Chengal (Neobalanocarpus Heimii)

Author
By Jungle Boy

The chengal (Neobalanocarpus heimii) tree is a species of dipterocarp that is endemic to Peninsular Malaysia (not found in Borneo) and famous for its durable timber quality. It is also found in southern Thailand near the border with Malaysia, and has been said to have once occurred in Singapore, before its development. Chengal (or cengal) is a monotypic genus, meaning there is only one species in the genus Neobalanocarpus (that is known so far). The strength and durability of its wood (classified as a heavy hardwood) has meant that chengal is highly sought after during logging operations, and it is sometimes referred to as the Malaysian Teak.

The tree is locally common, but may be absent from other places at the same time. It is believed to be absent from large parts of the National Park (Taman Negara) in Pahang, but fortunately, is found in the Terengganu and Kelantan side of the park. However, chengal can be found growing in most parts of Peninsular Malaysia, albeit as scattered individuals in the rainforest, most of the time. In other conservation areas, chengal can be seen at the Pasoh Forest Reserve in Negeri Sembilan (where it is abundant), and it also occurs within the borders of the Krau Wildlife Reserve in Pahang.

Chengal trees can attain an impressive height of over 60 meters tall, in common with many other dipterocarps.

Another view towards the crown of a large chengal tree.

When conditions are ideal, chengal can sometimes grow in groups, to the near exclusion of other tree species, when it becomes the dominant emergent/main canopy tree. It thrives on well drained soil, from mixed swamp forest all the way up to the hills, under 1000 meters altitude.

Very close to the border of Taman Negara in Terengganu, within the Pasir Raja Forest Reserve, a very large specimen was discovered in 1998 by a forest ranger, and so far, this is the largest recorded chengal tree to date. Called the Chengal Besar (Big Chengal), the tree measures 65 meters in height, with a girth of 16.75 meters, average diameter of 5.33 meters, and an estimated age of more than 1300 years. The Malaysia Book of Records lists it as the largest tree of Malaysia, although I believe there are other equally large, if not larger trees in Malaysia (Sabah and Sarawak included). For example, a very huge Shorea platyclados in Kelantan, is visually larger than the Chengal Besar, although with a smaller measured girth, of around 11-12 meters.

The leaves of chengal, from fresh to decaying. They average about 17-20 cm in length. The leaves have “drip tips” at the end; extensions to help drain off rainwater from the surface of the leaves – a feature of many rainforest trees.

The base of the chengal tree. Chengal trees develop medium sized buttress roots and the thick, dark brown bark is often rather scaly, especially in older trees (some more than others). The “scaly” bark is largely reduced towards the crown of the tree. Very old, huge trees like the Big Chengal do not display such scaly bark.

The resin (damar in Malay) of chengal exudes when the bark is damaged, and hardens afterwards to protect the tree.

In the same Pasir Raja Forest Reserve area, not far from the Chengal Besar, another huge chengal tree was also discovered, although this one is smaller, with a girth of 10.75 meters, diameter of 3.42 meters, and a mere height of 45 meters (likely a fat, stout tree). It is clear that chengal is a tree that commonly achieves large size despite its slow growth rate, with diameters of around 2 meters being quite commonly encountered (so long as the forest is unlogged). Large trees are definitely many hundreds of years old, at least.

Due to being durable and generally termite resistant, the stumps of chengal can persist on for decades in the forest, long after the tree has been felled.

Throughout Peninsular Malaysia’s history, chengal wood was the preferred choice of wood for boatbuilding, railway sleepers, and house/building construction. Due to the value of the timber and the tree getting rare, chengal receives special attention from the Forestry Department, and there is a minimum and maximum cutting limit to chop down this tree. The tree is rightly classified as Vulnerable on the IUCN Red List.

For further information log on website :
https://www.rainforestjournal.com/chengal-neobalanocarpus-heimii/

A walk through the Bukit Nanas Forest Reserve

Author
By Jungle Boy

Bukit Nanas Forest Reserve (now called KL Forest Eco-Park) is a small patch of rainforest sited in the heart of Kuala Lumpur, at the base of the towering KL Tower, one of the tallest telecommunications structures in the world. Unknown to many, it is a small green patch that still preserves many species and features of the original rainforest that covered Kuala Lumpur at one time.

Although largely degraded from its original state, there are still some patches within that already tiny patch of forest that retain their original characteristics. Here the trees still stand tall, cicadas still buzz loudly all day long, and save for the sounds of the traffic outside, you would be forgiven for thinking you’re in the middle of an expansive wilderness.

Nature and human edifice side by side. The Bukit Nanas Forest Reserve (KL Forest Eco-Park) still provides shelter for many trees, plants, and animals right in the heart of Kuala Lumpur city.

