Quantification of Wood Flour and Polypropylene in Chinese Fir/Polypropylene Composites by FTIR

Author

Guang Pu Xue Yu Guang Pu Fen Xi

Guang Pu Xue Yu Guang Pu Fen Xi 2015 Jun;35(6):1546-50

Wan-li Lao, Gai-yun Li, Qun Zhou, Te-fu Qin

The ratio of wood and plastic in Wood Plastic Composites (WPCss) influences quality and price, but traditional thermochemical methods cannot rapidly and accurately quantify the ratio of wood/PP in WPCss. This paper was addressed to investigate the feasibility of quantifying the wood flour content and plastic content in WPCss by Fourier Transform Infrared (FTIR) spectroscopy. With Chinese fir, polypropylene (PP) and other additives as raw materials, 13 WPCs samples with different wood flour contents, ranging from 9.8% to 61.5%, were prepared by modifying wood flour, mixing materials and extrusion pelletizing. The samples were analyzed by FTIR with the KBr pellets technique. The absorption peaks of WPCss at 1059, 1 033 and 1 740 cm(-1) are considered as characteristic of Chinese fir, and the absorption peaks at 1 377, 2 839 and 841 cm(-1) are typical of PP by comparing the spectra of WPCss with that of Chinese fir, PP and other additives. The relationship between the wood flour content, PP content in WPCss and their characteristic IR peaks height ratio was established. The results show that there is a strong linear correlation between the wood flour content in WPCss and I1 059/l 1 377/I1 033, /I1377, R2 are 0.992 and 0.993 respectively; there is a high linear correlation between the PP content in WPCss and I1 377/I1 740, I2 839 /I1 740 R2 are 0.985 and 0.981, respectively. Quantitative methods of the wood flour content and PP content in WPCss by FTIR were developed, the predictive equations of the wood flour content in WPCss are y = 53.297x-9. 107 and y = 55.922x-10.238, the predictive equations of the PP content in WPCss are y = 6.828 5x+5.403 6 and y = 8.719 7x+3.295 8. The results of the accuracy test and precision test show that the method has strong repeatability and high accuracy. The average prediction relative deviations of the wood flour content and PP content in WPCss are about 5%. The prediction accuracy has been improved remarkably, compared to thermochemical methods. More importantly, FTIR is more easy-handing. This experiment may provide a simple, rapid and accurate method for quantification of wood flour and PP in Chinese fir/PP composites.


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The Use of FTIR Coupled with Partial Least Square for Quantitative Analysis of the Main Composition of Bamboo/Polypropylene Composites

Author
Guang Pu Xue Yu Guang Pu Fen Xi 

Guang Pu Xue Yu Guang Pu Fen Xi 2016 Jan;36(1):55-9

Wan-li Lao, Yu-chan He, Gai-yun Li, Qun Zhou

The biomass to plastic ratio in wood plastic composites (WPCs) greatly affects the physical and mechanical properties and price. Fast and accurate evaluation of the biomass to plastic ratio is important for the further development of WPCs. Quantitative analysis of the WPC main composition currently relies primarily on thermo-analytical methods. However, these methods have some inherent disadvantages, including time-consuming, high analytical errors and sophisticated, which severely limits the applications of these techniques. Therefore, in this study, Fourier Transform Infrared (FTIR) spectroscopy in combination with partial least square (PLS) has been used for rapid prediction of bamboo and polypropylene (PP) content in bamboo/PP composites. The bamboo powders were used as filler after being dried at 105 degrees C for 24 h. PP was used as matrix materials, and some chemical regents were used as additives. Then 42 WPC samples with different ratios of bamboo and PP were prepared by the methods of extrusion. FTIR spectral data of 42 WPC samples were collected by means of KBr pellets technique. The model for bamboo and PP content prediction was developed by PLS-2 and full cross validation. Results of internal cross validation showed that the first derivative spectra in the range of 1 800-800 cm(-1) corrected by standard normal variate (SNV) yielded the optimal model. For both bamboo and PP calibration, the coefficients of determination (R2) were 0.955. The standard errors of calibration (SEC) were 1.872 for bamboo content and 1.848 for PP content, respectively. For both bamboo and PP validation, the R2 values were 0.950. The standard errors of cross validation (SECV) were 1.927 for bamboo content and 1.950 for PP content, respectively. And the ratios of performance to deviation (RPD) were 4.45 for both biomass and PP examinations. The results of external validation showed that the relative prediction deviations for both biomass and PP contents were lower than ± 6%. FTIR combined with PLS can be used for rapid and accurate determination of bamboo and PP content in bamboo/PP composites.

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Wood-plastic composites utilizing ionomer capstocks and methods of manufacture

ABSTRACT

An extruded composite adapted for use as a building material includes a core having a base polymer and a natural fiber in a substantially homogeneous mixture and an ionomer capstock. To improve adherence of the ionomer to a base polymer, the ionomer can be mixed with a similar or substantially similar base polymer prior to coextrusion with the core. Additionally, various additives may be mixed with the capstock material to improve visual aesthetics of the product and performance of the building material, especially over time.

DESCRIPTION

WOOD-PLASTIC COMPOSITES UTILIZING IONOMER CAPSTOCKS AND METHODS OF MANUFACTURE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Application Serial No. 61/139,205, filed December 19, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to systems and methods for fabricating extruded wood-plastic composites and, more particularly, to systems for fabricating extruded wood-plastic composites that utilize ionomer cap stocks.

BACKGROUND OF THE INVENTION

[0003] In the past 25 years, a new type of material has entered the plastics products market. Commonly referred to as wood-plastic composites (WPCs), fiber-plastic composites, or plastic composites (PCs), the new materials have been accepted into the building products markets in applications such as outdoor decking and railing, siding, roofing and a variety of other products. The market for the wood-plastic composite has grown and WPCs now are used in automotive applications, as well as in the building products sector of the economy.

[0004] A wood-plastic composite is a blended product of wood, or other natural fibers, and a thermoplastic material. The products can be produced with traditional plastics processes such as extrusion or injection molding. For example, many building products are produced using extrusion processing similar to conventional plastics processing. The wood and plastics materials are blended before or during the extrusion process. The wood-plastic composites often compete with wood in the building products market. The current WPC materials are most often compounds of wood, or natural fibers, and polyethylene, polypropylene, or polyvinyl chloride (PVC). Presently available WPCs, however, suffer from certain drawbacks. For example, if the composite contains too high or too low of a ratio of plastic to wood, the finished product may not have the desired visual appearance or structural performance characteristics. Such products are less desirable in the marketplace. Additionally, WPCs may be expensive to produce, due to the high cost of the thermoplastic materials and other additives used in manufacture.

