Characteristics of Linerboard and Corrugated Medium Paper Made from Durian Rinds Chemi-mechanical Pulp

In recent years, there has been tremendous growth of interest in the utilization of non-wood based material to support the insufficient raw materials availability for the pulp and paper industry. Therefore, this study was conducted to investigate the characteristics of 120 gsm linerboard and corrugated medium paper made from unbeaten durian rinds chemimechanical (CMP) pulp. The linerboard and corrugated medium paper were prepared and tested according to Malaysian Standards / International Organization for Standardization (MS ISO) and Technical Association of the Pulp and Paper Industry (TAPPI) standard methods. Based on the burst index (2.03 kPa.m/g), RCT (1.97 N.m/g) and CMT (129N), the linerboard and corrugated medium from CMP durian rind pulp have shown a good potential as an alternative raw material for papermaking and comparable with other types of wood and nonwood based papers as well as current commercial papers.


Introduction
Nowadays, insufficient supply of wood-based raw materials for packaging industries due to environmental issues leads to tremendous interest in the utilization of non-wood based materials in papermaking.In Malaysia, almost 50% of total paper consumption comes from packaging papers [1,2].The country is a net importer of pulp and paper in order to satisfy the domestic consumption [3].Eighteen (18) out of 20 Malaysian paper mills utilize 95% waste paper and old corrugated carton (OCC) as their main raw material, with the exception of Kimberly-Clark (M) Bhd. and Sabah Forest Industries that use 80% imported virgin pulp and 100% mixed tropical hardwood pulp, respectively [4].In short, the paper and paperboard industries in Malaysia utilize imported virgin long-fiber pulp and secondary fibers, such as the old corrugated container (OCC) and waste papers to produce packaging papers [5].In order to reduce the dependence on imported pulps, various researches have been conducted on the utilization of agricultural wastes as raw material alternatives for packaging paper such as kenaf [1,2,6], coir [5], oil palm empty fruit bunch [7,8], Semantan bamboo [9] and oil a Corresponding author : srizal@uthm.edu.mypalm male flower spikes [10,11].Malaysia has an abundance of agro waste materials which have not been fully utilized [12].Malaysia is one of the major fresh and frozen durian exporters besides Thailand and Indonesia [13][14][15].In Malaysia, based on a study by Amid and Mirhosseini [16] stated that the rind constitutes in average about 45% for each mature fruit, Aditiya et al. [15] have calculated that durian rind waste generates about 133,688 to 171,303.9 metric tons from the year of 2006 until 2013 [15].According to Ministry of Agriculture and Agro-based Industry Malaysia (MOA) [17], there were 376,565 metric tons of durian fruits were produced in 2014.Thus, massive amounts of the durian peels waste are disposed of, causing a severe problem in the community [18].Therefore, the utilization of the durian rinds waste as pulp and paper alternative raw material would be beneficial.However, based on the authors' best knowledge there were limited research attentions and published works on the utilization of durian rinds waste as an alternative papermaking material.
The author previous study by Masrol, Ibrahim and Adnan [19] has successfully produced durian rinds pulp via chemi-mechanical pulping (CMP).In order to extend the study on utilizing durian rinds waste as packaging alternative raw material, this study was conducted to investigate the potential of durian rinds CMP pulp as linerboard and corrugated medium paper.

Raw material preparations
Durian rinds were collected from a local durian flesh manufacturer at Batu Pahat, Johor, Malaysia.Only the rinds of D24 durian have been collected to ensure the accuracy and repeatability of results.Firstly, durian rinds were cleaned from the residual aril and dirt.Then, the cleaned durian rinds were sliced, spine removed, cubed and dried naturally according to a procedure developed by Masrol et al. [19].Finally, the dried durian rinds were stored inside air-tight storage to prevent moisture and fungus infestation.

Chemi-mechanical pulping process
Durian rinds pulp was produced by a chemi-mechanical pulping process according to pulping conditions conducted by Masrol et al. [19].Dried durian rinds were treated with 10% (based on raw material oven-dry (o.d.) weight) solution of Sodium Hydroxide (NaOH) at room temperature for 2 hours.Then, the treated durian rinds were refined by Sprout-Waldron refiner mechanical pulping (RMP) machine to produce pulp.Refiner mechanical pulping (RMP) is preferred because of its low production, labor and capital costs [20].After the RMP process, screening was carried out using PTI Sommerville Fractionators according to TAPPI T 275 standard with a slot size of 0.15 mm.After the screening, a spin-dry Neng Shin extractor was used to remove excess water and the screened pulp was dispersed into smaller size using a Hobart mixer.Finally, durian rinds CMP pulps were sealed in polyethylene bags and stored inside chillers at a temperature of 6°C before laboratory hand sheets preparation.

Laboratory hand sheet preparation
Laboratory hand sheets with a grammage of 120±3 g/m 2 were produced from unbleached and unbeaten durian rinds chemi-mechanical pulp using a semi-automatic sheet machine (British Handsheet Machine) based on MS ISO 5269 Atmosphere for Conditioning and Testing and Procedure for Monitoring the Atmosphere and Conditioning of samples (ISO 187: 1990, IDT)" for at least 24 hours before further evaluation.

