polyme s
A icle
Mo phological Analysis o Se e al Bamboo Species wi h
Po en ial S uc u al Applica ions
Asie Elejos e 1,*, Al onso A e alillo 2, Nago e Gabilondo 1, Amaia Bu on 2,* and C is ina Peña-Rod iguez 1,*
Ci a ion: Elejos e, A.; A e alillo, A.;
Gabilondo, N.; Bu on, A.;
Peña-Rod iguez, C. Mo phological
Analysis o Se e al Bamboo Species
wi h Po en ial S uc u al Applica ions.
Polyme s 2021,13, 2126.
h ps://doi.o g/10.3390/polym13132126
Academic Edi o s: Raul Fanguei o,
Jö g Müssig and Diana Fe ei a
Recei ed: 29 May 2021
Accep ed: 23 June 2021
Published: 28 June 2021
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
1
‘Ma e ials + Tecnologies’ Resea ch G oup, Chemis y and En i onmen al Enginee ing Depa men , Facul y o
Enginee ing, Gipuzkoa, Uni e si y o he Basque Coun y (UPV/EHU), Plaza Eu opa 1,
20018 Donos ia, Spain; [email p o ec ed]
2TECNALIA, Basque Resea ch and Technology Alliance (BRTA), Sede Azpei ia, Á ea Ana di 5,
E-20730 Azpei ia-Gipuzkoa, Spain; [email p o ec ed]
*Co espondence: asie [email p o ec ed] (A.E.); [email p o ec ed] (A.B.);
[email p o ec ed] (C.P.-R.)
Abs ac :
Bamboo cons i u es a amily o plan s ha a e e y p omising and in e es ing as enewable
ma e ials o bo h la ge and small s uc u e cons uc ion. To be used as an al e na i e o adi ional
ma e ials; he unde s anding o i s mo phology and mechanical beha io is o c ucial impo ance.
As he dis ibu ion o ibe s and ascula bundles di e s o each ype o bamboo; se e al bamboo
ypes ha e been cha ac e ized: Phyllos achys au ea (PA), A undina ia amabilis (AA) and Dend o-
calamus s ic us (DS). Mo phological analysis has been pe o med by op ical (OM) and scanning
elec on mic oscopy (SEM). Di e ences in densi y; su ace mo phology and wall hickness ha e
been ound. In ac ; PA and AA ha e shown a g ea mo phological egula i y; while DS p esen s he
g ea es hickness; o he poin ha i can be conside ed ull culm. The plan ’s own duc s cons i u e a
e y impo an ac o o u u e imp egna ions and he op imiza ion o mechanical p ope ies o
s uc u e cons uc ion.
Keywo ds:
bamboo; Phyllos achys au ea; A undina ia amabilis; Dend ocalamus s ic us; mo phology
1. In oduc ion
Due o inc easing en i onmen al conce ns, he scien i ic communi y in he ield o
ma e ials science is s i ing o ind new enewable s uc u al ma e ials. In his con ex ,
bamboo is gaining g ea e ecogni ion in he ma ke place amongs consume s o sus ainable
and en i onmen ally iendly ma e ials [
1
–
5
], ep esen ing a g eene al e na i e han he
no mally employed less sus ainable ma e ials. Indeed, in compa ison o wood, which is
cha ac e ized by a long g ow h cycle [
6
,
7
], he comp essi e s eng h o bamboo is wo
imes highe compa ed o conc e e and i s ensile s eng h is almos equal o ha o s eel.
Di e en es s ha e shown ha he ul ima e ensile s eng h o bamboo anges om 140 o
280 N/mm
2
, equal o mild s eel [
8
]. By using bamboo as a cons uc ion ma e ial, economic
and ecological bene i s a e ob ained, as can be seen in he s udy by Nayak e al. [
9
],
which compa ed he cos o s eel ein o cemen wi h bamboo ein o cemen . This s udy
showed ha some bamboo species ha e a ensile s eng h equi alen o ha o mild s eel
and wo k e y well in bending. I is also an added bene i in ea hquake-p one a eas due
o he ene gy abso p ion capaci y o bamboo. This s udy concludes ha he use o bamboo
as a subs i u e o s eel ein o cemen is a good op ion in low-cos s uc u es, being h ee
imes cheape .