Background

Bukit Nanas Forest Reserve covers an area of 9.3 hectares. It was originally gazetted as a forest reserve way back in 1906 with a land area of 17.5 hectares, but since then, a large part has already been taken up for building the KL Tower and other purposes. The forest has long suffered from random logging, encroachment, and even war activities, so it’s quite a surprise to find some trees that appear to be several hundred years old in the forest itself.

Some impressively large trees still remain at Bukit Nanas. It is a relic patch of “primary” rainforest in a large metropolis, one of the few in the world, I believe.

During the early years of Kuala Lumpur’s formation, there were pitched battles between rival clans and warlords, and the forested hill was the site of a fort (nothing remains of it today) in the 19^th century. According to historical accounts, pineapples (“nanas” in Malay) were planted all around the fort to deter attackers, hence the name Bukit Nanas (Pineapple Hill) today.

Back in the early 80s, the hill was the site of a small cable car project, but the whole project was scrapped soon after and the cable car service was shut down and dismantled. The forest has now been officially renamed as the KL Forest Eco-Park, but most KL citizens will still know and call it by its old name.

Trails in Bukit Nanas Forest Reserve

There are several trails that run through the forest reserve, which if seen from the air, is mainly limited to the one side of the hill, with the central portion or highest point taken up by the KL Tower. The official entrance is located near Jalan Raja Chulan, but the easiest way to get to the forest is by taking the Rapid KL LRT and disembarking at the Dang Wangi LRT Station.

Map of Bukit Nanas Forest Reserve, taken from one of the maps on display there. Click for larger view.

Continue from the Dang Wangi station by taking the overhead bridge across Jalan Ampang right in front of the station, and walking on in the direction of the KL Monorail Bukit Nanas Station. A short distance ahead, you will encounter a small gallery, Wariseni, and behind this gallery is a footpath into the Bukit Nanas Forest Reserve, taking you up the hill through a long flight of stairs. Climbing up can be a little tiring, so take your time.

The long flight of stairs up the hill takes you into the forest park.

The Jelutong Trail.

The first trail you can see branches off from this footpath, with its name clearly signposted – Jelutong Trail. This looping trail skirts the side of the reserve and the lower half of it is currently overgrown. However, the top half of the trail is still fine, and takes you past some large trees. Most of them are labeled with some information about them on wooden plaques mounted on pedestals. It soon becomes obvious why the trail is so named; jelutong (Dyera costulata) trees are obvious along the trail, and you will pass a huge jelutong tree if you continue along to the end (or start, if coming from the other direction) of the trail.

The big Jelutong (Dyera costulata) tree found by the side of the Jelutong Trail.

Surian Wangi (Toona sureni) tree with nice buttress roots. Many of the trees at Bukit Nanas are labeled, making it a great place for nature education.

Bamboo Walk, a pleasant stretch flanked by clumps of giant bamboo.

The Jelutong Trail allows you to cross onto the Bamboo Walk, a tiled pavement with huge bamboo clumps growing on the sides. Walking straight on the Bamboo Walk takes you through an old banana grove, where you can detour down to the Suboh Trail, a picturesque trail passing through the banana plantation. It takes you right to the edge of the forest reserve, bordering the Convent school, and ends at a small tarred road called Jalan Aquilaria that connects to Jalan Bukit Nanas.

Suboh Trail, a path set amongst banana trees, which changes to typical rainforest later on.

If you skip the Jelutong Trail and continue along the concrete stairway, you will pass a small built-up area to do calisthenics, with various apparatus as well. Continuing on will take you across a wooden bridge and onto a wide open “activities” area. It may be possible to camp here (with permission from the Forest Department). Right ahead, the KL Tower looms.

Wooden plank walkway at Bukit Nanas, which allows for observation of the surrounding rainforest understory.

Walking to the end of this open area leads you back into the forest. Here, you have a choice between taking the Merawan Trail, or the short plank walkway built over the forest floor. Both are interesting and short, so why not both? The former is another jungle trail that takes you past a few large trees like the Merawan Batu (Hopea beccariana), a dipterocarp, and a big Pulai tree (Alstonia angustiloba). The latter gives you a good picture of the understory structure of a typical Malayan rainforest, without having to get your feet dirty and passes one of the few patches in the forest reserve that still has an intact canopy.

The Merawan Trail is perhaps the quietest trail in the park. It is farthest from the outward city-facing edge of the forest, and traverses some nooks and crannies.

Merawan Batu (Hopea beccariana), found along the Merawan trail.

Large Pulai tree (Alstonia angustiloba), and the KL Tower, in view. Pulai is a common wayside/secondary forest tree in Malaysia, but they are usually not large. Here however, they are able to grow old and big.

If you take the Merawan Trail, it ends at a stairway and across it, the Penarahan Trail awaits, another short trail passing through a patch with more or less intact canopy (and rainforest structure). This trail is notable for having some unique, twisting lianas.

Penarahan Trail, a nice trail with some twisting lianas to be found.