[0005] Ironically, many consumers expect WPCs to appear similar to wood, but also expect WPCs to perform as a robust plastic compound. To increase performance, manufacturers often incorporate UV stabilizers, antioxidants, biocides, color, fire retardants, or other additives into the WPC formulation. These additives, however, can increase manufacturing costs of the product, even though certain additives provide noticeable benefit only on a limited location on the product (e.g., in the case of UV stabilizers, the benefit only effects the exterior of the product that is exposed to sunlight). To reduce the amount of additives that are incorporated into the product, capstocking is often used. In general, capstocks are coextruded with the core material to form a thin layer of polymer over the core extruded material. Various additives may be incorporated into the capstock, thus reducing the total amount of additives per linear foot of product. These capstocks, however, may suffer from delamination from the underlying WPC and may crack or otherwise fail, causing an unsightly appearance, impaired performance, and consumer dissatisfaction.

[0006] With certain capstocks, to improve adhesion, a discrete tie layer is typically placed between the core material and capstock, but this tie layer can present a number of problems. For example, the bond formed by the tie layer may separate from one or both of the capstock and core material over time, leading to product failure. This may occur because the capstock and core material may expand and contract at different rates, due to differences in material properties, which may cause failure of the bond. Also, water, ice, or other hazards related to installed environmental conditions can still penetrate the capstock layer, for example, via gaps at the edges of discrete capstock sections. Additionally, manufacturing costs of capstocked products utilizing a discrete tie layer tend to be high, since the tie layer must be applied to finished capstock and core materials. 

SUMMARY OF THE INVENTION

[0007] In one aspect, the invention relates to an extruded composite adapted for use as a building material, the extruded composite including a core having a base polymer and a natural fiber in a substantially homogeneous mixture and a capstock having an ionomer. In an embodiment, the base polymer is selected from the group consisting of polypropylene, polyethylene, HDPE, MDPE, LDPE, LLDPE, and combinations thereof. In another embodiment, the natural fiber is selected from the group consisting of wood chips, wood flour, wood flakes, sawdust, flax, jute, hemp, kenaf, rice hulls, abaca, and combinations thereof. In yet another embodiment, the capstock further includes a capstock polymer, wherein the ionomer and the capstock polymer are a substantially homogeneous mixture. In still another embodiment, the base polymer a first polymer and the capstock polymer is the first polymer, which may be HDPE.

[0008] In another embodiment of the above aspect, the capstock further includes an additive. In an embodiment, wherein the additive includes at least one of a colorant, a UV stabilizer, an antioxidant, a biocide, and a fire retardant. In another embodiment, the colorant is a variegated colorant. In yet another embodiment, the core includes about 1% to about 100% base polymer, by weight. In still another embodiment, the core includes about 46% base polymer, by weight.

[0009] In another embodiment of the above aspect, the capstock includes about 1% to about 100% ionomer, by weight; about 20% to about 80% ionomer, by weight; or about Tl 5% ionomer, by weight. In another embodiment, the capstock includes about 0% to about 99% capstock polymer, by weight; about 20% to about 80% capstock polymer, by weight; or about 72.5% capstock polymer, by weight. In yet another embodiment, the capstock has a thickness of about 0.012 inches to about 0.040 inches, or about 0.015 inches to about 0.020 inches. In still another embodiment the capstock is bonded directly to at least one side of the core via coextrusion.

0010] In another aspect, the invention relates to a method of manufacturing an extruded composite adapted for use as a building material, the method including the steps of providing a base polymer, providing a natural fiber, mixing and heating the base polymer and the natural fiber to produce a base mixture including a substantially homogeneous melt blend, providing an ionomer, and coextruding the ionomer onto at least a portion of the base mixture through a die to form an extruded profile. In an embodiment, the method further includes the steps of providing a capstock polymer, and mixing and heating the ionomer and the capstock polymer to produce a capstock mixture having a substantially homogeneous melt blend. In another embodiment, the base polymer is a first polymer and the capstock polymer is the first polymer, which may be selected from the group consisting of polypropylene, polyethylene, HDPE, MDPE, LDPE, LLDPE, and combinations thereof. In one embodiment, the first polymer is HDPE. In yet another embodiment, the method further includes the steps of providing an additive, and mixing and heating the ionomer, the capstock polymer, and the additive to produce a capstock mixture having a substantially homogeneous melt blend. In still another embodiment, the additive is at least one of a colorant, a UV stabilizer, an antioxidant, a biocide, and a fire retardant. In another embodiment, the method further includes the step of cooling the extruded profile, which may include passing the extruded profile through a liquid, which maybe at least one of a water and a coolant.

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http://www.google.com/patents/WO2010071879A2?cl=en

WOOD - PLASTIC COMPOSITES FROM WASTE MATERIALS RESULTED IN THE FURNITURE MANUFACTURING PROCESS

Author

Camelia COŞEREANU; Dumitru LICA (2014)

Publisher: Editura Universitatii Transilvania din Brasov

Journal: Pro Ligno

Languages: English

Types: Article

Subjects:  wood-plastic, waste materials, ABS, planer shavings, particle size distribution, Forestry, SD1-669.5, Agriculture, S

The paper presents the application of waste materials resulted in the furniture manufacturing process as components for wood-plastic composites. The composites are produced from industrial byproducts, such as shavings and ABS (acrylonitrile butadiene styrene), without coupling agent. The two components are derived from industrial processes of furniture manufacturing: the first one consists of wood residues resulted from planing machine as planer shavings, and the second one from ABS edge banding operation. A wide array of mixtures varying from 100% ABS to 50% ABS: 50% shavings were used to produce eight variants of boards. Density was determined for each board and the method for the determination of ABS particle size distribution by oscillating screen method using sieve apertures up to 4mm was also applied, in order to establish the particle fractions and the distribution of their sizes. Based on ABS properties, several technologies of manufacturing wood-plastic composites from the waste materials were tested and one of them was selected. The results of the first stage analysis, when the physical integrity and the compactness of the panels’ structures were tested, have shown that a maximum proportion of 30% of wood shavings is accepted in the mixture. On the other hand, the low density of the boards and their porous structure recommend further investigations for thermal and sound insulation applications

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Investigating the possibility of using new wood-based composite materials in staircase design

Author

Jokinen, Tatu (2014)