Bagchi e al. [
10
] conduc ed se e al simila s udies on he use o bamboo as a con-
s uc ion ma e ial o eplace s anda d conc e e ma e ial. They also came o he conclusion
ha he ela ionship be ween bamboo’s mechanical p ope ies and cos makes i a e y
good al e na i e o conc e e as an en i onmen ally iendly building ma e ial, due o i s
high s eng h and low cos [
11
]. Bamboo egene a es as e and p oduces less was age o
Polyme s 2021,13, 2126. h ps://doi.o g/10.3390/polym13132126 h ps://www.mdpi.com/jou nal/polyme s
Polyme s 2021,13, 2126 2 o 13
aw ma e ial in p uning. In addi ion, se e al au ho s indica e ha bamboo e ains la ge
amoun s o ca bon han ees, which is c ucial o he educ ion o he g eenhouse e ec
and he igh agains clima e change [
12
–
14
]. Bamboo is included in he Bambusoideae sub-
amily, wi h a ound 90 gene a and mo e han 1200 species. Bamboo g ows na u ally in all
he con inen s, being especially abundan in Asia, wi h 65% o he o al wo ld p oduc ion,
mainly in China, ollowed by Cen al and Sou h Ame ica wi h 28% and A ica wi h 7%.
Howe e , B azil possesses he wides a ie y o bamboo species [
15
–
17
]. Bamboo co e s a
g ow h a ea o almos 38,000 million hec a es, app oxima ely 3.2% o he o al o es a ea
a ound he wo ld. Rega ding he cul i a ion o bamboo, i is es ima ed ha he e a e 22
million hec a es a ound he wo ld wi h nea ly 4000 di e en uses [
18
]. The cul i a ion
o bamboo is desi able as i p o ec s agains soil e osion, can be g own in acidic land
and i is o en used o eco e deg aded a eas as i sp eads o inhospi able egions whe e
o he plan s will ne e su i e. Howe e , bamboo is s ill no well known ac oss Wes e n
ci iliza ion [12].
As a s uc u al ma e ial, bamboo p o ides bo h high speci ic s eng h and igidi y,
and low wa e abso p ion compa ed o wood [
19
,
20
]. The speci ic s eng h o bamboo is
also highe han ha o o he common s uc u al ma e ials such as wood-based composi es,
conc e e, and s eel [
21
,
22
]. Howe e , as wi h o he species, bamboo usually p esen s a
hollow culm and, subsequen ly, mechanical p ope ies a y along he plan , limi ing i s use
in cons uc ion as a s uc u al ma e ial [
23
]. Due o i s mo phological cha ac e is ics, i is
mainly used in he o m o bamboo de i a i es, o u ni u e p oduc ion, loo ing and in
cons uc ion and ci il enginee ing [
24
]. Indeed, bamboo has been used as a homogeneous
cons uc ion ma e ial only in he o m o lamina ed boa ds o complex composi e ma e ials,
once he ini ial bamboo culms a e des oyed and ep ocessed; i.e., he ibe s a e sepa a ed
and la e pu back oge he a i icially [
19
,
25
–
32
]. Howe e , he en i e bamboo culm
could be sa is ac o ily used o cons uc ion pu poses, such as ailings, balconies, o small
s uc u es o suppo elec ical wi ing, aking ad an age o he na i e e ec i e o ien a ion
o cellulose ibe s. In o de o use bamboo in i s o iginal o m as a s uc u al ma e ial,
he i s s ep mus be o unde s and i s mo phology, hus enabling i s ea men in a mo e
e icien way.
The schema ic s uc u e o bamboo plan s is shown in Figu e 1. Bamboo is composed
o culms wi h solid ans e se diaph agms o nodes sepa a ing di e en hollow in e -nodal
egions (Figu e 1a). Unidi ec ional cellulosic ibe s a e o ien ed pa allel o he longi udinal
axis o he culm (Figu e 1b) and embedded in he pa enchyma issue ma ix composing he
ci cula c oss sec ion (Figu e 1c) [
12
]. This pa enchyma issue ma ix ligni ies and ha dens
as he culm ma u es, leading o inc eased densi y and imp o ed mechanical p ope ies.
Only a ew s udies ha e been ca ied ou on he mo phology o bamboo, mos o hem
ocused on Guadua o o he species no analyzed in his wo k [
1
,
23
]. Howe e , e en i he
epo ed s udies a e mos ly ela ed o o he p ope ies o p ac ices o bamboo, hey usually
e e o i s mo phology [
20
,
24
,
27
,
33
,
34
] e ealing he necessi y o a deepe compa a i e
s udy in o de o be e unde s and he in e nal s uc u e o he plan and he way o use i .