The “undisturbed” rainforest of Bukit Nanas, as seen from the Penarahan Trail. Note the large liana.

Looking like a thick twisty rope, this climbing liana/vine coils around the tall trees to reach into the canopy and sunlight.

The Information Centre is located just off Jalan Raja Chulan and has a small exhibit with some old photos and information. Behind the Information Centre is a Herbal Garden exhibiting a variety of local herbs, an Orchid Garden,  and an Arboretum Trail nearby. At the time of this writing, construction of some sort of cable car or canopy “skywalk” was ongoing (and has been going on for the past 1.5 years at least).  If and when it is finally opened, it should be an added attraction in addition to the KL Tower, just a stone’s throw away. [Latest update – The Skywalk at Bukit Nanas is now open. It features a long walkway anchored by towers at up to about 20m above ground, and links the rear of the Information Center with the KL Tower entrance.]

The Bukit Nanas Skywalk

Inside the Bukit Nanas/KL Forest Eco-Park Information Center.

The Herbal Garden has some common and less common Malaysian herbs.

Wildlife

Someone relocated a troupe of silvered leaf monkeys (Trachypithecus cristatus) into the forest here; normally these monkeys are denizens of coastal/estuary forests, so I am not entirely sure if they can survive long term in this tiny forest. Here, they are totally unafraid of humans, so it may be they were relocated from the Kuala Selangor/Bukit Melawati area with its burgeoning population of silvered leaf monkeys.

KL Forest Eco-Park is home to perhaps 20 or so silvered leaf monkeys that were likely trans-located here. Notice the color of their young is very different from the adults.

Other than squirrels, skinks, snakes, small reptiles, some species of birds, and of course, numerous invertebrates, there doesn’t seem to be any other native wildlife remaining in this tiny green island surrounded by concrete jungle. There might be long tailed macaques (Macaca fascicularis), but I did not encounter any despite several trips here.

Large Batai (Paraserianthes falcataria) trees grow here at Bukit Nanas. These fast growing trees are not native to Malaysia, but those at Bukit Nanas are old due to being planted/established many years ago.

Summary

While I wouldn’t say the Bukit Nanas Forest Reserve/KL Forest Eco Park is a perfect example of what an undisturbed Malaysian tropical lowland rainforest ought to be, it is still a welcome respite from the stressful KL life, and a much needed green lung smack right in the middle of the city. It also presents an opportunity to study the changes that affect an isolated island of “primary” rainforest over a sustained period of time, especially with introduced species (some of the old trees appear to be planted or introduced here).

For a casual visit, it can be a pleasant place to enjoy nature, but due to its disturbed character/surroundings, mosquitoes can be quite common during wet weather, so mosquito repellant should come in handy here. Visiting hours are from 8 am to 5 pm daily.

Update August 10, 2016: Although it was always free to enter, today the KL Forestry Department announced that it would be charging an entrance fee (RM12 for adults/ RM4 for children).

For further information log on website :
https://www.rainforestjournal.com/a-walk-through-the-bukit-nanas-forest-reserve/

Development of Flexible Polyurethane Nanostructured Biocomposite Foams Derived from Palm Olein-Based Polyol

Advances in Materials Science and Engineering
Volume 2016 (2016), Article ID 4316424, 12 pages
http://dx.doi.org/10.1155/2016/4316424

Author

Srihanum Adnan, Tuan Noor Maznee Tuan Ismail, Norhayati Mohd Noor, Nik Siti Mariam Nek Mat Din, Nurul ‘Ain Hanzah, Yeong Shoot Kian, and Hazimah Abu Hassan

Synthesis Product Development Unit, Advanced Oleochemical Technology Division, Malaysian Palm Oil Board, No. 6, Persiaran Institusi, Bandar Baru Bangi, 43000 Kajang, Selangor, Malaysia

Received 27 August 2015; Revised 7 December 2015; Accepted 10 December 2015

Academic Editor: Michele Iafisco

Copyright © 2016 Srihanum Adnan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This study examined the effect of organoclay montmorillonite (OMMT) on the mechanical properties and morphology of flexible polyurethane/OMMT nanocomposite (PU/OMMT) foams prepared from petroleum- and palm olein-based polyols. Palm-based PU foams exhibited inferior mechanical strength as compared to neat petroleum PU foams. However, addition of OMMT significantly improved the foams strength of flexible polyurethane/OMMT nanocomposite foams prepared from palm olein-based polyol (PU bionanocomposite foam). The morphology analysed by scanning electron microscopy (SEM) showed that the cell size of the foam decreased with increasing OMMT content. PU bionanocomposite foam with 5 wt% of OMMT had the most improved tensile (63%) and tear (48%) strengths compared to its neat counterpart. Transmission electron microscopy (TEM) revealed the exfoliated structure of the respective foam. It was concluded that OMMT improved mechanical properties and morphology of PU foams.