Languages: English

Types: Master thesis

Subjects:  staircase, HPL, MDF, plywood

Wooden staircases are made with similar solid wood design decades. Wood-based composites have replaced most of solid wood in furniture but not in the staircases. Wood-based composites have several problems that need to be solved before they can be used for manufacturing staircase. Few of the using possibilities are investigated in thesis. This thesis has two focus areas of how to increasing use of wood-based composites in staircases. First, wood-based composite materials are increasing surface coating possibilities. One suitable coating is High pressure laminates. That would need wood-based composite board for substrate. MDF is most suitable material for substrate. Also other substrate possibilities are investigated. Second focus area is possibility to make curved stair parts for using thermoformable plywood (UPM Grada). Inside or outside stringers can be curved in winding stairs. Those stringers are very slow to manufacture in traditional way for using solid wood. Bendable plywood gives possibility to machine connections before bending. Study is made by desktop researching based on literature and then small scale prototype manufacturing for proving ideas. Result for investigation is that MDF coated with HPL can be made with reasonable price. Surface properties of the HPL are better than painted solid wood. Tread would need stronger floor grade laminate for archive long lifetime. Problem is that it would not suit all stairwell spaces as available board size will be limiting stringer length. Other problem is deflection of tread without riser. Grada can be bended in stringer thickness (30mm, three 10mm board glued together before forming) and use for inner corner stringer. Connection mortising for tread can be made before forming and small finishing is needed after forming. Disadvantage is slow developing process in forming mould manufacturing, that limiting possibility of customizing product for different projects. Puuportaita on tehty samalla tyylillä pitkään. Puupohjaiset komposiittilevyt ovat korvanneet massivipuun useissa kalusteissa kuin portaissa. Puupohjaisilla komposiittilevyillä on useita ongelmia, jotka pitäisi ratkaista ennen niiden käyttöä portaiden valmistuksessa. Tässä työssä tutkitaan muutamaa käyttömahdollisuutta. Tässä työssä on kaksi tutkimusaluetta siitä, kuinka portaissa voidaan lisätä puupohjaisten komposiittilevyjen käyttöä. Puupohjaiset komposiittilevyt lisäävät pinnoitusmahdollisuuksia. Yksi käyttökelpoinen pinnoite on korkeapainelaminaatti (HPL), joka tarvitsee puupohjaisen komposiittilevyn pohjalevyksi. MDF on soveltuvin siihen tarkoitukseen. Myös muut pohjalevy vaihtoehto mahdollisuudet on tutkittu. Toisessa tutkimusalueessa tutkitaan mahdollisuutta tehdä kaarevia portaanosia käyttämällä kuumamuotoiltavaa vaneria (UPM Grada). Sisä- ja ulkoreisipuut voivat olla kaarevat kiertävissä portaissa. Kaarevat reisipuut ovat hitaat valmistaa perinteisesti massiivipuusta. Taivutettava vaneri antaa mahdollisuuden tehdä liitoskoneistukset ennen taivutusta. Tutkimus on tehty kirjallisuuteen pohjautuvana työpöytätutkimuksena, jonka jälkeen pienen mittakaavan prototyyppi valmistettiin idean varmistamiseksi. Tuloksena tutkimuksesta on se, että korkeapainelaminaatilla pinnoitettu MDF voidaan tehdä kohtuullisella hinnalla. Pinnanominaisuudet ovat paremmat korkeapainelaminaatilla kuin maalatulla männyllä. Korkean käyttöiän saavuttamiseksi askelmat tarvitsevat vahvemman lattialaadun laminaatin. Ongelma laminaateissa on, etteivät ne sovellu kaikkiin porrastiloihin, koska saatavilla oleva levykoko rajoittaa reisipuun pituutta. Toinen ongelma on askelmien joustaminen ilman potkulevyjä. Gradaa voidaan taivuttaa reisipuun paksuudessa (30 mm, kolme 10 mm levyä liimattu yhteen ennen muotoilua) ja käyttää sisäkulman reisipuuna. Liitosjyrsinnät askelmille voidaan tehdä ennen muotoilua ja muotoilun jälkeen tarvitaan pientä viimeistelyä. Haittana on taivutusmuotin hidas kehittämisprosessi, joka rajoittaa mahdollisuutta räätälöidä tuotetta eri projekteihin

For further details log on website :
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Investigating the possibility of using new wood-based composite materials in staircase design

Published Date
Permanent link to this item:  http://urn.fi/URN:NBN:fi:aalto-201412113218

Title:	Investigating the possibility of using new wood-based composite materials in staircase design Tutkimus puupohjaisten komposiittilevyjen käyttömahdollisuudesta porrasrakenteessa
Author(s):	Jokinen, Tatu
Date:	2014-12-02
Language:	en
Pages:	86
Major/Subject:	Puutuotekniikka
Supervising professor(s):	Hughes, Mark
Thesis advisor(s):	Tukiainen, Pekka
Keywords:	staircase, HPL, MDF, plywood
Location:	PK  |  Location information (printed version)
» Show full item record
Abstract

Wooden staircases are made with similar solid wood design decades. Wood-based composites have replaced most of solid wood in furniture but not in the staircases. Wood-based composites have several problems that need to be solved before they can be used for manufacturing staircase. Few of the using possibilities are investigated in thesis.

This thesis has two focus areas of how to increasing use of wood-based composites in staircases. First, wood-based composite materials are increasing surface coating possibilities. One suitable coating is High pressure laminates. That would need wood-based composite board for substrate. MDF is most suitable material for substrate. Also other substrate possibilities are investigated. Second focus area is possibility to make curved stair parts for using thermoformable plywood (UPM Grada). Inside or outside stringers can be curved in winding stairs. Those stringers are very slow to manufacture in traditional way for using solid wood. Bendable plywood gives possibility to machine connections before bending. Study is made by desktop researching based on literature and then small scale prototype manufacturing for proving ideas.

Result for investigation is that MDF coated with HPL can be made with reasonable price. Surface properties of the HPL are better than painted solid wood. Tread would need stronger floor grade laminate for archive long lifetime. Problem is that it would not suit all stairwell spaces as available board size will be limiting stringer length. Other problem is deflection of tread without riser. Grada can be bended in stringer thickness (30mm, three 10mm board glued together before forming) and use for inner corner stringer. Connection mortising for tread can be made before forming and small finishing is needed after forming. Disadvantage is slow developing process in forming mould manufacturing, that limiting possibility of customizing product for different projects.

Puuportaita on tehty samalla tyylillä pitkään. Puupohjaiset komposiittilevyt ovat korvanneet massivipuun useissa kalusteissa kuin portaissa. Puupohjaisilla komposiittilevyillä on useita ongelmia, jotka pitäisi ratkaista ennen niiden käyttöä portaiden valmistuksessa. Tässä työssä tutkitaan muutamaa käyttömahdollisuutta.

Tässä työssä on kaksi tutkimusaluetta siitä, kuinka portaissa voidaan lisätä puupohjaisten komposiittilevyjen käyttöä.