The knowledge ela ed o he mo phology o he plan is equi ed in o de o sol e
he wo main limi a ions o bamboo: he du abili y o he s uc u e and he he e ogenei y
o he plan in e ms o mechanical p ope ies. One o he p oposed s a egies is he
imp egna ion o he culm o bamboo wi h sui able esins. Fo ha , in his wo k, he ibe
and duc dis ibu ion has been analyzed o h ee bamboo species o iden i y he mos
sui able imp egna ion condi ions in o de o gene a e ma e ials wi h e icien ansmission
o s esses om he ma ix o he ibe s.
Polyme s 2021,13, 2126 3 o 13
Figu e 1.
Bamboo scheme: (
a
) iew o he plan om he g ound o he beginning o he b anches,
(b) longi udinal and ans e se sec ioned iew and (c) ci cula c oss sec ion.
2. Ma e ials and Me hods
2.1. Ma e ials
The mos common bamboos used o he manu ac u e o small s uc u es ha e been
selec ed o his wo k. Culms o PA bamboo (Phyllos achys au ea), AA bamboo (A undina ia
amabilis), and DS bamboo (Dend ocalamus s ic us) we e gen ly p o ided by Bambusa.
They we e imp egna ed by imme sion in bo ax sal s o p ese a ion. The employed
ma e ials we e young bamboo culms g own a e a leas six cu ing/g owing cycles o
he plan . The culms ob ained in he se en h g ow o he bamboo plan can be conside ed
homogeneous in e ms o mo phological and mechanical p ope ies. PA comes om Anji
Coun y, Huzhou, Zhejiang, a an al i ude o 200 o 500 m, wi h an ambien empe a u e o
18
◦
C wi h highs o 28 and lows o
−
3, humidi y o 5.47
±
0.61%, p esen ing a densi y o
863 kg/m
3
(362 kg/m
3
i he hollow cen e is aken in o accoun ). AA comes om Anji
Coun y, Huzhou, Zhejiang, a an al i ude o 200 o 500 m, wi h an ambien empe a u e
a ound o 18
◦
C wi h highs o 28 and lows o
−
3, humidi y o 5.72
±
0.15%, p esen ing
a densi y o 940 kg/m
3
(497 kg/m
3
i he hollow cen e is aken in o accoun ). DS comes
om Kanchanabu i, Thailand a an al i ude o 400 o 600 m wi h an ambien empe a u e
be ween 10 and 30
◦
C and a humidi y o 6.6
±
0.7%, p esen ing a densi y o 624 kg/m
3
.
Fo all he s udy and subsequen es s, he en i e culm has been used, as he inal objec i e
is he use o he comple e culm in s uc u es.
2.2. Me hods
A Nikon OM E80i mic oscope was used o op ical mic oscopy (OM) (Nikon Co po-
a ion, Japan) cha ac e iza ion bo h in ansmission and e lec ion modes. The samples
we e i s ly imme sed in dis illed wa e , unde acuum o wa e pene a ion, and hen
main ained in boiling wa e o 1 min. The so ened samples we e cooled down and cu
using a Leica Ul acu R mic o ome equipped wi h a diamond kni e in ec angula pieces
o 0.2 mm in hickness o ansmission and 10 mm o e lec ion.
Scanning elec on mic oscopy (SEM) (Hi achi, L d., Chiyoda, Tokyo, Japan) cha ac-
e iza ion was pe o med wi h a Hi achi S-4800 mic oscope a di e en magni ica ions.
SEM mic og aphs o 15 nm gold-coa ed samples we e ob ained a 10 kV.
3. Resul s and Discussion
3.1. Gene al Mo phology o Bamboo
The culm is he pa be ween he oo s and b anches, which makes up app oxima ely
wo hi ds o he plan (Figu e 1a). The gene al mo phology o he bamboo culm was
Polyme s 2021,13, 2126 4 o 13
analyzed by OM in bo h e lec ion and ansmission modes. Images ob ained om he
c oss-sec ion ( ans e sal cu ) o AA bamboo culm a e shown in Figu e 2.
Figu e 2.
OM mic og aphs om he c oss-sec ion o AA bamboo as ob ained by (
a
) e lec ion and (
b
)
ansmission modes.
As could be obse ed, he ibe s we e mo e isible in he images ob ained in e lec ion
mode (Figu e 2a). The ibe packages appea da ke due o he loss o ligh a he bo om o
he ibe s, whe eas he pa enchyma appea ed b igh due o i s highe e lec ion capaci y.
This image is i ually he nega i e o he image ob ained in ansmission (Figu e 2b).