1. Introduction

Polyurethanes (PUs) are recognized as the most versatile polymers. They consist of soft and hard segments. Factors that influence the properties and application suitability of the polyurethane include segmental flexibility, chain entanglement, interchain forces, and cross-linking [1]. Generally, polyurethanes are widely used in coatings, adhesives, foams, elastomers, and composites [2]. In making PUs, polyol is one of the main raw materials. Almost all polyurethanes are derived from petroleum-based raw materials. However, issues surrounding petrochemical derived feedstock including unpredictable petroleum price, sustainability, stability of production, environment impact, and waste disposal have led to studies on renewable raw materials. Over the years, polyols have been successfully developed from natural resources. Vegetable oils such as soybean, castor, palm, and canola oils have been reported to be the potential sources for natural polyols [3–7]. Polyols synthesised from cashew nut shell were also reported in the literature [8]. Nonetheless, the properties of vegetable oil derived PU are generally inferior in comparison to the petroleum derived counterparts due to the position of hydroxyl groups that are pendent in the aliphatic backbone of the triglycerides structure. In contrast, the petroleum-based polyols are telechelic polymers [9]. This contributes to lower physical properties of PU foam made from the former [9–12].

In general, to cope with the limitations such as low stiffness and low strength of polymers, particularly PUs derived from vegetable oils, inorganic fillers such as talc, glass, Al2O3, CaCO3, and SiO2 were used to enhance the mechanical properties of polymer composites [13]. Three main attributes of the fillers as reinforcement agents that impact the development of mechanical properties are chemistry, size, and shape [14]. The mechanism of the reinforcement is based on the higher resistance of rigid filler materials against straining due to their higher module. When a rigid filler is added to the soft polymer matrix, it will carry major portion of applied load to the polymer matrix under stress conditions, if the interfacial interactions between filler and matrix are adequate [15, 16].

It has been shown that dramatic improvements in mechanical properties can be achieved by incorporation of a few weight percentages (wt%) of inorganic clay minerals consisting of layered silicates in polymer matrices [17–21]. A commonly used layered silicate, montmorillonite (MMT), is dioctahedral clay of smectite group that have a thickness of ~1 nm and lateral dimensions of ~30 nm to several microns or larger. The large aspect ratios of layered silicates dominate the interaction with polymers, resulting in enhanced mechanical properties of particulate-polymer nanocomposites.

Nanocomposites can be defined as composites having more than one solid phase with a dimension in the range of 1–20 nm [1]. Intercalation of polymer chains between individual platelets of layered silicates introduced into the polymer is the key to the polymer nanocomposite technology. Therefore, it is crucial to completely disperse the silicate layers in the polymer matrix for the development of remarkable polymer nanocomposites. This is accomplished by the surface modification of montmorillonite (MMT) with organophilic groups. Since MMT is hydrophilic and lacks affinity with hydrophobic organic polymers, modification of MMT is needed in order to give partially hydrophobic character. OMMT is produced by exchange of metal cations in MMT with organic ammonium salts. The affinity of PU to the surface of the clay and the organic surfactant of the OMMT is essential to promote favourable interaction between these two materials [22].

There are three types of nanocomposites structures, which depend on the OMMT opening degree after integration with polymer matrix. The composites are classified as exfoliated or delaminated when silicate layers are fully dispersed in the matrix. This type of composite yields the greatest improvement in properties because maximum reinforcement is reached. Most of the composites reported in the literature are intercalated. Intercalated composites are categorised when the layers are partially open. Composites with closed layers (tactoid) are classified as immiscible [23].

Nanocomposites have been used commercially since the world largest car manufacturer, Toyota, introduced the first polymer/clay auto parts in the 1980s [24]. Since then, clay nanocomposites with several polymers such as polypropylene [25, 26], polyamide-6 [27], polystyrene [28], poly(methyl methacrylate) [29], poly(ethylene terephthalate) [30], elastomeric polyurethane [31], and polyurethane foam [32–34] were explored.