Puupohjaiset komposiittilevyt lisäävät pinnoitusmahdollisuuksia. Yksi käyttökelpoinen pinnoite on korkeapainelaminaatti (HPL), joka tarvitsee puupohjaisen komposiittilevyn pohjalevyksi. MDF on soveltuvin siihen tarkoitukseen. Myös muut pohjalevy vaihtoehto mahdollisuudet on tutkittu. Toisessa tutkimusalueessa tutkitaan mahdollisuutta tehdä kaarevia portaanosia käyttämällä kuumamuotoiltavaa vaneria (UPM Grada). Sisä- ja ulkoreisipuut voivat olla kaarevat kiertävissä portaissa. Kaarevat reisipuut ovat hitaat valmistaa perinteisesti massiivipuusta. Taivutettava vaneri antaa mahdollisuuden tehdä liitoskoneistukset ennen taivutusta. Tutkimus on tehty kirjallisuuteen pohjautuvana työpöytätutkimuksena, jonka jälkeen pienen mittakaavan prototyyppi valmistettiin idean varmistamiseksi.

Tuloksena tutkimuksesta on se, että korkeapainelaminaatilla pinnoitettu MDF voidaan tehdä kohtuullisella hinnalla. Pinnanominaisuudet ovat paremmat korkeapainelaminaatilla kuin maalatulla männyllä. Korkean käyttöiän saavuttamiseksi askelmat tarvitsevat vahvemman lattialaadun laminaatin. Ongelma laminaateissa on, etteivät ne sovellu kaikkiin porrastiloihin, koska saatavilla oleva levykoko rajoittaa reisipuun pituutta. Toinen ongelma on askelmien joustaminen ilman potkulevyjä. Gradaa voidaan taivuttaa reisipuun paksuudessa (30 mm, kolme 10 mm levyä liimattu yhteen ennen muotoilua) ja käyttää sisäkulman reisipuuna. Liitosjyrsinnät askelmille voidaan tehdä ennen muotoilua ja muotoilun jälkeen tarvitaan pientä viimeistelyä. Haittana on taivutusmuotin hidas kehittämisprosessi, joka rajoittaa mahdollisuutta räätälöidä tuotetta eri projekteihin.

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Radiation processed composite materials of wood and elastic polyester resins

Published Date
Proceedings of the 5th Tihany symposium on radiation chemistry held at Siofok, 19-24 Sep 1982. 
Vols. 1,2

[en]

 The radiation polymerization of multifunctional unsaturated polyester-monomer mixtures in wood forms interpenetrating network system. The mechanical resistance (compression, abrasion, hardness, etc.) of these composite materials are generally well over the original wood, however the impact strength is almost the same or even reduced, in comparison to the wood itself. An attempt is made using elastic polyester resins to produced wood-polyester composite materials with improved modulus of elasticity and impact properties. For the impregnation of European beech wood two types of elastic unsaturated polyester resins were used. The exothermic effect of radiation copolymerization of these resins in wood has been measured and the dose rate effects as well as hardening dose was determined. Felxural strength and impact properties were examined. Elastic unsaturated polyester resins improved the impact strength of wood composite materials. (author)

Primary Subject

RADIATION CHEMISTRY, RADIOCHEMISTRY AND NUCLEAR CHEMISTRY (B1400)
Secondary SubjectISOTOPES AND RADIATION SOURCES (D2300)
SourceDobo, Janos; Hedvig, Peter; Schiller, Robert (eds.); Mueszaki es Termeszettudomanyi Egyesueletek Szoevetsege, Budapest (Hungary); International Atomic Energy Agency, Vienna (Austria); v. 2 p. 793-798; ISBN 963 05 3429 0; ; 1983; v. 2 p. 793-798; Akademiai Kiado; Budapest (Hungary); 5. Tihany symposium on radiation chemistry; Siofok (Hungary); 19-24 Sep 1982; 5 refs.
Record TypeBook
Country of publicationHungary
Descriptors (DEI)CHEMICAL RADIATION EFFECTS, COPOLYMERIZATION, DOSE RATES, IMPREGNATION, MECHANICAL PROPERTIES, POLYESTERS, POLYMERIZATION, RADIATION HARDENING, WOOD, WOOD-PLASTIC COMPOSITES
Descriptors (DEC)CHEMICAL REACTIONS, COMPOSITE MATERIALS, ESTERS, HARDENING, MATERIALS, ORGANIC COMPOUNDS, ORGANIC POLYMERS, PHYSICAL RADIATION EFFECTS, POLYMERS, RADIATION EFFECTS
Reference Number16017178
Related Record15006540
Publication Year1983
INIS Volume16
INIS Issue05

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Effects of formulation variables on surface properties of wood plastic composites

Published Date

Article (PDF Available) in Composites Part B Engineering 43(2) · March 2012 with 135 Reads

DOI: 10.1016/j.compositesb.2011.07.011

• 

  1st Nadir Ayrilmis

  36.45 · Istanbul University
• 

  2nd Jan Thore Benthien

  17.72 · Thünen Institute
• 

  3rd Heiko Thoemen

Abstract

Degree of surface quality of wood plastic composites (WPCs) is a function of both raw material characteristics and the manufacturing variables. The WPC panels comprised of different panel densities (800, 950, 1000, and 1080kg/m3), wood flour contents (50, 60, 70, and 80wt.%), wood flour sizes (1mm), and hot-pressing temperatures (190 and 210°C) were manufactured using a dry blend/flat-pressing method under laboratory conditions. The surface smoothness of the WPC panels improved with increasing WPC density, plastic content, and hot-pressing temperature while it deteriorated with increasing wood flour size. The reduction in the particle size of the WF resulted in a more compact structure on the WPC surface. In general, the wettability of the samples increased by increasing surface roughness.

For further details log on website :
https://www.researchgate.net/publication/251669990_Effects_of_formulation_variables_on_surface_properties_of_wood_plastic_composites

Multiresponse optimization based on statistical response surface methodology and desirability function for the production of particleboard

Published Date

Article (PDF Available) in Composites Part B Engineering 43(3):861–868 · April 2012 with 157 Reads

DOI: 10.1016/j.compositesb.2011.11.033

Author 

1st Md. Azharul Islam

25.29 · Khulna University

2nd Md. Rabiul Alam

6.78 · Khulna University

3rd Md. Obaidullah Hannan

Abstract

It is very difficult to determine the actual level of process parameters responsible for the quality production of particleboard due to the high degree of process variable interactions and lack of robust methodology for optimization. In this study, an attempt was made to optimize the process parameters of particleboard production by using multi-response optimization process. Plackett–Burman factorial design was first employed to eliminate some factors from selected seven important parameters: flake thickness, flake length, dried chips moisture content (MC%), amount of adhesive, pressing time, pressure, and press temperature. By using this screening procedure, three important factors: flake thickness, dried chips moisture content and press temperature were found to have significant effect on particleboard properties. Afterwards, Box–Behnken design was performed as response surface methodology (RSM) with desirability functions to attain the optimal flake thickness, MC% and press temperature that affect modulus of rapture (MOR) and modulus of elasticity (MOE) of particleboard production. The optimized parameters for maximum MOR and MOE determined were found to be: flake thickness, 0.15 mm; press temperature, 182 °C; and dried chip MC% 3.5. Finally, a confirmation study was execu