The di e en elemen s o he culm can be iden i ied wi h mo e de ail om he OM
images shown in Figu e 3.
Figu e 3.
OM mic og aphs om he c oss-sec ion o AA bamboo: (
a
) ans e sal cu and (
b
) ascula
bundle in de ail.
As can be obse ed, ascula bundles make up he epea ing pa e n all along he
c oss-sec ion o he culm (Figu e 3b). Those ibe packages o shea hs a e esponsible o
main aining he shape and s uc u al in eg i y o he plan . The la ges ibe shea h is
composed o xylem o p o oxylem, whe eas he smalles one, always close o he ou e
pa o he bamboo culm, con ains phloem ibe s. Vascula bundles a e he b igh es
g oupings seen in he image due o he ligh ansmission h ough he ibe s. On he o he
hand, he da kes a eas obse ed in he image, hose be ween he ibe packages, a e small
pa enchyma cells (Figu e 3b). Pa enchyma, as one o he so-called undamen al issues,
is in ol ed in a wide a ie y o unc ions such as pho osyn hesis, s o age, p ocessing o
o ganic subs ances and issue egene a ion. Pa enchyma appea ed da ke in his case
due o he highe densi y o he issue o small-sized cells. In addi ion, o he ascula
elemen s ha allow ligh ansmission appea in Figu e 3. These e e o he me axylem
essels, which a e he pipes esponsible o wa e and ood anspo h oughou he plan .
These duc s a e clea ly obse ed in Figu e 3a. As is well known, lignin is he a oma ic
biopolyme esponsible o ein o cing he s uc u e o majo plan s, keeping all plan cells
s uck oge he , which is also he case o bamboo. Mo eo e , he ole o lignin in me axylem
Polyme s 2021,13, 2126 5 o 13
essels is especially impo an because as i is no wa e -soluble; i p e en s he me axylem
essels om collapsing due o he wa e low. Lignin also con ibu es o he mal s abili y
by p o iding s uc u al igidi y, he lignin con en anges om 18.35% o 25.80% [35–37].
In summa y, h ee elemen s can be di e en ia ed in he inne pa o he culm:
ibe s, duc s o me axylem essels, and pa enchyma (Figu e 3b). The ibe s a e he s uc-
u al pa o he plan , p o iding he equi ed s eng h o s and up igh and cope wi h
he ex e nal mechanical s ess. The duc s ensu e he ci cula ion o wa e and nu ien s,
while he pa enchyma cells pa icipa e in ood s o age. Finally, lignin keeps his ne wo k
o cells, condui s, and ibe s s uck oge he . The dis ibu ion o hese elemen s in e ms o
pe cen ages and densi ies depends no only on he species analyzed, bu also on he pa o
he culm sec ion ha is being analyzed.
F om he OM images o he ansi ion zone in AA bamboo shown in Figu e 4, he ap-
pea ance o di e en ea u es can be obse ed. Fibe shea hs a e almos geome ically
pe ec in shape (Figu e 4a), while i pa enchyma is analyzed (Figu e 4b), cells show
di e en shapes and sizes, g ouped in a much mo e e a ic way.
Figu e 4.
Op ical mic og aphs om he ansi ion zone o AA bamboo: (
a
) ans e sal cu o ibe
shea hs and (b) ans e sal cu o pa enchyma.
As can be app ecia ed om SEM images o PA bamboo shown in Figu e 5, he as-
cula bundles cons i u e he pa e n ha is epea ed h oughou he ans e sal sec ion o
he bamboo culm. Taking in o accoun ha he g ow h o he plan occu s only apically,
he o m and dis ibu ion o he ibe s, me axylem essels and duc s o he culm is main-
ained om he base o he end. Howe e , his pa e n is sligh ly a ec ed nea he nodes,
whe e mo e adial con ac appea s be ween he ibe s and he duc s, hus gi ing he plan a
g ea e esis ance o o sional s esses [
38
]. In he in e nodes, bo h he duc s and he ibe s
a e axially o ien ed, while he nodes p o ide he ans e se in e connec ion. As can be
seen in OM mic og aphs shown in Figu e 6, in some nodes, small packages o ibe s can be
ound e en in he ans e se di ec ion (indica ed wi h a ows). This dis ibu ion, in ad-
di ion o imp o ing he esis ance o o sion o combined o ces [
39
–
42
], also allows he
plan o e ain i s in eg i y and makes he culm ac u e much mo e di icul [
39
,
40
,
43
,
44
].