The effect of MMT on the palm oil-based rigid PUFs was studied by Chuayjuljit et al. [35]. Rigid PUFs were prepared with incorporation of 1, 3, and 5 wt% MMT in the formulation. Foam with incorporation of 5 wt% MMT showed the highest compressive strength of 172 kPa as compared to the neat foam of 117 kPa. In another study, integration of modified diaminopropane montmorillonite (DAP-MMT) into palm olein-based polyol improved the compressive strength of the rigid PU nanocomposite foams. It was reported that DAP-MMT was capable of reducing the cell size of the rigid PU nanocomposite foams without altering the chemical structure. Rigid PU nanocomposite foams exhibited exfoliated structure due to uniformly dispersed DAP-MMT within PU matrix. It was suggested that the formation of urea linkages between –NH2 groups of DAP-MMT and –NCO groups of diisocyanates could enhance the interfacial adhesion between filler and the matrix [36]. In a study carried out by Piszczyk et al. [37], modified MMT enhanced the compressive stress at 20% strain from 100 to 174 kPa of the rigid PUF. It was recommended that the presence of hydroxyl group of OMMT facilitates the dispersion of the nanofillers in the polyol mixture, hence resulting in improved compressive stress. In a similar way, comparative study of the properties of rigid PU/OMMT nanocomposite foams prepared using organoclay as blowing agent was conducted by Xu et al. [38]. The resultant foams demonstrated uniform and finer cell structures as compared to the rigid PUFs prepared from unmodified clay. Incorporation of up to 8 phr organoclay in the formulation revealed that rigid PUF with 2 phr organoclay resulted in the improvements of 110 and 152%, in the tensile and compressive strengths, respectively. The study also highlighted that the highest carbonyl hydrogen-bonding index (2.17) was achieved at 2 phr of organoclay. The index decreased (0.96) when incorporation of organoclay was more than 4 phr. The results from the study proved that finer cell structure of rigid PU/OMMT nanocomposite foams can be accomplished using organoclay as blowing agent. In addition, more hydrogen bonding between PU and organoclay contributes to the improvement of the strengths.

A great number of literatures addressed the improvement of mechanical and thermal performance of rigid polyurethane/organoclay nanocomposite foams [35–41]. These properties include heat and flame resistance, mechanical strength, gas barrier resistance, thermal stability, and ionic conductivity. However, studies on the effect of OMMT on palm oil-based flexible PUF are quite scarce.

The objectives of the study were to prepare flexible PU nanocomposite foams using palm olein-based polyol, Pioneer E-135 (US 7,932, 409) [42], and petroleum-based polyol with OMMT as nanoclay. The effects of the Pioneer E-135 as a drop in replacement for petroleum-based polyol in the formulation and the effects of OMMT on mechanical properties and morphology of flexible PU foams prepared from petroleum- and palm olein-based polyol and the respective PU/OMMT nanocomposite foams were investigated. The flexible PU foams produced could have a high potential to be used for mattresses or car seat.

2. Experimental

2.1. Materials

Nanoclay, Cloisite® 20A, a natural montmorillonite modified with a dimethyl, dihydrogenated tallow, quaternary ammonium with a concentration of 95 meq/100 g clay was purchased from Southern Clay Products (USA). Petroleum-based polyols, Poly-G® 85–29 (hydroxyl number 28 mg KOH/g, ethylene oxide capped polyether polyol, equivalent weight 2062) and Poly-G 92–27 (hydroxyl number 28 mg KOH/g, polyether polyol, equivalent weight 2004), were obtained from Arc Chemicals Inc. (China). Desmodur 3133 (polymeric diphenylmethane diisocyanate, pMDI) was purchased from Bayer (Malaysia). Pioneer E-135 was prepared by Malaysian Palm Oil Board (MPOB). In all formulations studied, water was used as the blowing agent. Catalysts, Dabco 33LV and Niax A-1, were purchased from Kimia Cergas (Malaysia) and dibutyltin dilaurate (DBTDL) was obtained from GoldShmidt (Malaysia). Surfactant, Tegostab B 4113, was purchased from Evonik (Malaysia). Lumulse POE 26 as a cell opener was obtained from Lambert Technologies (Malaysia). All materials were used as received.

2.2. Methods

The foam was prepared by mixing palm olein-based polyol (Pioneer E-135), commercial petroleum-based polyols, amine and tin catalyst, silicone surfactant, and water together in a plastic cup. The mixture was stirred under high shear rate with a mechanical stirrer at 2500 rpm for one minute. Then, an appropriate amount of pMDI which was calculated based on the isocyanate index was poured into the mixture. Stirring was continued and stopped just before the cream time. The mixture was then quickly poured into a plastic container (20 × 20 × 10 cm). The foam was allowed to rise and cured at 80°C in the oven for 10 minutes. The demoulded foams were hand crushed to open the cell windows. Mechanical and morphology analysis were conducted after aging the foams at 25°C for a minimum of 7 days.

Pioneer E-135 was synthesised from 100% RBD palm olein. Schematic diagram of the synthesis and flowchart of the production are given in Figures 1 and 2, respectively. The properties of Pioneer E-135 were provided by MPOB as shown in Table 1. In this study, four sets of PU foams were prepared. The first set of foams were prepared from 100% petroleum-based polyol and followed by PU foams made from 10%, 20%, and 30% palm olein-based polyol as a drop in replacement of the petroleum-based polyol. All foams prepared were incorporated with 3, 5 and 7 wt% OMMT. Formulations of PU foams prepared are shown in Table 2. Foams densities were in the range of 45 to 48 kg/m3. The designations of the PU foams are tabulated in Table 3.

Table 1: Properties of Pioneer E-135.

Table 2: Formulation of petroleum- and palm-based PU foams.

Table 3: Designations of the prepared PU foams.