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Melt processing and properties of linear low density polyethylene-graphene nanoplatelet composites

Published Date

doi:10.1016/j.vacuum.2016.04.022

Open Access, Creative Commons license

Author 

P. Noorunnisa Khanam ^a

M.A. AlMaadeed ^a,b,,

M. Ouederni ^c

Eileen Harkin-Jones ^d

Beatriz Mayoral ^e

Andrew Hamilton ^e

Dan Sun ^e

• aCenter for Advanced Materials, Qatar University, 2713, Doha, Qatar
• bMaterials Science and Technology Program, Qatar University, 2713, Doha, Qatar
• cQatar Petrochemical Company, Qatar
• dSchool of Engineering, University of Ulster, UK
• eSchool of Mechanical & Aerospace Engineering, Queen's University Belfast, UK

Received 5 January 2016. Revised 5 March 2016. Accepted 21 April 2016. Available online 22 April 2016.

Highlights

• •
  LLDPE/GNPs composites were prepared by melt processing.
• •
  Effect of extruder screw speeds, feeder speeds and GNPs wt% on mechanical, thermal and electrical properties was studied.
• •
  High screw and feeder speeds enhanced mechanical, thermal and electrical properties of the composites.

Abstract 

Composites of Linear Low Density Polyethylene (LLDPE) and Graphene Nanoplatelets (GNPs) were processed using a twin screw extruder under different extrusion conditions. The effects of screw speed, feeder speed and GNP content on the electrical, thermal and mechanical properties of composites were investigated. The inclusion of GNPs in the matrix improved the thermal stability and conductivity by 2.7% and 43%, respectively. The electrical conductivity improved from 10⁻¹¹ to 10⁻⁵ S/m at 150 rpm due to the high thermal stability of the GNPs and the formation of phonon and charge carrier networks in the polymer matrix. Higher extruder speeds result in a better distribution of the GNPs in the matrix and a significant increase in thermal stability and thermal conductivity. However, this effect is not significant for the electrical conductivity and tensile strength. The addition of GNPs increased the viscosity of the polymer, which will lead to higher processing power requirements. Increasing the extruder speed led to a reduction in viscosity, which is due to thermal degradation and/or chain scission. Thus, while high speeds result in better dispersions, the speed needs to be optimized to prevent detrimental impacts on the properties.

Keywords

Melt processing

Graphene nanoplatelets

Mechanical properties

Electrical properties

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1 Introduction

Graphene which is a two-dimensional, single-layer of sp2 hybridized carbon atoms, has attracted researchers due to its excellent properties, such as high electrical conductivity, high thermal stability and high mechanical strength. These excellent properties along with its simple manufacture and functionalization makes graphene an ideal to be added in different functional materials. Graphene and graphene based materials have already been used in many applications such as electronic and electrical field [1] and [2].

Industrial and academic are highly interested in graphene and graphene polymer nano composites [3]. Graphene has a higher surface-to-volume ratio compared to carbon nanotubes (CNTs) as the inner surface of the nanotubes is not accessible to the polymer molecules [4] and [5], which makes graphene more favorable than CNTs for optimizing the required function or application such as the modification in the electrical, thermal, mechanical and microwave absorption properties. Another advantage is that graphene has lower cost [4], [5] and [6] choice compared to CNTs because it can be easily made from graphite in large quantities [5]. In the literature, researchers have used various polymers as matrices to prepare the required modified graphene/polymer composites [5], the mechanical, electrical [7], [8] and [9], thermal [9], and various other properties [10] have been extensively investigated.

Many methods described in literature about the preparation of graphene such as exfoliation of the graphite by micromechanical methods, chemical methods [4] and [5] or chemical vapor deposition.

Rouff and coworkers [11] and [12] synthesized graphene from graphite. The reduction of the GO was performed using hydrazine hydrate (chemical method). Single sheets of graphene were prepared via oxidation and thermal expansion of graphite [13]. The synthesis of graphene films with thicknesses of a few layers via CVD was reported by Somani et al. [14], where camphor was used as the precursor on Ni foils. Graphene was prepared via the exfoliation of graphite in aromatic solutions. Grandthys et al. [15] induced the epitaxial growth of graphene on a transition metal using chemical vapor deposition and liquid phase deposition. A high yield of graphene was produced via the liquid-phase exfoliation of graphite [16].

Graphene nanoplatelets (GNPs) are platelet-like graphite nanocrystals containing multiple graphene layers. Maximum stress transfer from the polymer to the filler is achieved with the high interaction zone between the polymer and the filler which can increase the mechanical properties of the composites. Due to the ultra-high aspect ratio (600–10,000), properties of GNPs can have better filler than other fillers in polymer composites. The planar structure of the GNPs provides a 2D path for phonon transport, which provides a large surface contact area with the polymer matrix, which can increase the thermal conductivity of the composite [17]. Common techniques to produce GNPs include chemical reduction of homogeneous colloidal suspension of single layered graphene oxide [18] and by exfoliation of natural graphite flakes by oxidation reaction [19]. Some of researchers prepared GNPs from natural graphite via exfoliation and intercalation with tetra alkyl ammonium bromide [20]. Others such as Cameron Derry et. Al [21]. prepared the GNPs by electric heating acid method.

The aggregation and stacking of graphene nanoplatelets limited the performance of graphene polymer nanocomposites. Because the aggregated GNPs properties can be similar to the graphite with its limited specific surface area. The performance of GNPs can be reduced due to aggregation, which should be addressed as an issue if the potential of GNPs as reinforcing agents is to be realized. Therefore, the objective of this current research is to determine how compounding conditions can influence dispersion and subsequent composite properties.

Linear Low Density Polyethylene (LLDPE) was chosen as the matrix material in this research due to its significant commercial importance. LLDPE has grown most rapidly within the PE (polyethylene) family due to its good balance of mechanical properties and processability compared to other types of PE [22]. Electrically conductive PE based composite materials can be used as electromagnetic-reflective materials, as well as in high voltage cables.

As stated earlier, it is important to achieve good dispersion of a filler material to realize enhancement of the mechanical properties. What is not so clear is how the dispersion state influences the electrical conductivity, and the optimum dispersion state is currently being debated in the literature.

This work attempts to advance knowledge in the area of melt-processed GNP polymer composites by investigating the influence of the compounding conditions on the electrical, thermal and mechanical properties of the GNP/LLDPE composites.