Thus, he node is he mos esis an pa o he bamboo, as can be ead in he s udy by
Chen [
45
], which, among he da a p o ided, we can ind a ensile s eng h o 130.93 MPa
o in e nodes and 162.12 MPa o nodes.
In o de o analyze he mo phological ea u es close o he limi s o he ci cula sec ion
a bamboo culm, longi udinal cu s we e also pe o med, as shown in Figu e 7. These a eas
a e di icul o obse e in he ans e se cu s as hey a e usually damaged du ing sample
p epa a ion. When cu ing he specimens, he so e inne pa is de o med by c ushing,
while he mos b i le ou e one ends o splin e . In Figu e 7a he ou e pa is clea ly
isible, composed by he co ex and he epide mis and he wax ha p o ec s he culm [
38
].
In he inne pa (Figu e 7b), he highes concen a ion o pa enchyma cells is obse ed
along wi h scle enchyma cells, which a e usually dead cells wi h hickened and ligni ied
seconda y walls [
23
]. The scle enchyma, one o he h ee ypes o undamen al issues in
Polyme s 2021,13, 2126 6 o 13
plan s, is composed o igid and non-s e chable cells and is gene ally ound in disused
pa s o plan bodies, such as ma u e s ems [
23
,
46
,
47
]. As can be seen, he s aigh ness
o he lines ha appea diminishes close o he inne pa , agg a a ed especially by he
diso de ed accumula ion o cells.
Figu e 5. SEM images o ans e sal cu o PA bamboo wi h di e en magni ica ions.
Figu e 6. Op ical mic og aph om he ans e sal cu in a node o AA bamboo.
Figu e 7. OM mic og aphs om longi udinal cu s o AA bamboo: (a) ou e pa and (b) inne pa .
In he inne mos pa o he culm, he size o ibe packages g adually dec eases o
disappea , as can be seen in Figu e 7b. The pa enchyma cells ake on mo e ele ance,
Polyme s 2021,13, 2126 7 o 13
wi h la ge a eas composed exclusi ely o pa enchyma obse ed. The amoun o me axylem
essel is also inc eased in his a ea. This speci ic way o g ouping oge he he di e en cells,
wi h he g ea e impo ance o ibe s ou side and ood s o age inside, u ns he bamboo
culm in o a ba wi h an ex ao dina y geome y. Fo any ba , ega dless o he ma e ial,
mechanical s esses ( ensile, comp ession, o sion, e c.) will concen a e a he ou e mos
pa . The e o e, he e olu ion o species has made mos o he ibe s concen a ed a he
a ea in which hey a e mos needed. This concen a ion dec eases when app oaching he
inne pa , and inally comple ely disappea s. In Figu e 5, he comple e sec ion o he
bamboo wall can be seen. In ha image, he duc s dis ibu ion can be easily iden i ied.
I can be obse ed ha in he ou e pa o culm, duc s become smalle un il hey disappea ,
due o he ac ha he ascula bundles a e massi e and comp essed. In he inne pa
o he culm, hey become la ge un il hey disappea , and wi h hem, also he ibe s.
In his way, wi h espec o he s uc u al elemen s o he bamboo culm, he longi udinal
ibe s o he culm and he lignin keep hem compac and p o ide ensile, comp ession
and lexu al s eng h. Ins ead, he ans e sal ibe s loca ed in he nodes and he lignin
p e en ela i e longi udinal displacemen be ween ibe s, p o iding o sion s eng h.
In Figu e 8, he elemen s o ascula bundle and pa enchyma a e shown by SEM images
wi h highe magni ica ion.
Along he whole leng h o he me axylem essel small holes a e app ecia ed, o sup-
plying nu ien s o cells (Figu e 8a). In he zone o pa enchyma cells (Figu e 8b), he a o e-
men ioned small duc s a e also obse ed, allowing nu ien ansmission. The ans e sal
connec ion be ween essels and pa enchyma cells is shown in de ail in Figu e 8c. The liquid
low in he ans e sal di ec ion is possible due o he in e connec ion o cells by hese
small pi s (Figu e 8b). This is because he ho izon al mo emen o conduc i e essels
owa ds he neighbo ing pa enchyma issue and he ibe s occu s solely by di usion,
hus being e y slow [
38
]. Mo eo e , he ci cula ion h ough he essels is educed when
he culm is ha es ed and ma u ed. The e o e, yloses and limos p oduced on he neigh-
bo ing pa enchyma cells mo e owa ds he essels, blocking he conduc i e ca i y [
38
].