Figure 1: Schematic diagram for the synthesis of polyol from palm olein.

Figure 2: Flowchart of the production of Pioneer E-135.

2.3. Fourier Transform Infrared (FTIR)

Identification of functional groups of neat petroleum- and palm-based PU foams and the nanocomposite foams was conducted using Perkin Elmer, Spectrum 100 FT-IR Spectrometer (Llantrisant, UK). The samples were scanned between 4000 and 650 cm−1 wavenumbers.

2.4. Tensile Properties

The test was conducted according to the ASTM D3574 (Test E). Foams were cut into flat sheets of 12.5 ± 1.5 mm thickness and stamped to dumb-bell shape as described in ASTM D 412. The test was carried out using Hounsfield S-Series Machine (Surrey, UK). The specimens were placed in the grips of the testing machine and pulled at a speed of 500 ± 50 mm/min. The tensile strength of the foam was obtained using the average value from three samples.

2.5. Tear Resistance

Tear resistance of the foams was determined using Hounsfield S-Series Machine (Surrey, UK) according to the ASTM D3574 (Test F). The specimens were clamped at the jaws of the testing machine and pulled across at the speed of 500 ± 50 mm/min.

2.6. Resilience

Foam resilience was measured according to ASTM D3574 (Test H). This test is principally a ball rebound test in which a steel ball is dropped from a prescribed height onto the sample and the percentage of recovered height is recorded. The specimen size was 100 mm × 100 mm × 50 mm. Average value of three specimens from different locations of a sample was recorded.

2.7. Scanning Electron Microscopy (SEM)

Morphology of the foam such as cell size was observed using Zeiss, Leo 1450 VP Scanning Electron Microscopy (Oberkochen, Germany). A thin piece of foam was carefully sliced with a sharp blade and stuck to aluminium stubs. The samples were then sputter-coated with a total of 15 nm of Au/Pd and observed under the microscope employing an accelerating voltage of 10 kV and a probe current of 6 × 10−11 amps.

2.8. Transmission Electron Microscopy (TEM)

Morphology of the PU/OMMT foam with 5 wt% OMMT was also studied using CM 12 Philips Transmission Electron Microscopy (Eindhoven, Netherlands). The 70 nm sectioned ribbons were placed on 400-mesh copper grids for imaging using TEM. The samples were imaged at high magnification of 28 000X with accelerating voltage of 100 kV.

3. Results and Discussion

3.1. Preparation of Polyurethane Bionanocomposite Foams

PU bionanocomposite foams were prepared by replacing petroleum-based polyol with 10 (PUF10), 20 (PUF20), and 30% (PUF30) Pioneer E-135 with incorporation of 3, 5, and 7 wt% OMMT in the formulation. Figures 3 and 4 show the PUF10 and PUF20 with incorporation of 3, 5, and 7 wt% OMMT, respectively. PUF10 exhibited uniform cell structures. In the case of PUF20 and PUF30, coarse cell structures were clearly evident. Therefore, the respective foams were not evaluated further due to the defects of the foams. Another defect, shrinkage phenomenon, was reported by Pawlik and Prociak [12] when more than 15% palm olein-based polyol was incorporated in the formulation. It was found that significant changes in the foam formulation are required in order to eliminate undesirable effects such as shrinkage, coarse cell structures, and collapse. The optimisation of the foam formulation, including quantities of catalysts and surfactant to be added, has to be studied.

Figure 3: PU bionanocomposite foams prepared from 10% Pioneer E-135 with incorporation of (a) 3 wt% OMMT, (b) 5 wt% OMMT, and (c) 7 wt% OMMT.

Figure 4: PU bionanocomposite foams prepared from 20% Pioneer E-135 with incorporation of (a) 3 wt% OMMT, (b) 5 wt% OMMT, and (c) 7 wt% OMMT.

3.2. Fourier Transform Infrared (FTIR)

In the synthesis of polyurethane (PU), there are a number of reactions that happen concurrently due to reactive isocyanate group, which reacts with molecules that have “active hydrogen” such as polyol (hydroxyl group), water, and amine [43], as illustrated in Figure 5. The most important reaction is between isocyanate and hydroxyl group of polyol (Reaction 1). This reaction leads to production of urethane group, which forms the majority of functional groups found in PU products. Water is used as a source of blowing agent in the production of PU foams, where it reacts with isocyanates to form unstable carbamic acid (Reaction 2). The unstable carbamic acid decomposes further to form amine compound and gaseous carbon dioxide. This reaction is a very convenient source of a gas, which is necessary to generate the cellular structure of polyurethane foams. The amine, which comes from diethanolamine (chain extender) or decomposed unstable carbamic acid, reacts with an isocyanate group and generates symmetrical disubstituted urea (Reaction 3). In this study, the reaction (Reaction 1) was catalysed by an organotin compound known as dibutyltin dilaurate (DBTDL). At high temperature, the reaction between isocyanate and urethane group leads to formation of an allophanate (Reaction 4) while the reaction between urea group and isocyanates leads to formation of biuret linkage (Reaction 5) [44]. Some of the reactions discussed above can be monitored via FTIR through their functionalities.

