haque ◽  
Amir Hashim Md Yatim

Natural rubber latex is the material of choice for the fabrication of thin elastic films in many products such as gloves and condoms owing to its high strength, elasticity, comfort in use, good barrier properties and ‘green image’ [1, 2]. This unique combination of characteristics has its origins in the intrinsic properties of the crosslinked polymer network within the rubber matrix. The crosslinking of rubber hydrocarbon chains by free radicals generated from peroxide has been discovered for many years [3]. In peroxide crosslinking reactions, organic peroxide decomposes to produce reactive free radicals that will react to release hydrogen ions from the carbon hydrogen in the polymer chain, encouraging formation of free radicals on the rubber molecular chains. As the free radicals react with the polymer chains, the carbon hydrogen in the chains act as reactive centre that combines with centres of other rubber chains to form a network of carbon to carbon bonds which serve as crosslinks [3, 4].


2005 ◽  
Vol 78 (4) ◽  
pp. 597-605 ◽  
Author(s):  
Jitladdat Sakdapipanich ◽  
Patjaree Suksawad ◽  
Kittipong Insom ◽  
Seiichi Kawahara

Abstract Natural rubber (NR) is a high molecular weight (MW) hydrophobic polymer, which can not be easily dissolved in several kinds of solvents, leading to the limitation of usage. NR latex containing low MW and reactive-terminal groups is another interesting form to extend the applications of NR. In this study, a photochemical degradation of NR using H2O2, nanometric TiO2 film and UV irradiation was applied to prepare the hydroxylated low MW NR (LNR). A solid nanometric TiO2 film prepared from titanium solution was applied in the present work. The photosensitivity of the self-assembled TiO2 film was determined by the decomposition rate of methylene blue stock solution using UV/VIS spectrophotometer. The effect of type of NR latex used, H2O2, UV light and TiO2 film on the molecular weight reduction was studied, based on change in intrinsic viscosity determined by Ubbelohde solution viscosity. The structural characterization of the resulting LNR was analyzed by FT-IR and NMR techniques. It was found that hydroxylated LNR with number average molecular weight of 1 × 104 g/mol was obtained by UV irradiation (40 W) of deproteinized natural rubber (DPNR) latex (10% DRC) containing 30% w/w H2O2, on a petri dish coated with TiO2 film for 5 hr. The advantage of this method is that the obtained hydroxylated LNR in either latex or dry rubber form is very clean without further purification.


Polymers ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1216 ◽  
Author(s):  
Suhawati Ibrahim ◽  
Nadras Othman ◽  
Srimala Sreekantan ◽  
Kim Tan ◽  
Zairossani Mohd Nor ◽  
...  

Natural rubber is one of the most important renewable biopolymers used in many applications due to its special properties that cannot be easily mimicked by synthetic polymers. To sustain the existence of natural rubber in industries, modifications have been made to its chemical structure from time to time in order to obtain new properties and to enable it to be employed in new applications. The chemical structure of natural rubber can be modified by exposure to ultraviolet light to reduce its molecular weight. Under controlled conditions, the natural rubber chains will be broken by photodegradation to yield low-molecular-weight natural rubber. The aim of this work was to obtain what is known as liquid natural rubber via photodegradation, with titanium dioxide nanocrystals as the catalyst. Titanium dioxide, which was firstly synthesized using the sol–gel method, was confirmed to be in the form of an anatase, with a size of about 10 nm. In this work, the photodegradation was carried out in latex state and yielded low-molecular-weight natural rubber latex of less than 10,000 g/mol. The presence of hydroxyl and carbonyl groups on the liquid natural rubber (LNR) chains was observed, resulting from the breaking of the chains. Scanning electron microscopy of the NR latex particles showed that titanium dioxide nanocrystals were embedded on the latex surface, but then detached during the degradation reaction.


2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Tianming Gao ◽  
Ruihong Xie ◽  
Linghong Zhang ◽  
Hongxing Gui ◽  
Maofang Huang

The aim of this work is to introduce a simple and rapid method for characterizing the molecular weight parameters and other molecular structure parameters of natural rubber (NR) using a rubber process analyzer (RPA). In this work, NR of different molecular weights was prepared by milling. Molecular weight parameters were measured by gel permeation chromatography coupled with laser light scattering (GPC-LLS) for comparison with RPA results. It was verified that increasing of milling time leads to a decrease of the number-average molecular weight (M-n), weight-average molecular weight (M-w), and molecular weight distribution (MWD). The dynamic and rheological properties were evaluated on RPA by tests of strain sweep, frequency sweep, and stress relaxation. These results were used to characterize the average molecular weight, MWD, and viscosity of NR and were found to agree with those from GPC-LLS. This convenient and rapid technology for characterizing NR molecular weight parameters would be especially useful in the elastomer industry.


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