Characteristics' tests
The characteristics' tests (a-h) listed in Table 1

Ring crush test (RCT) and corrugated medium test (CMT)
The ring crush test (RCT) can be defined as an edgewise compression strength test of corrugated boards which is intended to characterize a paperboard's resistance to crushing by in-plane compressive forces.RCT is used for test liner and other papers used in packaging manufacture [21].
The test specimen with a dimension of 12.7 mm width x 152.44 mm length is cut by a strip punch as shown in Figure 1a and inserted into the sample holder (Figure 1b).Samples were tested using the L & W Crush Tester to measure the compression force required before the test specimens buckle as shown in Figure 1c.

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CMT can be defined as a test to measure the flat compression strength of a laboratory fluted strip of a corrugating medium and can be used as a basis for judgment of fabrication efficiency.The CMT permits the evaluation of corrugating medium before it is fabricated into combined board [22].The test specimen with the size of 12.7mm wide x 152.4 mm long is cut by a special die cutter and formed into a flute shape using Concora Medium Fluter in Figure 2a.The rack and comb inside the fluter machine work to perfectly shape the sample into flute shape as shown in Figure 2b.Samples were tested using the same L & W Crush Tester machine shown in Figure 1c.

Water absorption test (Cobb 30 test)
The purpose of this method is to determine the quantity of water absorbed by a linerboard in a specified time.Distilled water is used for the test to avoid any substance factor that can affect the absorption characteristics of the paper tested.The weight of the sample is measured before and after the test (Figure 3a and Figure 3d).The samples were tested for water penetration for at 20±1 seconds within 30±1 seconds total test time as shown in Figure 3c.

Laboratory hand sheet characteristics
Table 2 shows the physical and optical characteristics of 120 gsm linerboard produced from durian rinds chemi-mechanical pulp (CMP).The number of folds for 120 gsm linerboard (37) was higher compared to 15 by previous 60 gsm paper [19].For optical characteristics, ISO brightness (13.20%) and opacity (97.73%) are similar with Masrol et al. [19].The result of Cobb 30 test (225 g/m 2 ) shows that water penetrates durian rinds CMP linerboard too fast.This result could be improved by the addition of a sizing agent such as starch during the paper sheet preparation in the future.

Comparison of burst index, RCT and CMT with other types of paper
Table 4 shows that RCT results of durian rinds 120 gsm linerboard and corrugated medium made from CMP pulp are comparable with other paper types and commercial linerboards.
Linerboards with a high apparent density indicates a good bonding ability between fibers during paper formation [5].In this study, the durian rinds linerboard produced has an apparent density of 0.73 g/cm 3 which is similar with other non-wood based and commercial linerboards (Table 4).Apparent density is one of the most significant properties of paper and influences almost all mechanical, physical, and electrical properties [8].
In industrial practices, burst strength indirectly measures the internal resistance of corrugated box container to any kind of force applied [5].The burst index of durian rinds CMP linerboard recorded a value of 2.03 kPa.m 2 /g which is higher than some commercial linerboards' minimum requirement such as GSPP IL3, GSPP IL4, GSPP IL5, GSPP IL6, Pascorp IL1, Pascorp IL4, Pascorp IL4 and Pascorp IL6 reported by Main et al. [5].The burst index for durian rinds linerboard is also higher than commercial scale linerboards developed by Rushdan [8] except for SANYEN 6 and SANYEN 13.Unbeaten durian rinds CMP linerboard recorded RCT value of 1.58 kN/m and 1.97 N.m 2 /g for RCT index.For RCT index, durian rinds CMP linerboard recorded a higher value than the minimum requirement of commercial linerboards by GSPP and Pascorp as reported by Main et al. [5].RCT of

Table 1 .
were conducted according to ISO 5270: 2012 "Pulps -Laboratory sheets determination of physical properties" with accordance to Malaysian Standards / International Organization for Standardization (MS ISO).The test for CMT, RCT and Cobb 30 used for packaging grade paper (Table 1) were carried out in this study.All tests were performed in a controlled temperature and humidity environment as stipulated in TAPPI T 402 sp-03 "Standard Conditioning and Testing Atmospheres for Paper, Board, Pulp Handsheets and Related Products" and MS ISO 187: 2001 "Paper, Board and Pulps -Standard Atmosphere for Conditioning and Testing and Procedure for Monitoring the Atmosphere and Conditioning of samples (ISO 187: 1990, IDT)".The sampling was conducted according to TAPPI T400 sp-02 "Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product" and MS ISO 186: 2002, IDT "Paper and Board -Sampling to Determine Average Quality".Characteristics' tests list and standards

Table 2 .
Physical and optical characteristics of durian rinds linerboard

Table 3 .
Mechanical properties of durian rinds CMP compared with another types of linerboard