Figure 5: Schematic diagram for the reactions of isocyanates with (1) polyol, (2) water, (3) amine, (4) urethane, and (5) disubstituted urea in the synthesis of polyurethane. Source: Ionescu [44].

FTIR spectra of neat petroleum- and palm-based PU foams prepared with 3, 5, and 7 wt% OMMT are illustrated in Figures 6 and 7, respectively. The characteristic of FTIR spectra for PU nanocomposite and PU bionanocomposite foams was almost unchanged when compared to the neat petroleum- and palm-based PU foams. This could indicate that chemical structures of the neat petroleum- and palm-based PU foams were not affected by incorporation of OMMT [35, 45]. Broad stretching of hydrogen-bonded urethane, N–H, was observed at 3405 cm−1. The band at 2995–2860 cm−1 was attributed to the C–H stretching vibration. There was no stretching vibration band at 2270 cm−1 which is a characteristic peak of isocyanate (–N=C=O) group, indicating that all of the isocyanate groups reacted during polymerization. Wavenumbers at 1731–1718 cm−1and at 1685–1706 cm−1 are assignable to the stretching of hydrogen-bonded carbonyl groups which leads to ordered and disordered conformation, respectively. These hydrogen-bonded carbonyl groups can be observed at lower wavenumbers compared to non-H-bonded (free) carbonyls group which appears at 1731–1733 cm−1[45]. Combined motion of H–N–C=O in amide II was observed at 1510 cm−1 [46].

Figure 6: FTIR spectra of (a) neat petroleum PU foam and PU nanocomposite foams with (b) 3 wt% OMMT, (c) 5 wt% OMMT, and (d) 7 wt% OMMT.

Figure 7: FTIR spectra of (a) palm-based PU foam and PU bionanocomposite foams with (b) 3 wt% OMMT, (c) 5 wt% OMMT, and (d) 7 wt% OMMT.

3.3. Mechanical Properties

3.3.1. Tensile and Tear Resistance

Mechanical properties of nanoclay-based polymer composites can be directly affected by intercalation/exfoliation levels in nanocomposites morphology. Figures 8 and 9 illustrate tensile and tear strength of neat petroleum- and palm-based PU foams prepared with 3, 5, and 7 wt% OMMT, respectively. Addition of OMMT had an effect on the strength of the nanocomposite foams. The tensile and tear strengths of the nanocomposites improved with the addition of up to 5 wt% of OMMT. It shows a 33% (petroleum) and 63% (palm-based) increase of the tensile strength from 46.7 kPa and 42.0 kPa to 62.2 kPa and 68.4 kPa, respectively (Figure 8). The tear strength increased 13% (petroleum) and 48% (palm-based) from 147.5 N/m and 137.0 N/m to 167.3 N/m and 202.5 N/m, respectively (Figure 9). However, further incorporation of OMMT (7 wt%) reduced its strength due to the agglomeration of the OMMT within the PU matrix. According to Chan et al. [47] a large amount of nanoclay added in the system may agglomerate or cluster of nanoclay will be formed. It was observed that OMMT had a more significant effect on mechanical properties of PU bionanocomposite foams compared to PU nanocomposite foams. The strength of the PU bionanocomposite foams was higher than the PU nanocomposite foams, regardless of the amount of OMMT added, although the palm-based PU foams had a lower strength as compared to the neat petroleum PU foam. This phenomenon was supported with smaller cell size of PU bionanocomposite foams compared to the cell size of PU nanocomposite foams as shown by SEM images. It is well known that improved strength of the nanocomposite foams can be achieved by smaller and uniform cell sizes. According to Wilkinson et al. [48] strong H-bond formation between the edge hydroxyl groups of the silicate lamellae (mainly silanol, Si-OH, and aluminol, Al-OH) with urethane groups was able to improve the strength of the nanocomposite foams. A possible interaction mechanism of hydrogen bonding between the PU chain and OMMT is shown in Figure 10. In addition, the intercalant quaternary ammonium salts of the OMMT act as the “bridge” connecting the MMT layers and polymer chains [29]. Moreover the OMMT can interlock the polymer chains and eventually form strong barriers once it is subjected to a loading [47].

Figure 8: Tensile strength of PU nanocomposite foams and PU bionanocomposite foams with different amounts of OMMT.

Figure 9: Tear resistance of PU nanocomposite foams and PU bionanocomposite foams with different amounts of OMMT.

Figure 10: A possible interaction mechanism of hydrogen bonding between the PU chain and OMMT.