This phenomenon is clea ly obse able in he bundle o Figu e 8d.
Figu e 8.
SEM images o (
a
) longi udinal cu o AA, de ail o essel, (
b
) pa enchyma cells o AA,
(c) de ail o essels and cells o AA and (d) obs uc ed essels o DS.
Polyme s 2021,13, 2126 8 o 13
3.2. Mo phological Compa ison o Di e en Species
Figu e 10 shows pho og aphs o AA, DS, and PA bamboo culms bo h be o e and a e
wa e imme sion.
DS bamboo p esen s a e y ough su ace wi h high hickness, whe eas PA bamboo
shows a pe ec ly inished hinne su ace. The e a e also di e ences ega ding hei
we ing beha io a e wa e imme sion. Unlike he AA and DS samples, in he case o PA
bamboo, he wa e imp egna ion is clea ly isible in Figu e 10.
Figu e 9shows he OM images o he inne and ou e pa o he h ee di e en
species, oge he wi h hose o he ansi ion zones. Rega ding he inne pa s, i can
be obse ed ha he cen al pa o DS bamboo (Figu e 9b) p esen s exac ly he same
mo phology as he inne pa o he es o he species. I is no always hollow, e en hough
in he cen al pa almos e e y hing is pa enchyma. Small clus e s o ibe s wi h hei
essels a e ound, which allow he conduc ion o nu ien s o he cells o he cen al pa .
Howe e , on close obse a ion, i is no iceable ha ibe packages in DS bamboo p esen
an e a ic o ien a ion. The p emise ha he smalles bundles will always be close o
he ou side o he bamboo culm is no ul illed in his case. I can be s a ed ha each
g ouping is acing a di e en side. On he con a y, as can be seen in Figu e 9a,c, bo h AA
and PA main ain he a o emen ioned s uc u e, ollowing he pa h discussed h oughou
he manusc ip .
Figu e 9.
OM images o he inne pa o (
a
) AA, (
b
) DS and (
c
) PA species, oge he wi h hose
co esponding o he ansi ion zones o (
d
) AA, (
e
) DS and (
) PA species and he co esponding
images o he ou e pa s o (g) AA, (h) DS and (i) PA.
Analyzing he su ace a ea a io occupied by ibe s and pa enchyma, di e ences we e
ound be ween he h ee species. The a ea o be analyzed was he ou e pa , since i is he
mos in e es ing one in e ms o mechanical p ope ies. As could be obse ed in Figu e 11,
he p opo ion changes as i goes deepe in o he culm. The main di e ence was ound in
he epide mis, which is de ined in he i s 50
µ
m o PA and AA species, while o DS, i
ex ends beyond 200 µm.
Polyme s 2021,13, 2126 9 o 13
Figu e 10.
Pic u es o AA, DS and PA bamboo culms be o e ((
a
), (
b
), (
c
), espec i ely) and a e ((
d
),
(e), ( ), espec i ely) wa e imme sion.
Figu e 11.
Fibe pe cen age in he ans e sal sec ion o he culm o AA, PA, and DS bamboo species.
The ex e nal zone.
Rega ding he inne pa s, wo o he cha ac e is ics can be ound o DS bamboo ha
could di ec ly a ec he mechanical p ope ies. The i s one is he dis ance be ween he
ibe shea hs. As AA p esen s lowe pa enchyma cells densi y, he ibe s a e p esen . On he
o he hand, in he case o bo h he AA and DS species, he ibe shea hs appea ed o be
almos black, while o PA, hey we e clea e due o highe ligh e lec ion, indica ing lowe
ibe densi y. Fu he mo e, in he case o PA, he ibe shea hs a e much smalle han in he
DS and AA species, undoub edly being he weakes inne pa among he h ee species.
The so-called ansi ion zone be ween inne and ou e zones co esponds o a egion
o 5 mm close o he skin in he case o DS (Figu e 9e), and o he in e media e zone
be ween he ou e and inne egions o he es o he species. This pa o DS, compa ed
o ha o AA (Figu e 9d), shows ha he dis ance be ween ibe g oups is somewha highe .
In addi ion, mo e me axylem duc s a e obse ed bu no as much as in PA (Figu e 9 ).
Di e ences in he me axylem duc s o AA and DS species can be obse ed in Figu e 9g,h,
espec i ely. In he case o DS, hese duc s a e p esen no only in all he ex e nal pa s
bu also bo de ing he epide mis. This ac could allow o a be e esin imp egna ion
in he ex e nal pa , which could lead o a signi ican imp o emen o he mechanical