2 Experimental

2.1 Materials

2.1.1 Polymer matrix

LLDPE (MFI = 1 g/cm³) in powder form was kindly supplied by Qatar Petrochemical Company (QAPCO), Qatar. Prior to the melt processing, 0.4 g of phenolic stabilizer was added for each 1 kg of LLDPE to protect it from degradation during the high temperature processing.

2.1.2 Filler

Graphene nanoplatelets of grade C (C-GNPs) were purchased from XG sciences. Grade C particles have diameter of less than 2 μm. They consist of aggregates of sub-micron platelets. Particle thickness of C-GNPs is 1–5 nm which depends on the surface area. Average Surface area of Grade C particles is 500 m²/g.

2.2 Preparation of LLDPE/graphene nano composites pellets

LLDPE composites reinforced with 1,2,4,6,8 and 10 wt% ‘C’ grade graphene were processed using a five-stage Brabender twin screw extruder with three different screw/feeder speeds as shown in Fig. 1. The temperatures of the processing zones were in the range of 190–230 °C. The processing zone temperatures were chosen according to previous reports [23]. Table 1 lists the experimental sets that were executed The polymer/C-GNPs mixtures were fed into the hopper and extruded into strands, which were then cooled in water and granulated into pellets. Fig. 1 shows a schematic diagram of the twin screw extruder. The extruded pellets were subsequently hot pressed into plaques via compression molding. They were held for 20 min in the press at a temperature of 170 °C [24] before a pressure of 165.5 MPa was applied for 20 min. The plaques were then cooled at room temperature. The plaque dimensions were 5 cm length × 5 cm width × 0.5 cm thick.

Fig. 1. Schematic diagram of GNPs nanocomposites processing.

Table 1. List of prepared samples with different screw speeds and different feeder speeds.

S.No.	Extruder speed (rpm)	Feeder (kg/h)	% of graphene nanoplateletes	% of LLDPE
1	50	50	0	100
2	100	100	0	100
3	150	150	0	100
4	50	50	1	99
5	50	50	2	98
6	50	50	4	96
7	50	50	6	94
8	50	50	8	92
9	50	50	10	90
10	100	100	1	99
11	100	100	2	98
12	100	100	4	96
13	100	100	6	94
14	100	100	8	92
15	100	100	10	90
16	150	150	1	99
17	150	150	2	98
18	150	150	4	96
19	150	150	6	94
20	150	150	8	92
21	150	150	10	90

2.3 Characterizations

2.3.1 Scanning electron microscopy (SEM)

Philips EDX scanning electron microscope (SEM) was used to analyze the morphological analysis. To study the graphene nanoplatelets morphology, 10 mg of the sheets was dispersed in 10 ml of acetone, and the solution was sonicated for 30 min. Cross sections of the composite samples after tensile testing was studied by using SEM which investigate the dispersion of the graphene nanoplatelets in the polymer matrix. SEM was used (3 KV) with high vacuum and different magnifications. The images were collected without coating the samples.

2.3.2 Transmission electron microscopy (TEM)

The C-GNPs were mixed with acetone and sonicated for 30 min. A drop was coated onto a copper grid and placed in a high resolution transmission electron microscope (FEI TECNAI TF 20, 200 kV), which was used to explore the morphology of the GNPs.

2.3.3 Thermal properties

2.3.3.1 Thermogravimetric analysis (TGA)

The thermogravimetric analysis (TGA) of the C-GNPs/LLDPE composites was conducted using a Perkin Elmer 6 under a nitrogen atmosphere from ambient temperature to 700 °C at a heating rate of 10 °C/min. The pellets were heated under nitrogen atmosphere.

2.3.4 Electrical conductivity

A Keithley electrometer (Model 2400) was used to measure the electrical conductivity using the 4 point probe method. Compression molded samples were used in this test. The upper and lower surfaces of the 5 cm × 5 cm plaques were coated with a conducting silver paint to ensure intimate contact between the composite surfaces and electrodes. The electrical conductivity (σ) of the sheet was calculated according to the following formula:

where t and A are the thickness of the sheet and effective area of the measuring electrodes, respectively, and R is the resistance of the sample.

2.3.5 Thermal conductivity

The thermal conductivities of the C-GNPs/LLDPE composites were measured using a Hot Disk (Sweden TPS 2500S instrument). The sample dimensions were 5 cm × 2.5 cm with thicknesses of 0.5 cm.

2.3.6 Mechanical testing

The tensile properties of the LLDPE/C-GNPs composites were measured using a universal tensile testing machine at room temperature according to ASTM D638-10. Five samples were tested for each composition, and the average value is reported.

2.3.7 Melt flow index

The melt flow index was measured using a Melt Flow Indexer LMI 4004 machine according to ASTM D1238-10.

3 Results and discussion

3.1 SEM and TEM analysis of graphene nanoplatelets

The morphology of the C-grade graphene nanoplatelets was examined using SEM and TEM at different magnifications. SEM micrographs of the C-GNPs powder are presented in Fig. 2(a), and they show that the C-GNPs were in an agglomerated state.

Fig. 2. (a) and (b) SEM images of graphene nanoplatelet powder and (b) sonicated graphene Nanoplatelet (c) and (d) TEM images of graphene nanoplatelet at different magnifications.

Graphene nanoplatelets that were sonicated in acetone and dried at room temperature are shown in Fig. 2(b). Multiple graphene sheets in folded or stacked configurations are observed in this image.

Fig. 2(c) shows that the graphene sheets were folded or overlapped. A higher magnification TEM image of a graphene sheet is shown in Fig. 2(d). These elongated sheets can help achieve higher conductivities [25] in the polymer compared to spherical or elliptical fillers because they form a better conducting network.

3.2 Thermal properties

3.2.1 TGA

The TGA results are shown in Fig. 3. The results show the changes in the degradation temperatures across all of the samples. LLDPE begins to degrade at a low temperature, whereas degradation of the graphene nanocomposites is delayed to degrade at higher temperatures due to the protection produced by the graphene in the polymer.

Fig. 3. Effect of C-GNPs addition on the degradation temperature of LLDPE at different extruder/feeder speeds of 50, 100 and 150 rpm.

As observed from the curves, the degradation peak temperature increases with increasing filler loading in all cases, suggesting that graphene acts as an effective thermal barrier. The LLDPE nanocomposite with 10 wt% C-GNPs has a higher thermal stability than the rest of the graphene composites. The graphene nanoplatelets prevent the emission of small gaseous molecules, disrupt the oxygen supply during the thermal degradation and cause the formation of charred layers on the surface of the nanocomposite.