3.3.2. Resilience

Neat petroleum PU foam had better resilience than palm-based PU foam. Higher hard segment content in palm olein-based polyol decreases the resilience of PUF as reported by Rojek and Prociak [49]. Addition of OMMT had no apparent effect on the resilience of PU nanocomposite foams. However, resilience of the PU bionanocomposite foams increased 19–21% as compared to the palm-based PU foam as shown in Figure 11. The results indicated that the OMMT could help to improve resilience of the palm-based PU foam. This was due to the uniform dispersion of the OMMT within the PU matrix as the OMMT contains one long alkyl tail that leads to better dispersion of OMMT platelets in PU matrix [22]. PU bionanocomposite foams with addition of OMMT had resilience of more than 40%. ASTM D3574 (Test H) describes that flexible PU foams are referred to as having high resilience if resilience is greater than about 40%, thus reflected to PU bionanocomposite foams.

Figure 11: Resilience of PU nanocomposite foams and PU bionanocomposite foams with different amounts of OMMT.

3.4. Morphology Analysis

3.4.1. Scanning Electron Microscopy (SEM)

Information on cell shape and domain size can be determined by morphology of the foam. Figure 12 illustrates the cellular structure of the neat petroleum PU and the nanocomposite foams produced with 3, 5, and 7 wt% of OMMT, while the structures of the palm-based PU and the bionanocomposite foams produced with 3, 5, and 7 wt% of OMMT are shown in Figure 13. The micrographs revealed that neat petroleum PU foams and palm-based PU foam have fewer cells and a larger cell size than the respective nanocomposite foams. As the content of OMMT was increased, the average cell size decreased for neat nanocomposite foams incorporated with 3, 5, and 7 wt% OMMT. Cell size of neat petroleum PU foam has the average values of Ferrets diameter of 870 μm. It was reduced to 600, 523, and 450 μm with incorporation of 3, 5, and 7 wt% OMMT, respectively, whereas average values of Ferrets diameter for palm-based PU foam were 371 μm and those of PU bionanocomposite foams with incorporation of 3, 5, and 7 wt% OMMT were reduced to 290, 250, and 215 μm, respectively.

Figure 12: SEM micrographs of (a) neat petroleum PU foam and PU nanocomposite foams with (b) 3 wt% OMMT, (c) 5 wt% OMMT and (d) 7 wt% OMMT.

Figure 13: SEM micrographs of (a) palm-based PU foam and PU bionanocomposite foams with (b) 3 wt% OMMT (c) 5 wt% OMMT and (d) 7 wt% OMMT.

OMMT can act as a nucleation agent and affects nucleation efficiency due to its particle size [50, 51]. It serves as nucleation site for cell formation and since a higher number of cells start to nucleate at the same time, there is less gas available for their growth and this leads to a decrease in the size of the cell [52, 53]. From the micrograph, PU bionanocomposite foams exhibited uniformity in size and shape compared to PU nanocomposite foams due to secondary hydroxyl groups in palm oil [54].

3.4.2. Transmission Electron Microscopy (TEM)

Nanocomposite foams with incorporation of 5 wt% OMMT for both petroleum- and palm-based showed the highest improvement in tensile and tear strength; thus the exfoliation of the silicate layers was confirmed using TEM. A TEM image (Figure 14) of the PU nanocomposite foam with 5 wt% OMMT demonstrates intercalated structures. The dark lines represent the individual layers of OMMT which are aligned in the same direction whereas darker lines (circled area) show stacked silicate layers due to clustering or agglomeration. PU bionanocomposite foam prepared using 5 wt% OMMT shows a higher degree of exfoliated structures as shown in Figure 15. It can be seen that OMMT layers have reached nanometer scale where the average thickness appears to be just a few nanometers and the average length is about 100 nm. Exfoliated structures of PU bionanocomposite foam with 5 wt% OMMT correlate well with significant improvement of its mechanical properties.

Figure 14: TEM image of PU nanocomposite foams with 5 wt% OMMT.

Figure 15: TEM image of PU bionanocomposite foams with 5 wt% OMMT.

4. Conclusion

Incorporation of 5 wt% OMMT improved the mechanical properties and morphology of PU nano- and bionanocomposite foams as compared to their neat PU foams. PU bionanocomposite foams showed the most significant improvement. TEM images revealed homogenous dispersion of OMMT in polymer matrix as it exhibited exfoliated structure. Smaller cell sizes were observed for PU bionanocomposites foam with incorporation of 5 wt% OMMT and this in return improved 63%, 48%, and 21% of tensile and tear strength and resilience, respectively. Incorporation of more than 5 wt% OMMT however reduced the average performance of the PU nanocomposite foams.

Conflict of Interests

The authors have declared no conflict of interests.

Acknowledgments

The research team wishes to sincerely acknowledge the Director General of MPOB for her permission to carry out this work. A special appreciation is devoted to Polymer and Composites Group for the analyses of the samples. Contribution by Ramli MR in preparation of the paper is greatly appreciated.

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