Graphene nanoplatelets are likely to act in a similar manner to the addition of nano clays and minerals to polymers [26] and [27], i.e., causing the formation of charred layers on the surfaces of the composite and disrupting the oxygen supply to the material underneath. Similar results were observed by other researchers in the literature. Graphene increased the thermal stability of PHBR matrices [28] and increased the thermal stability of PP [29]. The thermal stability of PS nanoparticles was improved by the addition of graphene and increased with the graphene content [30].

Increasing the extruder speed increases the degradation temperature, which is likely due to better dispersion of the C-GNPs at the higher shear rate, hence the formation of a better barrier layer.

3.3 Electrical conductivity

The electrical conductivities of the C-GNPs/LLDPE composites are shown in Fig. 4(a). The results show a considerable increase in the electrical conductivity as the C-GNP content increases, which is a confirmation of the impact of addition of the carbon family to polymers, as concluded by other studies [28] and [31]. The electrical conductivity of LLDPE is 2.14 × 10⁻¹¹ for 50 rpm, 2.81 × 10⁻¹¹ for 100 rpm and 9.2 × 10⁻¹¹ for 150 rpm. The high electrical conductivity of the C-GNPs converts the LLDPE insulator to an electrical conductor. Schematic diagram for electrical conducting networks in LLDPE/C-GNPs is shown in Fig. 4(b) which describes the mechanism whereby graphene formed a conductive network in nanocomposites. A. S. Luyt et al. [32] observed the same behavior of increasing conductivity for LLDPE after the addition of copper. The GNPs in the LDPE composites extruded at speeds of 50, 100 and 150 rpm have the following values for the 4% GNP content: 9.36 × 10⁻⁰⁸, 2.9 × 10⁻⁰⁸ and 3.94 × 10⁻⁰⁷ S/m respectively. As a comparison, a carbon black (CB) content in HDPE of less than 6% [33] results in a value less than 10⁻⁹ S/m. The conductivity reaches 8.94 × 0⁻⁰⁵ for 10% graphene at 150 rpm in our case.

Fig. 4. (a). Effect of C-GNPs addition on the electrical conductivity of LLDPE/C-GNPs composites at different extruder speeds of 50, 100 and 150 rpm, and (b) Schematic diagram of conductive networks formed by C-GNPs in LLDPE/C-GNPs composites.

In general, the composites made at 150 rpm exhibit a slightly higher electrical conductivity than those made at 50 and 100 rpm, especially at C-GNP concentrations of greater than 4% in the matrix. This result will be shown later in the SEM photos, which shows that, at 4% filler content, the graphene nanoplatelets have good dispersion compared to other wt% of the C-GNPs composites.

Low concentrations and poor dispersion may lower the conductivity at low wt% of C-GNPs, this is also reported by Kim et al. [22] who showed local enhancement of electrical conductivity due to better dispersion of the graphene and the formation of interconnected network in the material. As the amount of C-GNPs in the polymer increases more electron paths in the composite are created.

The composites made at 150 rpm exhibited better electrical conductivities than the samples made at 50 and 100 rpm. The ANOVA tests (which will be discussed later) showed no significant relationship with the speed, even with the high value achieved at 150 rpm. The increase in the electrical conductivity may be attributed to the restriction of the additives in the amorphous parts of the polymer [32]. Increasing the speed of the extruder results in a lower viscosity of the polymer, as shown by the MFR test, and better dispersion of the C-GNPs. Higher speeds and shear rates are expected to cause more homogeneous distribution of the fillers, which cause good transfer of the electrons.

3.4 Thermal conductivity

The thermal conductivities of the C-GNPs/LLDPE composites are shown in Fig. 5. The presence of crystalline C-GNPs is expected to enhance the heat transfer at the interface between the C-GNPs and the LLDPE [17], the thermal conductivity increased with the addition of the C-GNPs (with the increase in the wt%).

Fig. 5. Effect of graphene % on thermal conductivity of LLDPE/C-GNPs composites at different extruder speeds of 50, 100 and 150 rpm.

The extruder speed has a pronounced effect on the thermal conductivities of the composites with the highest speed having the greatest positive effect, which is likely due to a better dispersion of the C-GNPs at the higher shear rates. The C-GNPs form a conductive network in the LLDPE matrix, allowing for increased thermal conductivity in the LLDPE. The poor thermal and electrical conductivities inherent to pure LLDPE are enhanced by adding graphene to the polymer in the LLDPE graphene nanocomposites. Filler loading and dispersion in the LLDPE change the thermal conductivity of the polymer composites. In the range between 1 and 4% wt C-GNPs, the thermal conductivity increases slightly because the amount of C-GNPs form a broken system in the LLDPE matrix. Interfacial thermal resistance between the C-GNPs filler and LLDPE matrix are expected at these low percentages of the additives. As the wt% of the C-GNPs in the polymer matrix increases, the thermal conductivity also increases. Thus, the 10 wt% sample has the highest thermal conductivity out of all of the C-GNPs/LLDPE composites.

Graphene fillers, which have high aspect ratios and high surface area can be arranged in unbroken systems/paths in the polymer matrix and have better enhancement of the thermal transfer [17] and [34]. Phonons are important factors in the heat conduction of the solid materials. Thermal conductivity of LLDPE/C-GNPs composites was increased because of the phonon conduction mechanism. Generally, adding highly conductive fillers to a polymer increases the thermal conductivity of the composites. Thermal conductivity as well as other thermal properties depend on properties of both the additives and the matrix [17] and [35]. At low wt%, the fillers in LLDPE are in isolated states. However, when the filler is greater than the percolation threshold of 4 wt%, the fillers aggregate and can arrange unbroken paths for the thermal conductivity. More increase in the wt% of the fillers, can arrange more paths and increase the network [17] and [36].

3.5 Tensile properties

The tensile strengths of the LLDPE/C-GNPs materials are shown in Fig. 6(a). For the 50 rpm sample, the tensile strength increases by 20.3% at a 4 wt% loading of C-GNPs and then falls off to a value lower than the virgin LLDPE at a loading of 10 wt%. The 100 rpm material increased by 6.8% at 2 wt% loading before falling off to the same level as the 50 rpm material at 10 wt%. At 150 rpm, there is an increase in tensile strength of 47.3% at a loading of 4 wt% C-GNPs.

Fig. 6. (a) Effect of graphene addition on tensile strength of LLDPE/C-GNPs composites at different extruder speeds of 50, 100 and 150 rpm and (b) Schematic diagram of LLDPE/C-GNPs composites at low and high wt% of filler.

The tensile strength then falls off dramatically to the same level as the 50 and 100 rpm materials at 10 wt% loading of C-GNPs. The speed effect analyzed using ANOVA (shown in the last part of this paper) showed that there is no significant effect of the speed on the tensile strength even though a published work showed that an enhancement can be achieved in the tensile properties at fast flow and high shear rates [37] due to a decreased residence time.

It appears that the ability of the extruder to break up agglomeration (Fig. 6(b)) is diminished severely at loadings of C-GNPs greater than 4 wt%. The agglomerates act as stress concentrators and reduce the tensile strength. The main reason for the high tensile strength at 4% of C-GNPs loading is the good dispersion and may also be attributed to the possible ordered C-GNPs distribution in the LLDPE matrix. This ordered distribution will be shown in the SEM micrographs.

SEM images (Fig. 7) are used to clarify the reinforcement mechanism and load transfer from the LLDPE to the graphene. Strengthening mechanism of the nano composites was examined by using SEM images which were taken after fracture from tensile test.

Fig. 7. SEM images of (a) pure LLDPE with 150 rpm speed (b), (c) and (d) corresponds to 1wt% C-GNPs/LLDPE composites at 50,100 and 150 rpm speed respectively; (e), (f) and (g) correspond to 4 wt% of C-GNPs/LLDPE composites at 50,100 and 150 speed respectively; (h), (i) and (j) correspond to 10 wt% of C-GNPs/LLDPE composites at of 50, 100 and 150 rpm respectively.

The distributions for the lower (e.g., 1% of C-GNPs) and higher (10% of C-GNPs) samples are not well dispersed in the matrix, and agglomeration might occur at high concentrations which is possible due to the Vander Waals force of the nano sheets which are slipped during the tensile testing causing the decrease of mechanical properties of the composites. SEM image of low wt% of filler reinforced composites clearly shown that the strong interface between the graphene and the LLDPE polymer which is an indication that tensile load is effectively transferred from the LLDPE to the graphene and also shows the uniform distribution of graphene [38].

The reader should be careful to not confuse the behavior of the electrical conductivity and the tensile strength because agglomeration cannot affect the electrical conductivity if there is at least one cluster of particles formed in the matrix [32] and the electrons can move throughout the medium in a conductive path. Increasing the filler concentration increases the electrical conducting paths in the matrix [39].

3.6 SEM analysis

The SEM micrographs in Fig. 7 illustrate the shape of the samples after the tensile testing. Fig. 7(a) shows the ductility behavior of the pure LLDPE sample at 150 rpm. All speeds have similar ductility behaviors (not shown).

Adding C-GNPs causes the samples to be more brittle as shown in Fig. 7(b)–(j). The SEM photos show the good distribution of the 4% C-GNPs in the matrix at all speeds. This behavior was confirmed by the higher tensile strength results at this content level. The agglomeration for high wt% for fillers was reported elsewhere [40]. Various published work about the good dispersion of lower wt% of the additives in polymer composites were also reported [39], [41] and [42]. The 1% and 10% C-GNP samples have more brittle behaviors as the samples have less stretched endings [43]compared to 4 wt%. Also the distribution is not perfect with more agglomeration after the addition of 10% C-GNPs.

3.7 Melt flow index

Table 2 shows the melt flow rate (MFR) information for all of the samples. The MFR is inversely proportional to the dynamic viscosity [44]. The MFR decreases with the addition of C-GNPs, which is in agreement with the published literature [45] and [46], where the incorporation of rigid fillers into a polymer matrix is shown to limit the molecular mobility and increase the material viscosity. Increasing the extruder's speed causes the MFR to increase, which means a decreased molecular weight. This result is likely due to thermal degradation of the polymer and chain scission [47]. The impact of increasing extruder speed on the flow properties of the composite becomes less pronounced as the graphene loading increases because the high additive loading becomes more dominant as a mobility limiting factor than the speed effect.

Table 2. MFR of GNPs/LLDPE composites with different screw speeds.

Samples	MFR for 50 rpm composites (g/10 m)	MFR for 100 rpm composites (g/10 m)	MFR for 150 rpm composites (g/10 m)
LLDPE	0.61	0.79	0.95
1% GNPCs	0.56	0.75	0.91
2%GNPCs	0.54	0.75	0.86
4%GNPCs	0.52	0.67	0.85
6%GNPCs	0.51	0.57	0.83
8%GNPCs	0.50	0.55	0.65
10%GNPCs	0.50	0.52	0.53

3.8 Analysis of variance (ANOVA)

In this paper, a two factor analysis of variance without replication was used to evaluate the significance of the graphene addition and extruder speed on the properties of the composites. The significance level (α) employed in this investigation is 0.05. The F-tests were performed at a confidence level 95%. The results are shown in Table 3.

Table 3. Two-factor ANOVA without replication on different properties.

Properties	P value (speed)	P value (%of graphene)	F value (speed)	F critical (speed)	F value (%of graphene)	F critical (%of graphene)
Tensile strength	0.13	0.0086	2.36	3.88	5	2.9
Degradation temperature	0.00029	3.4E-10	6.52	3.88	31.78	2.99
Thermal conductivity	0.0019	0.000034	11.04	3.88	16.81	2.99
Electrical conductivity	0.12	0.000462	2.43	3.88	9.9	2.99

Note: F, the F value; P-value, the probability of F value; F-crit, the critical value.

The P-values for the degradation temperature, and thermal conductivity are less than the significance level (0.05) for both the graphene percentage and the speed. The F values are greater than F-critical for the same parameters. Therefore, both the speed and the percentage of added graphene are significant for the above properties.

For the effect of graphene addition on the electrical conductivity and tensile strength, the P-values are less than 0.05, and the F-values are greater than F-critical, which suggests that the addition of graphene has a significant effect on these two properties.

For the speed, the P-values for the tensile strength and electrical conductivity are greater than 0.05, and the F-values are smaller than the values of F-critical. This result show that there is no significant relationship between these two properties and the speed of the extruder.

4 Conclusions

The effects of graphene nanoplatelets and extrusion speed on the physical and mechanical properties of LLDPE were studied. Enhancements of the electrical and thermal properties were achieved as the percentage of added C-GNP increased. The thermal conductivity improved significantly at the highest screw speed of 150 rpm, but the speed is not a significant factor in the electrical conductivity. This improved thermal conductivity result is likely due to the better dispersion of the C-GNPs, which results in the formation of more conductive networks. The thermal stability was also enhanced by the addition of the C-GNPs. The tensile strength increased with the addition of C-GNPs up to a loading of 4 wt%. At loadings greater than 4 wt%, even the highest screw speed was unable to break up the agglomerates, which act as stress concentrators and reduce the mechanical performance. The MFR decreased with increasing C-GNP content and decreased with the extruder speed due degradation of the polymer and chain scission.

Acknowledgments

“This work was made possible by NPRP grant No. NPRP5-039-2-014 from the Qatar National Research Fund (A Member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors”.

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